Suspension - Front (2wd) GMC Cab & Chassis R2500

DESCRIPTION

Independent front suspension consists of upper and lower control arms with steering knuckle mounted in between by ball joints. Control arms mount on inner pivot shafts by either rubber or threaded steel bushings. Coil springs are mounted between lower control arm and a formed seat in suspension crossmember. Some models have front suspension equipped with urethane air cylinders inside the coil springs.

Hydraulic or gas-charged shock absorbers fit between lower control arm and frame. A stabilizer bar is mounted to frame side rails and is connected to lower control arms by links.

WHEEL ALIGNMENT SPECIFICATIONS & PROCEDURES

See WHEEL ALIGNMENT SPECIFICATIONS & PROCEDURES in WHEEL ALIGNMENT section.

WHEEL BEARING ADJUSTMENT

1. Raise and support vehicle. Remove wheel cover, then spin wheel by hand to check bearings for excessive tightness, looseness, noise or roughness.
2. To check for tight or loose bearings, grip wheel assembly at top and bottom. Move assembly in and out while measuring hub movement. If movement is less than .0010" (.025 mm) or more than .0050" (.127 mm), adjust bearings. NOTE: Bearings should be cleaned, inspected, replaced (if necessary) and lubricated before adjustment.
3. With hub dust cap and cotter pin removed, tighten spindle bearing nut to 12 ft. lbs. (16 N.m) while turning wheel forward by hand. Back off nut until it is just loose.
4. Hand-tighten nut until snug, then loosen slightly (no more than 1/2 of a flat) until new cotter pin can be inserted. Hub play (in and out) should be .0010-.0050" (.025-.127 mm) when properly adjusted. Install dust cap and wheel cover.

Exploded View of Front Suspension Assembly G series front susp shown; C series similar (exc front susp struts). Courtesy of General Motors Corp. Scheme 1

Upper Ball Joint

1. Upper ball joint stud is spring-loaded in its socket to minimize looseness and compensate for normal wear. Raise vehicle and support at lower control arm. Remove front wheel assembly. Inspect ball joint stud for lateral shake or stud rotation in socket.
2. To check for lateral shake, grip hub assembly at top and bottom, then move spindle in and out. If stud has any lateral shake, replace ball joint. To check for stud movement, first remove stud nut, then detach steering knuckle from ball joint stud using ball joint separator.
3. With finger pressure only, attempt to twist stud in its socket. Replace ball joint if stud can be twisted. Inspect upper ball joint rubber grease seal for cuts or tears. Replace ball joint if damage is found.

Lower Ball Joint

1. Lower ball joints are a loose fit when not connected to steering knuckle. Wear may be checked without ball stud disassembly. To check lower ball joint, first lift vehicle.
2. Support weight of control arms at wheel and hub with jack stand. Measure distance between top of ball joint stud and tip of lower grease fitting. (Scheme 2) Move support to control arm and allow wheel and hub to hang free.
3. Remeasure distance. If difference exceeds.09" (2.38 mm), replace ball joint. Inspect lower ball joint rubber grease seal for cuts or tears. Replace ball joint if damage is found.

Checking Lower Ball Joint Wear Measurement Check diff in length betw loaded and unload ball joint; replace if meas is beyond spec. Courtesy of General Motors Corp. Scheme 2

REMOVAL & INSTALLATION

Note. Front wheel bearings should be cleaned, inspected, repacked and adjusted at every brake relining or 12,000 miles, whichever comes first.

