Disc & Drum GMC Cab & Chassis V3500

REAR WHEEL ANTI-LOCK BRAKE SYSTEM

General Motors light duty trucks use a Rear Wheel Anti-Lock (RWAL) system to prevent wheel lock-up during heavy braking. This is done by regulating fluid pressure to rear wheel cylinders. Pressure regulating is adjusted by a control valve, located under the master cylinder. Control valve is controlled by an Electronic Control Unit (ECU), located next to master cylinder.

The ECU receives signals from a speed sensor, located in the transmission on 2WD models or in transfer case on 4WD models, and the stoplight switch. Speed sensor signal is sent through a digital ratio adapter which is part of the instrument cluster. If axle ratio or tire size is changed, recalibration of the digital ratio adapter must be performed. The system is disabled when vehicle is in 4WD.

On models equipped with automatic transmission, an in-line resistor, between module and stoplight switch, prevents battery voltage from energizing the transmission converter clutch solenoid. The RWAL system is connected to the existing brake warning light on the instrument panel. When ignition is turned on, warning light should come on for approximately 2 seconds to indicate system is operating.

The anti-lock brake system is covered under a separate article. See ANTI-LOCK BRAKE SYSTEM article in the BRAKES Section.

Delco-Moraine Single Diaphragm

A combined vacuum-hydraulic unit which uses a combination of intake manifold vacuum and atmospheric pressure to provide power assist. Reserve vacuum supply and vacuum check valve allow several brake applications, with vacuum assist, after engine has stopped.

Unit is composed of 2 main sections. The vacuum power cylinder and the dual master cylinder. Vacuum power cylinder contains power piston assembly, which houses control valve, reaction mechanism, and power piston return spring.

Delco-Moraine Tandem Diaphragm

Unit is mounted on firewall and connected directly to brake pedal. A combination of vacuum and atmospheric pressure is used to provide power assist.

Power cylinder houses power piston assembly, which contains primary and secondary diaphragms, pistons, floating control valve, reaction piston, and disc.

Bendix Hydro-Boost

System utilizes power steering pump fluid pressure to operate booster. The assembly contains an open-center spool valve which controls pump pressure during braking. Also a lever mechanism is used to control the position of the valve and a boost piston to operate master cylinder.

The unit also has a reserve system which stores sufficient fluid under pressure to provide at least 2 braking applications. Brakes can be applied manually if reserve system is depleted.

Delco Floating Caliper

Note. Delco floating caliper disc brakes are used on all gasoline engine models except those equipped with Bendix Hydro-Boost power brake units and/or 4-wheel disc brakes. All other models use Bendix sliding caliper disc brakes.

Delco floating caliper disc brake assembly uses a single piston caliper. The caliper is mounted to an anchor plate which is bolted to the steering knuckle. The caliper assembly floats through 4 rubber bushings on 2 steel guide pins or 2 mounting bolt and sleeve assemblies. Inboard brake pads have spring retainers which fit into caliper piston. Outboard pads either have tabs which are clinched to caliper or spring retainers which hold pad to caliper housing.

The pins or bolts are threaded into caliper anchor plate. When brakes are applied, hydraulic pressure is passed to caliper piston. This force pushes inner brake pad against inner rotor braking surface.

Pressure then moves caliper inward on guide pins or sleeves, thus forcing outer disc pad against outer rotor braking surface. When brakes are released, pressure is removed from cylinder. Rotor runout moves piston back off of rotor to maintain sufficient rotor-to-pad clearance.

Bendix Sliding Caliper

Note. Bendix sliding caliper disc brakes are used on all models equipped with Bendix Hydro-Boost power units, 4-wheel disc brakes, and/or diesel engines. All other models use Delco floating caliper disc brakes.

Bendix sliding caliper disc brakes use a single piston caliper. Front calipers are attached to a mount integral with the steering knuckle. Rear calipers are mounted to an adapter bolted to the drive axle.

When brakes are applied, hydraulic pressure is passed to caliper piston. This force is transmitted to inner brake pad against inner rotor braking surface. Pressure then moves caliper inward, forcing outer disc pads against outer braking surface.

When brake pedal is released, pressure is removed from caliper cylinder and rotor runout moves piston back into caliper cylinder to maintain sufficient rotor-to-pad clearance.

DRUM BRAKE - CONVENTIONAL DESIGN

Delco single anchor, duo-servo type brake assemblies are used on the rear of all models except light duty "C" series. The assemblies consist of a support plate, 2 brake shoes, return springs, automatic adjuster components and a duo-servo wheel cylinder.

Automatic adjusters consist of a connecting link, override lever, override spring, return spring, actuating lever and an adjusting screw. Normal adjustment is accomplished through movement of actuating lever and secondary shoe during application of brakes when vehicle is operated in reverse.

DRUM BRAKE - LEADING/TRAILING DESIGN

In the leading/trailing design drum brake system used on light duty "C" series, the return springs hold both shoes against the wheel cylinder at the top and against the fixed anchor at the bottom. When the brakes are applied, the wheel cylinder moves both shoes out to contact the drum. The forward shoe wraps itself into the drum and self-energizes during forward application. With application in reverse, the rear shoe wraps itself into the drum providing self-energization.

HEIGHT SENSING PROPORTIONING VALVE

General Motors 30 series pickups use a height sensing proportioning valve that responds to changes in vehicle height. This valve automatically provides optimum front-to-rear brake balance, regardless of vehicle load.

The valve controls pressure to rear brakes by sensing vehicle load conditions through relative movement between rear axle and body. As vehicle load increases (resulting in decreased vehicle height), higher brake line pressure to rear brakes is allowed.

PRESSURE DIFFERENTIAL BRAKE WARNING SWITCH

This switch is used to warn vehicle operator that one of the hydraulic systems has failed. When hydraulic pressure is equal in both front and rear systems, switch piston remains centered and does not contact terminal in switch

If brake system fails, hydraulic pressure moves piston toward failed side. Shoulder of piston then contacts switch terminal to provide for brake warning light.

PROPORTIONING VALVE

Valve operates by restricting, at a given ratio, hydraulic pressure to rear brakes when system hydraulic pressure reaches a certain point. This improves front-to-rear brake balance at high speed braking, when a percentage of rear weight is transferred to front wheels.

Valve reduces rear brake pressure, and delays rear wheel skid. On light brake application, valve allows full hydraulic pressure to rear brakes.

METERING VALVE

This valve holds off pressure to front disc brakes to allow rear drum brake shoes to overcome return spring pressure and make contact with rear drums. This prevents locking front brakes on slippery or icy surfaces under light braking conditions. Valve has no effect on front brake pressure during hard braking conditions.

Bendix/Delco-Moraine Dual Piston

Bendix and Delco-Moraine cast iron tandem dual piston master cylinders are single casting type with front and rear pistons and a separate reservoir and outlet for each piston.

Primary piston is operated by push rod connected to brake pedal. Secondary piston is operated by primary piston. In a combination disc and drum system, reservoir which feeds disc brakes is larger to compensate for larger displacement of disc caliper cylinder.

Bendix Mini-Master Cylinder

Functions of the Bendix Mini-Master cylinder are basically the same as a conventional master cylinder although components differ.

When cylinder is in released position, primary and secondary actuators are in contact with compensating valve stems which project into cylinder bore.

This keeps valves off their seat and opens communication between cylinder bore and reservoir. The initial forward movement of piston permits compensating valves to seat. This closes communication between pressure chambers in cylinder bore and reservoir. As piston travels further, pressure build up is transmitted to calipers and wheel cylinders.

Delco Quick Take-Up

The Delco Quick Take-Up master cylinder is a 2 piece unit with cast master cylinder body and plastic fluid reservoir. It is designed for use with systems utilizing low drag calipers.

This master cylinder includes a quick take-up valve. This valve delivers a large volume of fluid, at low pressure, upon initial application of brakes. The fluid quickly displaces retracted calipers, placing brake linings in contact with brake rotors and drums.

Released Position (No Braking)

With pedal released, spool valve return spring holds spool valve open. The spool valve allows fluid flow between power steering pump and power steering gear.

Fluid pressure is blocked from entering boost pressure chamber by lands on spool valve. Boost pressure chamber is vented through spool valve, to pump return port, and back to power steering pump.

Braking Position

As brake pedal is depressed, it moves pedal rod and spool valve. This closes fluid return to pump, and admits fluid into boost chamber from pressure port. Additional valve movement restricts flow between pump and steering gear.

As fluid pressure increases in boost chamber, it forces piston forward, actuating master cylinder piston and applying brakes. If fluid pressure is required for steering while braking, pump pressure will rise and spool valve will shift in an open direction allowing more fluid to flow to steering gear.

Reserve System

System consists of a charging valve, accumulator valve, and a spring loaded accumulator. Accumulator is integral with booster unit. System is open to pressure port of booster unit.

Charging valve has an orifice and ball check. Fluid from pump passes through orifice in valve, unseats ball check valve and enters accumulator. Ball check valve prevents reverse flow.

Accumulator valve is a poppet-type valve held closed by accumulator pressure. If no pump pressure is available, an actuator on spool valve sleeve opens accumulator valve. Fluid pressure can also enter accumulator from boost chamber through accumulator valve, when boost chamber pressure exceeds accumulator pressure.

A pressure relief valve vents accumulator to pump return port when pressure in accumulator exceeds approximately 1600 psi (112 kg/cm 2 ).

HYDRAULIC BRAKE BLEEDING

Note. On vehicles with ABS, wait 15 seconds between pedal strokes when bleeding brake system. On vehicles with Hydro-Boost, check for air bubbles in power steering fluid reservoir. If air bubbles are present, bleed Hydro-Boost system before bleeding brake system. See HYDRO-BOOST BLEEDING .

Hydraulic system bleeding is necessary any time air has been introduced into system. Bleed brakes at all 4 wheels if master cylinder lines have been disconnected or master cylinder has been run dry. Bleed brakes with pressure bleeding equipment or by manually pumping brake pedal while using bleeder tubes.

Hydro-Boost bleeding involves bleeding power steering system as well as brake system.

HYDRAULIC CONTROL VALVES

On disc brake equipped vehicles, metering section of hydraulic control valve must be deactivated before bleeding to permit fluid to flow to front brakes. This is especially important when pressure bleeding.

Use Combination Valve Depressor (J-23709 or J-25856) when applicable. (Scheme 3) If tool is not available, hold valve open by hand. DO NOT use "C" clamp or other non-yielding device to hold valve open.

Scheme 3

MANUAL BLEEDING

Note. When bleeding disc brakes, air may tend to cling to caliper walls. Lightly tap caliper, while bleeding, to aid in removal of air.

1. Fill master cylinder. Install bleeder hose to first bleeder valve to be serviced. See «BLEEDING SEQUENCE»(/gmc/cab-chassis-v3500/1987-1991/remont/mechanical-hydraulic/#disc-drum) table. Submerge other end of hose in clean glass jar partially filled with clean brake fluid.
2. Open bleeder valve 3/4-1 turn. Depress brake pedal slowly through full travel. Close bleeder valve and release pedal. Repeat procedure until flow of fluid shows no signs of air bubbles.

Scheme 4

PRESSURE TANK BLEEDING

1. Clean master cylinder cap and surrounding area. Remove cap. With pressure tank at least 1/2 full, connect to master cylinder with adapters. Attach bleeder hose to first bleeder valve to be serviced. See «BLEEDING SEQUENCE»(/gmc/cab-chassis-v3500/1987-1991/remont/mechanical-hydraulic/#disc-drum) table.
2. Place other end of hose in clean glass jar partially filled with clean brake fluid so end of hose is submerged in fluid. Open release valve on pressure bleeder. Follow equipment manufacturers pressure instructions unless noted below.
3. Unscrew bleeder valve 3/4-1 turn noting fluid flow. When fluid flowing from cylinder to jar is free of bubbles, close bleeder valve securely. Bleed remaining cylinders in correct sequence and in the same manner. Remove tool from control valve.

PRESSURE BLEEDER SETTINGS

BLEEDING SEQUENCE

Before bleeding system, exhaust all vacuum from power unit by depressing brake pedal several times. Bleed master cylinder if equipped with bleeder screws. Bleed slave cylinder on vehicles equipped with remote mount power assist units. Bleed wheel cylinders and calipers in sequence. See BLEEDING SEQUENCE table.

BLEEDING SEQUENCE

HYDRO-BOOST BLEEDING

Note. If power steering fluid has foamed, due to low fluid level, it will be necessary to park vehicle for approximately 1 hour (reservoir cap loose) so that foam can dissipate.

1. Fill reservoir with steering fluid and leave undisturbed for at least 2 minutes. Start engine and run momentarily. Add fluid if necessary. Repeat until fluid level remains constant after running engine.
2. Stop engine. Raise vehicle so front end is off the ground. Turn steering wheel right and left, lightly contacting stops. Add fluid if necessary.
3. Start engine and depress brake pedal several times while turning steering wheel from stop to stop. Turn engine off and depress brake pedal several times to deplete accumulator pressure. Add fluid if necessary.
4. If fluid is foamy, or has air in it, let vehicle stand several minutes, repeat procedures. The presence of air in the system will cause fluid level to rise with engine off. Continue to bleed system until all air is expelled.

DISC BRAKE

Pad wear is automatically compensated for by piston moving outward in cylinder bore. No disc pad adjustment in service is required.

Inspect condition of disc pads whenever wheels are removed. If any disc pad is worn to within 1/32" (.8 mm) of rivet heads, replace all disc pad sets on that axle.

DRUM BRAKE SHOE - CONVENTIONAL DESIGN

1. Knock out lanced area in brake drum with a punch. If drum is installed, it must be removed and all metal removed from brake area.
2. Turn adjusting screw, through hole, until brake shoes expand and brake drums can just be turned by hand. The drag should be equal at all wheels.
3. Back off adjusting screw 30 notches at each wheel. If drum still drags, back off an additional 1 or 2 notches. Install hole cover in drum.

Scheme 5

DRUM BRAKE SHOE - LEADING/TRAILING DESIGN

Drum brake shoes are adjusted with parking brake adjustment. See PARKING BRAKE - LEADING/TRAILING BRAKES under ADJUSTMENTS.

FRONT WHEEL BEARING - 2WD

Tighten bearing nut to 16 ft. lbs. (22 N.m) while spinning wheel forward. Back off nut until it is just loose. Hand-tighten nut, then loosen slightly (no more than 1/12 turn) until cotter pin can be inserted. End play should be .001-.005" (.03-.13 mm).