WHEEL BEARINGS

1. Raise and support vehicle. Remove wheel and tire assembly. Detach dust cap and remove cotter pin. Detach brake caliper mounting bolts and hang caliper out of work area with wire. CAUTION: Do not hang brake caliper by flexible hose or severe hose damage can result.
2. Detach spindle nut, then remove hub and rotor assembly. Remove outer bearing from hub. Pry out inner grease seal and discard, then remove inner bearing. Wash bearings in cleaning solvent and inspect for cracked bearing cages and worn or pitted rollers.
3. Wash out hub and inspect bearing races for cracks, scoring or looseness in hub. If bearing(s) and/or race(s) need replacement, drive old race out of hub. Insert brass drift, through hub, behind race (in notches in hub). Using hammer, strike drift (alternating on each side of race) until race is removed.
4. Depending on vehicle, drive in new inner and/or outer race using a hammer and the proper bearing race installer. On vehicles with 1.75" (44.5 mm) diameter bearings, use Bearing Race Installer (J-8849 ); 1.94" (49.2 mm) diameter bearings use Bearing Race Installer (J-8457 ); 2.31" (58.7 mm) diameter bearings use Bearing Race Installer (J-8850 ) and 2.50" (63.5 mm) diameter bearings use Bearing Race Installer (J-8458 ).
5. Before installing, thoroughly pack each wheel bearing with GM Wheel Bearing Grease (1051344 ). With bearings and races replaced, install new inner grease seal (using a flat plate) until seal is flush with hub.
6. Lubricate seal lip (moderately) and hub cavity (liberally) with wheel bearing grease. To complete installation, reverse removal procedure, then adjust wheel bearings. See «ADJUSTMENTS & CHECKING»(/gmc/cab-chassis-r2500/1987-1987/remont/suspension-front/#suspension-front-2wd) .

Removal

Raise and support vehicle. If equipped, detach air shock pressure line fitting(s). Remove nuts and eye bolts securing upper and lower ends of shock absorber. Remove shock absorber from vehicle.

Installation

Position shock absorber over mounting bolts or into mounting brackets and install eye bolts. Tighten all bolts and nuts to specification. Lower vehicle.

1. Raise vehicle. Remove nuts and bolts attaching stabilizer bar brackets to frame. Remove bracket bolts and nuts at bushings on lower control arm.
2. Remove stabilizer bar from vehicle. Check all rubber bushings for excessive wear, damage or aging and replace as necessary.

Note. When installing, ensure slit in bar-to-frame bushing faces forward.

1. Lubricate bushings with rubber grease when installing on stabilizer bar. Position stabilizer bar on frame, then install frame brackets over bushings.
2. Install bracket mounting nuts and bolts loosely. Install brackets over bushings at lower control arms. Tighten all nuts and bolts to specification. Lower vehicle.

1. Raise vehicle and support under frame so that control arms hang free. Disconnect shock absorber and stabilizer bar bracket at lower control arm. Bolt Lower Control Arm Shaft Support (J-23028) onto a suitable jack, then position assembly under lower control arm shaft so shaft seats in grooves of support tool. (Scheme 3) CAUTION: Install a safety chain through lower control arm and coil spring before detaching lower control arm shaft bolts. Only control arm shaft and lower control arm hold spring in place once bolts are removed. Lower jack slowly.
2. Raise jack to relieve tension on lower control arm shaft, then remove 2 "U" bolts mounting control arm shaft to crossmember. Carefully lower jack until all tension is released from spring. If equipped with urethane air cylinder, deflate unit and remove from within spring, then remove spring from vehicle.

Front Coil Spring Removal Remove coil spring using a floor jack and Lower Control Arm Shaft Supp (J-23028). Courtesy of General Motors Corp. Scheme 3

Note. On models with urethane air cylinders within the coil springs, check for leaks and damage before installation. Air pressure in these cylinders may be increased or decreased (to adjust vehicle trim) through valve located at bottom of cylinder.

To install coil spring (and air cylinder if equipped), reverse removal procedure. When positioning lower control arm shaft to crossmember, ensure front indexing hole in shaft is aligned with crossmember attaching saddle stud. Install and tighten all mounting bolts. Remove support tool and safety chain, then lower vehicle.

STEERING KNUCKLE

Note. Support front of vehicle with twin-post hoist so front coil spring remains compressed and steering knuckle accessible. If using frame hoist, support lower control arm with adjustable jack stand to safely retain spring in its curb height position.

1. Raise and support vehicle. Remove wheel and tire assembly. Detach brake caliper mounting bolts and wire caliper aside. Remove hub and brake rotor assembly. Remove rotor splash shield.
2. Remove outer tie rod end ball stud cotter pin and nut. Remove stud from steering knuckle arm by striking arm (at tie rod end) with hammer while using heavy hammer as a backing. Pull tie rod end stud from arm.
3. Remove upper and lower ball joint cotter pins and loosen nuts. Using Ball Joint Separator (J-23742 ), free steering knuckle from ball joint studs. (Scheme 4) Remove stud nuts and withdraw steering knuckle.

Inspection

With ball joints and tie rod end detached, clean all dirt from steering knuckle. Inspect tapered holes in knuckle for out-of-round, deformation or damage. Replace steering knuckle if any of these conditions exist.

To install, reverse removal procedure and tighten all nuts and bolts. If necessary, tighten ball joint and/or tie rod end stud nut one more notch to insert cotter pin. After installation, adjust wheel bearings as necessary. See ADJUSTMENTS & CHECKING .

1. Raise and support vehicle. If frame hoist is used, support lower control arm with adjustable jack stand. Remove cotter pin from upper ball stud. Loosen nut 2 turns (but do not remove at this time).
2. Remove brake caliper and suspend it from frame with wire. Do not hang caliper by flexible brake hose. Install Ball Joint Separator (J-23742 ) between the ball studs. (Scheme 4)
3. Extend bolt on separator tool to loosen ball stud from knuckle. Remove separator tool and stud nut. Center punch rivet heads, then drill out rivets and remove ball joint assembly.

1. To install, reverse removal procedure. Using new nuts and bolts in place of rivets to attach new ball joint to control arm, tighten to specification.
2. Install new cotter pin, tightening nut as necessary to align stud hole. Install grease fitting and lubricate new ball joint with chassis lubricant equal to GM-6031-M Chassis Grease (1051344 ).

Note. Lubricate ball joints (and tie rod ends) every 4 months or 5000 miles on C20 and G30 models and every 12 months or 5000 miles on all other vehicles. For severe driving conditions, lubricate every 3 months or 2500 miles on all models.

Scheme 4

1. Raise and support vehicle. If frame hoist is used, support lower control arm with adjustable jack stand. Remove wheel and tire assembly. Remove lower ball joint stud cotter pin. Loosen stud nut 2 turns but do not remove at this time.
2. Remove brake caliper and suspend out of way with wire. Do not hang by flexible brake hose. Install Ball Joint Separator (J-23742 ) between the ball studs. Extend bolt on separator tool to loosen ball stud. (Scheme 4) (Scheme 4): Separating Upper & Lower Ball Joints Ensure the sep tool is placed in the proper pos depending on the ball joint being separated. Courtesy of General Motors Corp.
3. Remove tool and ball stud nut. Pull brake rotor/hub assembly and steering knuckle assembly up off ball stud and support upper control arm with block of wood.
4. Install Ball Joint Remover and Installer Set (J-9519-D, which must include "C" Clamp J-9519-10, Installer J-9519-9, Adapter J-9519-16 and Receiver J-9519-22 or J-21474-13 ). Turn hex head screw on clamp to press lower ball joint out of control arm bore. Remove tools and ball joint from vehicle. (Scheme 5)

Scheme 5

1. Start new ball joint in control arm bore, then install ball joint remover and installer set. (Scheme 5) Ensure bleed vent in rubber boot is positioned facing forward. (Scheme 5): Removing & Installing Lower Ball Joint Turn hex head screw on clamp until ball joint is either rem from or seated in control arm bore. Courtesy of General Motors Corp.
2. Turn hex head screw on clamp until ball joint is seated in control arm. Reverse removal procedure to complete installation. Install new cotter pin, tightening nut as necessary to align stud hole. Install grease fitting and lubricate new ball joint with chassis lubricant equal to GM-6031-M Chassis Grease (1051344 ).

1. Raise and support vehicle. If frame hoist is used, support lower control arm with adjustable jack stand. Remove wheel and tire assembly. On C10 and G10/20 models (with rubber bushings), remove cotter pin from upper ball joint and loosen nut.
2. Remove brake caliper and suspend out of way. Do not hang by brake hose. Using Ball Joint Separator (J-23742 ), loosen ball joint stud from steering knuckle. Remove tool and ball joint nut, then raise control arm to clear steering knuckle.
3. Detach nuts and bolts attaching control arm shaft to frame member, then remove control arm from vehicle. Tape shims together and tag for proper location when control arm is reinstalled.
4. On C20/30 and G30 models (with steel bushings), loosen upper control arm shaft end nuts before loosening shaft-to-frame attaching nuts. Loosen shaft-to-frame nuts and remove caster and camber shims. Tape shims together and tag for proper location when control arm is reinstalled.
5. Detach pivot shaft-to-frame nuts but do not allow control arm to swing too far away from frame. Use a safety chain to retain control arm in close relationship to frame. Detach shaft end nuts and remove shaft from control arm.