1. Raise vehicle. Allow rear axle to hang free (no load condition), with wheels on. Remove nut from valve shaft and remove lever assembly. (Scheme 6)
2. Rotate valve shaft to permit installation of adjustment gauge. Center hole of adjustment gauge must seat on "D" shape of valve shaft and gauge tang must seat in valve mounting hole. (Scheme 6)
3. Install lever on valve shaft by pushing plastic bushing and clip assembly over serrations on valve shaft using a "C" clamp or pliers. When properly installed, serrations on valve shaft fully engage plastic bushing. NOTE: DO NOT drive lever assembly on valve shaft by using nut as proper valve setting may be disturbed.
4. Install nut and tighten to 70-98 In. lbs. (8-11 N.m). Break tang on adjustment gauge to allow valve assembly to rotate freely. Lower vehicle and test brakes.

Scheme 6

MASTER CYLINDER PUSH ROD

Note. On some models, production push rod is not adjustable. If production rod is reused, gauging is to check proper assembly. If adjustable service push rod is used to replace production rod, use procedure to set to correct rod length.

Scheme 7

1. Place power unit in a vise with front housing up. Remove front seal to ensure all vacuum is released from unit. Place master cylinder rod, flat end first, in piston rod retainer. Press down on rod with 50 lbs. (23 kg) pressure to make sure rod is seated.
2. Place gauge (J-22647) over piston rod so it can be moved from left to right without contacting studs. The center section of gauge has 2 levels.
3. The piston rod should always contact the lower level and never contact the highest level. If the push rod does not contact gauge correctly, an adjustable push rod must be obtained.
4. Adjust locking screw on rod to obtain correct clearance with gauge. Apply silicone lubricant on the inside diameter of front housing seal and place seal in position in housing depression.

Rear Wheel Type (Foot Pedal Actuated)

1. With service brakes correctly adjusted, raise vehicle until both rear wheels are off ground. Loosen equalizer adjusting nut. Apply parking brake 4 notches from fully released position.
2. Tighten adjusting nut until a slight drag is felt when wheels are rotated forward. Tighten lock nut. Release parking brake and wheels should rotate forward freely. Lower vehicle.

Rear Wheel Type (Orscheln Lever Actuated)

1. With service brakes in proper adjustment, turn adjusting knob on lever counterclockwise to stop. Apply parking brake and raise vehicle until both rear wheels are off ground.
2. Loosen intermediate cable equalizer lock nut and adjust front nut until slight drag is felt when rear wheels are rotated forward. Tighten lock nut. Readjust lever adjusting knob to obtain definite snap-over-center feel. Release parking brake and check that no drag is present when wheels are rotated.

Transmission Mounted (Internal Shoe Type)

1. With at least 1 rear wheel raised off ground, block wheels and release parking brake. Remove cotter pin and clevis pin connecting pull rod and relay lever.
2. Rotate drum to bring one access hole into line with adjuster screw at bottom of brake shoes (manual transmission) or top of shoes (automatic transmission). Knock out plug in drum for access hole, if necessary.
3. Rotate adjusting screws with a screwdriver to expand shoes until tight against drum. Drum should not be able to be rotated by hand. Back off adjuster screw 10 notches. Place parking brake lever in full released position.
4. Pull on brake cable enough to take up slack in brake linkage. Adjust pull rod clevis to line up with hole in relay lever. Insert clevis pin and roller pin. Tighten clevis lock nut. Install a new plug in access hole in drum and lower vehicle.

PARKING BRAKE - LEADING/TRAILING BRAKES

1. Raise and support rear of vehicle. Remove rear wheels. Remove brake drums. Rotate parking brake adjusting screw until clearance between brake drum and shoes is .010-.020" (.25-.51 mm). Use brake drum diameter gauge to determine clearance.
2. Ensure stop on parking brake lever is in contact with edge of brake shoe web. If parking brake cable is holding stops off of shoe web, loosen cable adjusting nut. Tighten cable adjusting nut until lever stop begins to move off of shoe web.
3. Loosen cable adjusting nut until lever stop moves back toward lever stop and barely contacts the stop. Clearance should be no more than .020" (.51 mm) between lever stop and shoe web.
4. Install brake drums and wheels. Apply and release service brake pedal 30-35 times with normal pedal force, pausing about one second between pedal applications. Apply parking brake pedal 6 notches from fully released position.
5. Rear wheels should not be able to be rotated. Release parking brake and ensure wheels rotate freely. Lower vehicle.

Brake Pedal

1. Make adjustment in linkage until pedal travel is correct. Pedal travel is the distance pedal moves toward floor from a fully released position.
2. Pump pedal a minimum of 3 times with engine off before making measurement. Pedal travel should be 6" on all 4-wheel disc brake models, and 3 1/2" on all other models.

HYDRO-BOOST TESTING

Note. Hydro-Boost cannot cause noisy brakes, fading brake pedal, or pulling brakes. If one of these conditions exists, other components of brake system are at fault.

Preliminary Checks

Note. Make the following checks, and repairs if necessary, before performing any test on the Hydro-Boost system.

1. Check fluid levels in master cylinder and power steering pump. Check power steering pump drive belt. Check power steering hoses for leaks or kinks.
2. Check for air in brake fluid or power steering fluid. Check engine idle speed. Check steering pump for proper pressure.

Note. If problem cannot be found in preliminary steps or tests, check areas of brake system that might cause condition. See TROUBLE SHOOTING .

Hydro-Boost Functional Test

1. Make all preliminary checks. Place transmission in Neutral and stop engine. Apply brake several times to deplete accumulator reserve.
2. Hold brake depressed with medium pressure. Start engine. Brake pedal should fall slightly, then push back against foot. If no action is felt, booster system is not operating properly.

Accumulator Leakdown Test

1. Start engine, and charge accumulator by either applying brake with heavy pedal force or turning steering wheel lock-to-lock.
2. Turn off engine and wait 1 hour. There should be 1 power-assisted brake application with engine off.
3. If reserve system will not retain a charge for 1 hour, but functions normally immediately following charging; or if accumulator can be heard charging and discharging but will not hold a charge, accumulator valves are at fault. Power piston/accumulator must be replaced.

Note. If Hydro-Boost is not functioning, ensure power steering system is operating before replacing Hydro-Boost unit.

Scheme 8

HYDRO-BOOST TROUBLE SHOOTING

Note. Use the following diagnostic charts to diagnose the Hydro- Boost system.

Scheme 9

Scheme 10

Scheme 11

CLEANING & INSPECTION

Note. When servicing brake parts, do not create dust by grinding or sanding brake linings or by using compressed air. Use water dampened shop towel to remove dirt and dust from brake parts during disassembly.

DISC PAD INSPECTION

Pad wear is automatically compensated for by piston moving outward in cylinder bore. No disc pad adjustment is required. Inspect condition of disc pads whenever wheels are removed. If any pad is worn to within 1/32" (.8 mm) of rivet heads, replace all pad sets on axle.

DRUM BRAKE CLEANING

Clean all parts except the brake lining and the brake drums with brake cleaning solvent. To remove brake fluid contamination, clean all parts except the brake lining with denatured alcohol. Contaminated brake lining must be replaced.

DRUM BRAKE INSPECTION

1. Pull back the wheel cylinder dust boots and check for evidence of leakage. If evidence of leakage is noted, the cylinder should be disassembled, inspected and overhauled.
2. Polish the brake support plate ledges with fine emery cloth and inspect them for grooves that could restrict shoe movement. If grooves exist after polishing, the support plate must be replaced. Inspect lining wear pattern. If wear across the width of the lining is uneven, the drums should be checked for distortion, the shoes for correct positioning, and the support plate for distortion.
3. Inspect all springs for evidence of overheating and fractures. Self-adjusting cables should be inspected for kinks, fraying, or elongation of the eyelet. Inspect adjuster screws for freedom of rotation, and adjuster lever for wear and distortion.
4. Replace defective brake parts.

BRAKE BOOSTER - EXCEPT HYDRO-BOOST

Note. Power brake unit can be removed without removing master cylinder or disconnecting brake lines.

Removal

1. Disconnect vacuum line from check valve or power unit. Remove nuts securing master cylinder to power unit.
2. Pull master cylinder forward away from unit. Disconnect brake pedal from push rod. Remove power unit-to-firewall bolts and remove unit.

Installation

To install, reverse removal procedures. If equipped with adjustable push rod, adjust before installation. See MASTER CYLINDER PUSH ROD under ADJUSTMENTS.

1. Depress and release brake pedal several times to ensure all pressure is discharged from accumulator. Disconnect hoses from booster.
2. Clean all dirt from hydraulic line connections at booster and master cylinder. Remove nuts that secure master cylinder to booster and support bracket. Support master cylinder, and cover exposed end with clean cloth. NOTE: In most cases, it is not necessary to disconnect master cylinder brake lines to remove booster unit.
3. Remove booster pedal push rod cotter pin and disconnect push rod from brake pedal (Blazer and Pickups) or booster bracket pivot lever (Vans).
4. On Blazer and Pickup models, remove booster support bracket. On Vans, remove support braces. Remove booster bracket-to-firewall or support bracket nuts and remove booster assembly.

To install, reverse removal procedures. Lubricate pedal rod and linkage pivot bolts, pins, sleeves and bushings with lubricant (Delco Brake Lube). Bleed booster/power steering hydraulic system. Check brake pedal and stop lamp switch adjustment.

Note. Bleeding Hydro-Boost system is a separate procedure from bleeding the hydraulic systems. See HYDRO-BOOST BLEEDING .

DISC CALIPERS & PADS - DELCO FLOATING CALIPER

Note. There are two types of floating calipers used on truck models. Type 1 has spring steel shoe retainer spring attached to outboard shoe. Type 2 has no retainer spring and the outboard pad has ears that are clinched to caliper.

Type 1 Removal

1. Remove 2/3 of brake fluid from master cylinder reservoir. Raise and support vehicle. Remove wheel assembly. Place large adjustable pliers over inboard shoe tab and the rear caliper housing. Squeeze pliers to bottom piston in bore.
2. Remove caliper mounting bolts and sleeves. If caliper is to be removed for service, remove brake hose inlet fitting and plug to prevent contamination. Remove caliper from vehicle or support with wire to prevent damage to brake hose.
3. Remove outboard shoe by disengaging spring buttons with screwdriver. Remove inboard shoe. Inspect bolt boots for nicks, cuts or corrosion. Replace if damaged. Inspect mounting bolts and sleeves for corrosion. If corrosion is found, replace bolts, sleeves, bushings and seals. DO NOT attempt to polish away corrosion.

Scheme 12

1. Lubricate mounting bolt bushings and bolt seals with silicone grease. Install bushings and seals in mounting bolt holes. Install bolt boots in caliper housing. Fill cavities between mounting bolt bushings with silicone grease.
2. Install inboard pad and snap retainer spring into caliper piston. Ensure that shoe is flush against piston. Install outboard pad with wear at leading edge of shoe with forward wheel rotation. Ensure that shoe is flat against caliper housing and shoe retainer spring buttons are seated in notches.
3. Install caliper over rotor and install mounting bolts and sleeves. Torque mounting bolts to 28 ft. lbs. (38 N.m). Ensure that bolt boots stay seated after tightening bolts.
4. Measure clearance between caliper and the bracket stops. If necessary, remove caliper and file ends of bracket stops to obtain proper clearance. (Scheme 12)
5. Install brake hose (if removed) with new gaskets and tighten inlet fitting to 32 ft. lbs. (43 N.m). Fill master cylinder to proper level and bleed brake system if necessary.

Type 2 Removal

1. Remove 2/3 of brake fluid from front reservoir in master cylinder. Raise vehicle and support with safety stands. Remove wheel assembly. Place a large "C" clamp on caliper so that solid side of clamp rests against metal part of outer disc pad.
2. Tighten "C" clamp until caliper moves away from vehicle far enough to push piston to bottom of bore. Remove "C" clamp. DO NOT disconnect brake line to caliper. Remove 2 mounting bolts which retain caliper to support bracket.
3. Lift caliper off rotor and remove inner disc pad. Pry out outer disc pad. Place caliper on front suspension arm so that caliper weight is not supported by brake hose.
4. Remove shoe support spring from cavity in piston. Remove sleeves from inner ear in caliper. Remove rubber bushings from grooves in each of 4 caliper ears.

1. Install new rubber bushings in 4 caliper ears. Install sleeves in bushings with installer tool (J-22835). Position sleeves so that end toward disc pad is flush with machined surface of ear.
2. Install shoe support spring on inner disc pad. Place single tang end of spring over notch in center edge of pad. Now press 2 tangs at spring end of inner disc pad over bottom edge of pad.
3. Place inner disc pad in caliper (with spring attached) so that the ear end of disc pad is down and the bottom end is up. Install at an angle so that the spring rests on the inside diameter of piston.
4. Press down on both ends of disc pad until pad is in a flat position, resting on piston. Be sure to install inner brake pads on the correct side. Wear sensor will be toward the rear of the caliper when correctly installed.
5. Place outer disc pad in caliper with ears of pad over caliper ears. Tab at bottom of pad should be engaged in caliper cut-out. Note left and right disc pads. Place caliper over rotor, line up caliper ears with holes in the mounting bracket.
6. With caliper in place, make sure brake hose is not twisted. Start bolts through sleeves in inner caliper ears and mounting bracket. Make sure that bolts pass under retaining ears in inner disc pad.
7. Push bolts through holes in outer disc pads and caliper ears. Thread bolts into mounting bracket and tighten to 35 ft. lbs. (48 N.m). Fill master cylinder with new brake fluid.
8. Pump brake pedal several times to seat disc pads against rotor. Clinch upper ears of outer disc pad with channel lock pliers, placing 1 jaw on top of upper ear and other jaw on bottom of disc pad, in notch.
9. After clinching, ears should be flat against caliper housing with no radial clearance. If clearance exists, repeat procedure.

1. To prevent master cylinder overflow when caliper is depressed, remove 2/3 of the brake fluid from master cylinder. Raise vehicle and support with safety stands.
2. Remove wheel assembly. Place a large "C" clamp on caliper and tighten clamp on bottom piston in cylinder bore. Remove clamp. Remove key retaining screw.
3. Drive out caliper support key and spring with brass rod and light hammer. Remove caliper by pushing down against mount and rotating up and away from mount.
4. Support caliper with wire. DO NOT let caliper hang with weight on brake hose. Remove inner disc pad and shoe clip from caliper.
5. Remove outer disc pad from caliper. It may be necessary to tap pad to loosen it in caliper housing.

1. Lubricate caliper and mount sliding surfaces with silicone lubricant. Install new anti-rattle clip in mount. Place lower end of inner pad into mount and against anti-rattle clip.
2. Slide upper end of pad into place. Be sure clip is still in correct position. With caliper piston fully bottomed in cylinder bore. Position outer pad on caliper and press tabs into place.
3. If pad cannot be properly positioned by hand, use a large "C" clamp, taking care not to mar lining. With disc pads installed, lift caliper and rest bottom edge of outer pad on outer edge of rotor.
4. Check that there is no clearance between bottom tab of outer pad and caliper abutment. Outer pad should be tight in caliper housing. Position caliper on mounting surface.
5. Place spring over support key and tap into place until key retaining screw can be installed. Tighten screw. Fill master cylinder with new brake fluid. Reinstall wheel assembly and lower vehicle.

Scheme 13

Removal & Installation

Brake caliper removal and installation procedures are same as for disc brake pads, except that it will be necessary to disconnect brake hose.

1. Raise vehicle and support with safety stands. Remove brake caliper ( DO NOT disconnect brake line).
2. Remove grease cover from end of hub. Remove cotter pin nut, washer, and outer bearing. Remove rotor and hub assembly.

Install rotor and hub assembly on spindle. Install outer bearing, washer, and nut. Adjust wheel bearings. See Wheel Bearing Adjustment in appropriate SUSPENSION article listed below.

1988

1. «SUSPENSION - FRONT (2WD)»(ref-46126) - Astro/Safari, S10/S15, S10 Blazer/S15 Jimmy
2. «SUSPENSION - FRONT (2WD)»(ref-46127) - C1500, C2500, C3500 Pickup
3. «SUSPENSION - FRONT (2WD)»(ref-46129) - R20/R2500 & R30/R3500 Pickup, R10/R1500 & R20/R2500 Suburban
4. «SUSPENSION - FRONT (2WD)»(ref-46130) - G10/G1500, G20/G2500, G30/G3500, P20/P25, P30/P35 Van

1989

1. «SUSPENSION - FRONT (2WD)»(ref-46132) - Astro/Safari, S10/S15, S10 Blazer/S15 Jimmy
2. «SUSPENSION - FRONT (2WD)»(/gmc/cab-chassis-v3500/1987-1991/remont/suspension-front/#suspension-front-r-series-2wd) - R2500/R3500 Pickup, R1500/R2500 Suburban
3. «SUSPENSION - FRONT (2WD)»(/gmc/cab-chassis-v3500/1987-1991/remont/suspension-front/#suspension-front-c-series-2wd) - C1500, C2500, C3500 Pickkup
4. «SUSPENSION - FRONT (2WD)»(ref-46136) - G10/G1500, G20/G2500, G30/G3500, P20/P25, P30/P35 Van

Remove brake caliper ( DO NOT disconnect brake hose). See DISC CALIPERS & PADS - DELCO FLOATING CALIPER or DISC CALIPERS & PADS - BENDIX SLIDING CALIPER under REMOVAL & INSTALLATION. Remove rotor. If rotor does not come off freely, remove axle nut, remove 4 hub bolts from rear of knuckle, pull hub from knuckles. Separate rotor from hub by backing out wheel studs with a dead-blow hammer. To install, reverse removal procedure.

1. Raise vehicle and support with safety stands. Remove wheel assemblies. On vehicles with automatic locking hubs, remove 5 screws, retaining hub cover to outer clutch housing.
2. Remove cover, seal, seal bridge, and bearing components. Use needle nose pliers to compress wire retaining ring. (Scheme 14) Pull remaining components from wheel.
3. On vehicles with manual locking hubs, remove Allen head screws. Remove outer locking hub locking assembly. Remove snap ring from end of axle shaft. Remove body assembly internal snap ring from hub. Remove body assembly.
4. On all vehicles, remove wheel bearing outer lock nut, retainer, and inner bearing adjustment nut using Wrench (J-6893) and Adapter (J-6893-01). Remove hub and disc assembly. Remove outer wheel bearing.
5. Remove oil seal and inner wheel bearing. Remove inner and outer wheel bearing cups (if necessary) using a brass drift and hammer. Clean and inspect all parts, as required.

Automatic Locking Hub Assembly Adjustment nut pin must pass through hole in drag sleeve washer. Scheme 14

1. Install bearing cups, if removed. Lubricate wheel bearings with high temperature wheel bearing grease. Install inner bearing and oil seal. Install hub and disc assembly. Install outer wheel bearing.
2. Tighten adjustment nut to 50 ft. lbs. (68 N.m) while rotating hub. Back off adjustment nut. On vehicles with automatic locking hubs, retighten nut to 35 ft. lbs. (47 N.m) while rotating hub. Back off adjustment nut 3/8 turn (maximum).
3. On vehicles with manual locking hubs, retighten nut to 50 ft. lbs. (68 N.m) while rotating hub. Back off adjustment nut just enough to free bearing. On all vehicles, install retainer. Tang on inside diameter of washer should fit into slot of spindle.
4. Move adjustment nut (if necessary) to align a hole in drag sleeve washer with pin on lock nut. Tighten lock nut to 160 ft. lbs. (217 N.m). Wheel bearing end play should be .001-.010" (.025-.254 mm).
5. On vehicles with automatic locking hubs, install retaining ring in groove of unsplined end of outer clutch housing, with tangs pointing away from housing. Hold tangs of retainer together and assemble seal bridge retainer over tangs. NOTE: Seal bridge retainer holds retainer in a clamped condition in groove of outer clutch housing. On "K" 10/20 vehicles, assemble "O" ring in groove of outer clutch housing and over seal bridge. This "O" ring may be left on, but is not required.
6. Lubricate bearing and install bearing over inner race. Steel balls should be visible when bearing is properly installed. Install bearing retainer clip into hole of outer race.
7. Install bearing and retainer assembly on end of hub sleeve. Install seal ring over outer clutch housing. Install bearing race spring into bore of cover. Install cover and spring assembly.
8. Align hole in cover with holes in outer clutch housing and install screws. Ensure that hub sleeve and attached parts turn freely after unit as been installed. Tighten cover screws to 45 INCH lbs. (5 N.m).
9. On manual locking hubs, install body assembly. Install body assembly internal snap ring into hub. Install snap ring on axle shaft. Install outer hub assembly. Install Allen head screws. On all vehicles, reverse removal procedure to complete installation.

1. Raise vehicle and support with safety stands. Remove wheel assembly and brake drum. It may be necessary to back off brake shoe adjustment before removing drum. Unlock primary and secondary shoe springs. Remove shoe hold down springs. NOTE: On some vehicles, it may be necessary to remove axle shafts to remove hub and drum.
2. Lift up on actuator, unhook actuating link from anchor pin and remove link. Spread shoes enough to clear wheel cylinder links. Remove parking brake strut and spring. Disconnect cable from lever. Remove brake shoes.

1. Lubricate fulcrum end of parking brake lever with brake lubricant. Attach lever to secondary shoe. Make sure lever moves free. Connect brake shoes together with adjuster spring.
2. Place adjuster screw in position. Make sure spring does not contact starwheel portion of adjusting screw. Right hand thread adjusting screw should be on left side.
3. Make sure starwheel lines up with hole in backing plate. Apply a thin coating of brake lubricant to contact surface on backing plate. Position brake shoes on backing plate.
4. Primary shoe (short lining) is to front. Connect cable to parking brake lever. Install strut between shoes. Install actuator, return spring and actuator link. Install shoe hold down springs.
5. Install both primary and secondary shoe springs. Measure inside diameter of brake drum with measuring gauge (J-21177). Expand brake shoes to dimension obtained on outside caliper portion of tool.
6. Install brake drum and wheel assembly. Bleed system if any portion of hydraulic system was opened. Check fluid level in master cylinder and add as necessary.

MASTER CYLINDER

1. Disconnect front and rear hydraulic brake lines at master cylinder, and cover ends to prevent entry of foreign matter.
2. On vehicles without power assist units, disconnect brake pedal push rod at brake pedal. Remove master cylinder retaining bolts, and remove cylinder assembly from vehicle.

1. Position master cylinder on vehicle and install cylinder retaining bolts. Connect front and rear hydraulic brake lines to cylinder.
2. Connect brake pedal push rod, if removed. Fill reservoir with clean brake fluid, and bleed hydraulic system. See «HYDRAULIC BRAKE BLEEDING»(/gmc/cab-chassis-v3500/1987-1991/remont/mechanical-hydraulic/#disc-drum__hydraulic-brake-bleeding) .

1. Raise vehicle and support with safety stands. Remove wheel assembly and brake drum. Loosen differential cover plate and drain lubricant from axle. Remove cover plate.
2. On 8 1/2" and 9 1/2" ring gear axles, remove differential pinion shaft lock screw. Remove differential pinion shaft. Push flanged end of axle toward center of vehicle and remove "C" clip from end of shaft.
3. Remove axle shaft from housing, being careful not to damage oil seal. When removing axle shaft on 9 1/2" ring gear axle, make sure that thrust washer in differential case does not slide out.
4. On Eaton locking axle, rotate differential case until lock screw is just above center line of rear axle housing. Support pinion shaft so that it cannot fall into case, then remove lock bolt.
5. Partially withdraw pinion shaft. (Scheme 15) Rotate differential case upward until shaft touches housing. Reach into case with screwdriver and rotate "C" lock until its open end points directly upward. Axle cannot be pushed inward until "C" lock is properly positioned NOTE: DO NOT force or hammer axle shaft in an attempt to gain clearance.
6. When "C" lock is positioned to pass through end of thrust block, push axle shaft inward and remove "C" lock. Carefully remove axle shaft.
7. On 8 1/2" ring gear axle, insert Bearing Remover (J-23689) behind bearing. Tighten nut finger tight against washer. Attach Slide Hammer (J-2619-01) to remover, remove bearing and seal.
8. On Eaton and 9 1/2" ring gear axles, insert Wobble Plate (J-29712) into axle tube so that it grabs behind bearing. Center receiver on axle tube and tighten nut. Back off nut, remove bearing and seal.

1. Lubricate bearing and seal lips with wheel bearing grease. Install bearing using Bearing Installer (J-23690) for 8 1/2" ring gear axle; (J-29709) on Eaton and 9 1/2" ring gear axles. Install bearing until installer bottoms against tube.
2. Install oil seal using Oil Seal Installer (J-21128) for 8 1/2" ring gear axle; (J-29713) on Eaton and 9 1/2" ring gear axles. Install seal until it is flush with end of tube.
3. Carefully install axle shaft. Ensure that splines on shaft engage splines on side gear. On 8 1/2" and 9 1/2" ring gear axles, push flanged end of axle shaft toward center of axle and install "C" clip.
4. Pull axle shaft outward until "C" clips seats in side gear. Install pinion shaft, making sure that hole in shaft is lined up with lock screw hole. Install new lock screw and tighten to 25 ft. lbs. (34 N.m).
5. On Eaton locking ring gear axle, install "C" lock while keeping pinion shaft partially withdrawn. Place "C" lock in thrust block. (Scheme 15) Carefully withdraw axle shaft until "C" lock is clear of thrust block.
6. When both locks are installed, install pinion shaft. Align hole in shaft with lock screw hole. Install new lock screw and tighten to 25 ft. lbs. (34 N.m).
7. On all models, install cover plate using a new gasket. Fill axle with lubricant to a level even with bottom of filler hole. Reverse removal procedure to complete installation.

Scheme 15

1. Remove bolts that attach axle shaft flange to wheel hub. Strike flange with hammer to loosen shaft. Grip rib on end of flange with locking pliers and twist shaft to start shaft removal.
2. Remove axle shaft from tube. Straighten tang of retainer from slot or flat of lock nut. Using Socket (J-2222), remove lock nut from tube. Straighten tang of retainer from slot or flat of adjustment nut. Remove adjustment nut. Remove thrust washer and hub/drum assembly.
3. If necessary use a long drift and hammer, to remove inner bearing, race, and oil seal from hub. Remove outer bearing snap ring. Using Bearing Remover (J-24426) and handle, remove outer bearing and race from hub.

1. Pack wheel bearings. Place outer bearing into hub. Install race of outer bearing into hub using handle and Bearing Installer (J-8608). Drive race beyond snap ring groove.
2. Install snap ring. Press race of outer bearing against snap ring using bearing remover. Using Bearing Installer (J-24427), install inner bearing race. Install race until it seats against shoulder of hub bore. Install new oil seal.
3. Install hub/drum assembly on axle housing. Install thrust washer so that tang on inside diameter of washer is key way on axle housing. Install adjustment nut and tighten to 50 ft. lbs. (68 N.m) while rotating hub. Back off adjustment nut until loose.
4. If adjustment nut is aligned with keyway in spindle, insert square key into slot. If adjustment nut is not aligned, slightly back off nut and insert square key in slot. DO NOT back off nut more than one slot to align key. Reverse removal procedure to complete installation.

Remove wheel assembly, drum, and brake shoes. Remove cylinder connecting links and disconnect hydraulic brake line from cylinder. Remove brake cylinder retaining bolts and remove cylinder from support plate. To install, reverse removal procedures.

Remove negative battery cable. Disconnect electrical connector at switch and remove switch. Installation is reverse of removal. Adjust switch, see ADJUSTMENT .

Adjustment

Depress brake pedal. Pull lever at bottom of brake switch back to the stop. Pull brake pedal against stop.

Disassembly

1. Scribe marks on housings for reassembly reference and remove boot, front housing seal, vacuum check valve and grommet.
2. Attach power unit front housing to holding fixture base (J-22805-1) and clamp base in vise with power section up.
3. Place a spanner wrench (J-9504) on studs of rear housing. Press down and turn counterclockwise to unlock housings. NOTE: DO NOT put pressure on plastic power piston extension.
4. Remove power piston bearing, return spring and power piston group. Remove piston rod and reaction retainer. CAUTION: Use care not to damage power piston assembly when removing reaction disc. Reaction disc must be replaced.
5. Use awl, ice pick or similar tool to remove reaction disc. Remove reaction piston. Grasp assembly at outside edge of diaphragm support and diaphragm.
6. Hold pushrod down against a hard surface. Use a slight force or impact to dislodge diaphragm retainer.

Typical Delco-Moraine Single Diaphragm Power Brake Unit Do not disassemble power push rod assembly. Scheme 16

1. Clean all metal, plastic, and rubber parts in denatured alcohol. Blow out all passages, orifices, and valve holes with clean, dry air. Air dry all parts.
2. Slight rust on inside of housings can be polished with crocus or emery cloth. There should not be any nicks or cuts on rubber part. Replace any damaged part.

Reassembly

1. Lubricate inside diameter of diaphragm lip with silicon lubricant and fit in diaphragm support.
2. Install diaphragm and support over power piston and push rod assembly, support side first. Install new diaphragm retainer and seat using Seating Tool (J-28458) and a soft mallet.
3. Install reaction piston, new reaction disc, reaction retainer and piston rod.
4. Attach holding fixture to front housing and place in vise. Install power piston return spring with White end to front housing.
5. Insert power piston assembly pushrod end through rear housing and place on front housing and return spring.
6. Align scribe marks with spanner on studs of rear housing. Press down and turn clockwise to lock housings. NOTE: Assembly can be aided by connecting a vacuum source to booster.
7. Stake 2 housing tabs into sockets with screwdriver. Stake 2 tabs at 180° apart.
8. Lubricate inside and outside diameters of grommet and front housing seal and install seal, grommet, vacuum check valve and boot.

1. Remove push rod boot, silencer, front housing seal, grommet, and vacuum check valve. Scribe a mark on front and rear housing for reassembly reference. Attach front housing to holding fixture (J-22805-01).
2. Place spanner wrench (J-9504) over rear housing studs, press down, and turn counterclockwise to unlock housings. Carefully separate housings. Remove power piston group, power piston return spring, and power piston bearing.
3. Remove push rod, reaction retainer and power head silencer. Grasp assembly at outside edge of divider and diaphragms. Hold with push rod down against a hard surface.
4. Use a slight force or impact to dislodge diaphragm retainer. Remove primary diaphragm, primary support plate and secondary power piston bearing. Remove housing divider, secondary support plate and diaphragm and power piston assembly.

1. Clean all plastic, metal and rubber parts in denatured alcohol. Blow out all passages, orifices and valve holes. Air dry all parts.
2. Slight rust on housing may be cleaned with crocus or emery cloth. DO NOT reinstall any rubber parts with cuts, nicks or distortion. If in doubt, replace the part.

Scheme 17

Scheme 18

Note. Lubricate rubber, plastic, and metal friction parts with silicone lube before assembly.

Scheme 19

1. Place power piston on bench with push rod end up. Install assembly cone (J-28458) over push rod end of piston. Lubricate inside diameter of secondary diaphragm with silicone lubricant and fit in secondary support plate.
2. Install secondary diaphragm and support plate over power piston and push down until it bottoms. (Scheme 19) Lubricate inside diameter of secondary power piston bearing and install in housing divider with flat surface of bearing on the same side as 6 raised lugs on divider.
3. Hold divider so that formed over flange faces up. Press divider down over assembly cone and onto power piston to rest against secondary diaphragm. Lubricate inside diameter of primary diaphragm and install in primary support plate.
4. Remove assembly cone from power piston. Place primary support plate and diaphragm assembly over power piston and push down until it bottoms. Place diaphragm retainer over power piston and onto diaphragm.
5. Install assembly cone (J-28458) over power piston onto diaphragm retainer and strike with hammer until retainer is locked on neck of power piston. Remove assembly cone.
6. Install reaction retainer, piston rod, and power head silencer. Place primary power piston bearing in rear housing center hole. Lubricate with silicone lubricant on inner diameter.
7. Attach front housing to holding fixture and place fixture in vise. Install power piston assembly to rear housing. Install power piston return spring over reaction retainer and lower rear housing onto front housing.
8. Align scribe marks and press down on spanner wrench (J-9504), turning clockwise to lock housings. Stake 2 housing tabs into sockets at 2 locations 180° apart.
9. Lubricate inside and outside diameters of grommet and front housing seal. Install seal, grommet, vacuum check valve, silencer, and push rod boot.

BRAKE BOOSTER - BENDIX HYDRO-BOOST

Scheme 20

1. Secure unit in vise. DO NOT clamp accumulator. Place "C" clamp and Accumulator Cap Retainer (J-26889) over end of accumulator and install nut onto master cylinder mounting stud. (Scheme 20)
2. Depress accumulator with clamp. Insert punch into hole on housing. Release clamp and remove cap retainer.
3. Remove the following: accumulator, "O" ring, retainer, spool plug, "O" ring, spool return spring, spring and baffle retainer, output pushrod, baffle, and piston return spring.
4. Saw off eyelet of pedal rod. Remove the following: pedal rod boot, bracket nut, bracket and housing cover bolts.
5. Separate cover from housing. Remove the following: housing seal, piston assembly, spool valve and accumulator valve. (Scheme 21)

Scheme 21

Scheme 22

Use only power steering fluid to clean all parts. Lubricate all seals and metal friction parts with power steering fluid. If any of the accumulator valve components are damaged or lost, replace all valve components.

Scheme 23

Lubricate seals and metal friction points with power steering fluid. Install all components in reverse order.

HYDRO-BOOST TORQUE SPECIFICATIONS

Scheme 24

Scheme 25

1. Clean exterior of caliper with denatured alcohol and place on clean work surface. Remove brake hose, discarding copper gasket. Drain brake fluid from caliper.
2. Use clean shop towels to pad interior of caliper and apply compressed air at caliper inlet to remove piston. Use just enough pressure to ease piston out of bore. WARNING: DO NOT attempt to catch or protect piston with fingers while applying compressed air. Injury may result. Always use eye protection when performing this step. (Scheme 25): Using Compressed Air to Remove Caliper Piston Compressed air must be filtered and dry.
3. Use screwdriver to pry boot out of caliper housing. Pry piston seal from its groove in caliper bore with a piece of wood or plastic. DO NOT use metal tool of any type to remove piston seal. Remove bleeder valve from housing.

Scheme 26

Scheme 27

Inspection

1. Boot, seal, rubber bushings, and sleeves are to be replaced each time caliper is overhauled. Clean all other parts in denatured alcohol. Dry parts with dry compressed air. NOTE: Using lubricated shop air will leave a film of mineral oil on metal parts. This may damage rubber parts upon contact during reassembly.
2. Check mounting bolts and sleeves on type 1 caliper or guide pins on type 2 caliper for corrosion, breaks in plating or other damage. DO NOT attempt to clean pins, bolts or sleeves; replace them. Check outside diameter of piston for scoring, nicks, corrosion, and worn or damaged plating. If surface defects exist, piston must be replaced.
3. Piston bore should be checked for similar defects. Bore is not plated, therefore, it may be polished with crocus cloth. Thoroughly clean after polishing. Replace caliper housing if bore corrosion cannot easily be cleaned out.

1. Lubricate bore in caliper housing and new piston seal with clean brake fluid. Position seal in caliper bore groove.
2. Lubricate piston with clean brake fluid and assemble new boot into groove in piston with fold facing open end of piston.
3. Insert piston into caliper bore using care not to unseat seal. Force piston to bottom of bore. Position outer diameter of boot in caliper counterbore and drive in until fully seated.
4. Check boot installations to ensure retaining ring (molded into boot) is not bent, and that boot is installed completely below caliper face. Install brake hose, using new copper gasket.

Scheme 28

1. Wipe caliper clean around inlet port and remove plug. Drain fluid from caliper housing. Place caliper assembly on bench (piston side up).
2. Place several shop towels between piston and outer legs of caliper housing. Carefully apply low-pressure air at caliper inlet port until piston comes out of caliper housing. WARNING: DO NOT attempt to catch or protect piston with fingers while applying compressed air. Injury may result. Always use eye protection when performing this step.
3. If piston is seized, lightly tap around end of piston with soft-faced hammer. DO NOT attempt to catch piston by hand, since it may pop out of caliper with some force. (Scheme 28): Using Compressed Air to Remove Caliper Piston Place shop towels under caliper to catch piston.
4. Remove boot from piston and seal from cylinder bore. Clean caliper housing and piston with denatured alcohol. Check cylinder bore, seal groove, and boot groove for damage or excessive wear. Replace piston if pitted.

Exploded View of Bendix Sliding Caliper Assembly. Scheme 29

To assemble caliper, soak all parts in new brake fluid and reverse disassembly procedures. Use large "C" clamp to seat piston in cylinder bore.

1. Raise vehicle and support with safety stands. Remove wheel assembly and brake drum. It may be necessary to back off brake shoe adjustment before removing drum. Unlock primary and secondary shoe springs. Remove shoe hold down springs. NOTE: On some vehicles, it may be necessary to remove axle shafts to remove hub and drum.
2. Lift up on actuator, unhook actuating link from anchor pin and remove link. Spread shoes enough to clear wheel cylinder links. Remove parking brake strut and spring. Disconnect cable from lever. Remove brake shoes.

1. Lubricate fulcrum end of parking brake lever with brake lubricant. Attach lever to secondary shoe. Make sure lever moves free. Connect brake shoes together with adjuster spring.
2. Place adjuster screw in position. Make sure spring does not contact starwheel portion of adjusting screw. Right hand thread adjusting screw should be on left side.
3. Make sure starwheel lines up with hole in backing plate. Apply a thin coating of brake lubricant to contact surface on backing plate. Position brake shoes on backing plate.
4. Primary shoe (short lining) is to front. Connect cable to parking brake lever. Install strut between shoes. Install actuator, return spring and actuator link. Install shoe hold down springs.
5. Install both primary and secondary shoe springs. Measure inside diameter of brake drum with measuring gauge (J-21177). Expand brake shoes to dimension obtained on outside caliper portion of tool.
6. Install brake drum and wheel assembly. Bleed system if any portion of hydraulic system was opened. Check fluid level in master cylinder and add as necessary.

1. Clean outside of cylinder thoroughly and remove cover. Drain fluid, and turn cylinder over, pump piston to remove any remaining fluid.
2. On manual brake models, remove boot from cylinder to uncover push rod retainer. Pry up retainer tab to release retainer.
3. On all models, push piston down into cylinder bore. Remove secondary piston stop bolt from front fluid reservoir (if equipped). Remove snap ring from groove in cylinder bore.
4. Remove both piston assemblies. Remove any internal parts remaining in bore.
5. Enlarge holes in tube seats using a 13/16" drill. Place a large flat washer over outlets and thread a 1/4" x 20 x 3/4" screw into seat.
6. Remove seat, screw and washer. Thread a 6 x 32 x 5/8" self tapping screw into tube seat, and push upward with 2 screw-drivers to remove seat.

Removing Tube Seat from Master Cylinder. Scheme 30

Inspect cylinder bore for scoring or corrosion. Staining which has not pitted or roughened surface of cylinder can be removed with crocus cloth. If cylinder bore is scored, pitted or corroded, it should be replaced.

1. Install replacement tube seats by threading a spare brake line tube nut into hole. Turn nut in until tube seat bottoms. DO NOT cock tube seat in hole.
2. Remove nut and check for burrs which may have been loosened by nut. Install piston cups on secondary piston, with cup lips facing away from each other.
3. Install seal protector, piston seal, spring retainer and return spring on secondary piston. Install seal so lip faces interior of master cylinder when installed.
4. Lubricate cylinder bore with clean brake fluid and install secondary piston assembly. Lubricate primary piston seals and install primary piston assembly in bore.
5. Hold primary piston down in bore and install snap ring in groove in bore. Install secondary piston stop bolt (if equipped).
6. Install master cylinder cover and new diaphragm. On vehicles with manual brakes, assemble brake pedal push rod through retainer (if used), and push retainer over end of master cylinder. Install rubber boot over push rod.

Exploded View of Typical Delco-Moraine Master Cylinder Bendix master cylinders are similar. Scheme 31

1. Remove reservoir cover and diaphragm. Drain all brake fluid. Remove 4 reservoir bolts and separate reservoir and master cylinder body. Remove small "O" ring and both compensating valve seals from bottom of reservoir.
2. DO NOT remove 2 filters from bottom of reservoir unless they are damaged. Push in primary piston and remove compensating valve poppets and springs from ports in master cylinder body.
3. Remove snap ring from master cylinder bore using a small screwdriver. Release primary and secondary pistons and remove from bore.
4. It may be necessary to plug front outlet port and apply low air pressure to front compensating valve port to remove secondary piston assembly.

Clean all reusable components in clean brake fluid. Make sure filters in bottom of reservoir are clean. If filters do not clean thoroughly, they must be replaced. After cleaning, inspect all components for wear or damage and replace as necessary.

1. Lubricate primary and secondary pistons, and cylinder bore with clean brake fluid. Position secondary spring (short spring) in open end of secondary piston actuator.
2. Position return spring (long spring) on projection at rear of secondary piston. Place secondary piston, actuator end first, in master cylinder bore and press assembly into bottom of bore. Insert primary piston, actuator end first into bore.
3. Using a smooth round end tool with snap ring placed over it, depress piston in bore. Install snap ring in groove. Place compensating valve seals and small "O" ring seal in recesses in bottom of reservoir. Make sure seals are fully seated.
4. Depress pistons and place compensating valve springs and poppets in valve ports. With piston still depressed, place reservoir in position. Install bolts and tighten to 12-15 ft. lbs. (16-20 N.m).

1. Remove reservoir cover and diaphragm. Discard remaining brake fluid in reservoir. Push in on primary piston and remove snap ring.
2. Apply compressed air at forward brake line hole while plugging rear hole. Pistons will be forced out at open end of master cylinder.
3. Remove spring retainer and seals from secondary piston. Discard seals. Clamp mounting ear of master cylinder in vise and pry off reservoir.
4. DO NOT attempt to remove take-up valve from master cylinder. It is not a serviceable component. Remove reservoir grommets and discard.

Exploded View of Quick Take-Up Master Cylinder. Scheme 32

Inspect cylinder bore for scoring or corrosion. If signs of corrosion are evident, master cylinder must be replaced. No abrasives, of any kind, are to be used on cylinder bore.

1. Lubricate new reservoir grommets with silicone brake lube and press into master cylinder. Make sure grommets are properly seated. Lay reservoir on flat, hard surface.
2. Rock master cylinder body onto reservoir until completely seated. Lubricate new piston seals and install on secondary piston, with lip of seals towards ends of piston. Install spring retainer.
3. Install secondary piston spring and secondary piston assembly in master cylinder. Lubricate primary piston seals with clean brake fluid.
4. Install primary piston in master cylinder. Press in piston and install snap ring. Fit diaphragm in reservoir cover and install cover.

Remove rubber boots from ends of cylinder. Remove piston return spring, cylinder cups, and pistons from cylinder. Remove bleeder screw and inspect bore for damage.

If bore of cylinder is pitted and/or scratched, hone or replace as needed. Soak rubber cylinder cups in brake fluid or assembly lube and reverse disassembly procedures.

Lateral Runout

Adjust wheel bearings until all end play is eliminated. Attach dial indicator with contact tip of indicator about 1" from rotor edge. Set indicator to zero and turn rotor through one complete revolution, noting indicator reading.

Parallelism

Check thickness of rotor at 4 or more points around circumference of rotor. Make all measurements at same distance from edge of rotor. If thickness variation is excessive, refinish or replace rotor as necessary.

TORQUE SPECIFICATIONS

TORQUE SPECIFICATIONS

DISC BRAKE SPECIFICATIONS

DISC BRAKE ROTOR SPECIFICATIONS

DRUM BRAKE SPECIFICATIONS

DRUM BRAKE SPECIFICATIONS

See also:
• ANTI-LOCK BRAKE SYSTEM
• SUSPENSION - FRONT (2WD)
• SUSPENSION - FRONT (2WD)
• HYDRO-BOOST BLEEDING
• BLEEDING SEQUENCE
• PARKING BRAKE - LEADING/TRAILING BRAKES
• TROUBLE SHOOTING
• MASTER CYLINDER PUSH ROD
• DISC CALIPERS & PADS - DELCO FLOATING CALIPER
• HYDRAULIC BRAKE BLEEDING