Scheme 6

1. Mount control arm assembly in a vise. Install Front Control Arm Bushing Service Set (J-24435 which must include "C" Clamp J-24435-7, Adapter J-24435-1, Receiver J-24435-3, Installer J-24435-4 and Adapter J-24435-5 ) onto control arm bushing using "C" clamp and proper adapters. (Scheme 6)
2. Tighten clamp to draw out old bushing, then discard bushing. Remove pivot shaft from control arm if necessary. Reposition control arm in vise and remove opposite side bushing.
3. Lubricate new bushing with rubber grease and position into control arm bore. Install "C" clamp and proper adapters over bushing, then tighten clamp to press bushing into position. (Scheme 6) (Scheme 6): Upper Control Arm Rubber Bushing Replacement Tighten hex head on clamp to draw out old bushing, then reverse procedure to install new bushing. Courtesy of General Motors Corp.
4. Install pivot shaft into inside diameter of first installed bushing. Install remaining bushing as described in step 3). Remove bushing service tools and install control arm on vehicle. Tighten all fasteners to specification.

Inner Pivot Shaft & Bushing Replacement (C20/30 & G30 With Steel Bushings)

1. Remove grease fittings from bushing outer ends and unscrew bushings from control arm and shaft. Remove and discard old seals. Slide new seal onto each end of shaft and insert shaft into control arm.
2. Adjust shaft until centered in control arm, then turn bushings in and tighten to specification. (Scheme 7) Check shaft for free rotation. Install grease fittings and lubricate with proper chassis grease. CAUTION: When installing upper control arm, ensure special aligning washers are positioned onto pivot shaft with concave and convex sides together.

Scheme 7

1. Place control arm in position on bracket and install mounting nuts. On C10 and G10/20 models (with rubber bushings), before tightening nuts, insert caster and camber shims in the same order as removed. Tighten mounting nuts to specification. NOTE: A normal shim pack will leave at least 2 bolt threads exposed beyond the nut. If 2 threads cannot be obtained, check for damaged control arms and related parts. The difference between front and rear shim packs must be no more than.30" (7.62 mm). The front shim pack must be at least.24" (6.09 mm) thick. Always tighten thinner shim pack's nut first for improved shaft-to-frame clamping force and torque retention.
2. On C20/30 and G30 models (with steel bushings), position pivot shaft-to-frame bolts and start pivot shaft nuts. Tighten shaft end nuts. Check for proper spacing. (Scheme 7) The shaft should rotate by hand after tightening nuts. (Scheme 7): Pos Upper Control Arm Pivot Shaft (With Steel Bushings) Ensure shaft rotates by hand after end nuts are tightened. Courtesy of General Motors Corp.
3. Install caster and camber shims in the same order as removed and tighten pivot shaft-to-frame mounting nuts. Remove safety chain and install wheel and tire assembly. Lower vehicle.
4. On C10 and G10/20 models, insert ball joint stud into steering knuckle and install nut. Tighten stud nut to specification and install new cotter pin. To complete installation, reverse removal procedure. After installation, check front end alignment.

1. Raise vehicle and place safety stands under frame side rails. Remove wheel and tire assembly. Remove brake caliper and suspend out of way with wire. Do not hang from flexible brake hose. Remove coil spring. See «COIL SPRINGS»(/gmc/cab-chassis-r2500/1987-1987/remont/suspension-front/#suspension-front-2wd) . Support inboard end of control arm after spring removal. NOTE: On C10 models (with rubber bushings) and C20/30 and G30 models (with steel bushings), if just control arm bushings or pivot shaft are to be replaced, lower control arm does not have to be removed from vehicle.
2. Remove cotter pin from lower ball joint stud, then loosen stud nut 1 turn. Using Ball Joint Separator (J-23742 ), position large cupped end of tool over upper ball stud nut and pilot threaded end of tool onto lower ball stud.
3. Extend bolt of tool to loosen ball stud from steering knuckle, then remove tool and stud nut. Detach nuts attaching control arm to frame, then lower jack stand and remove control arm from vehicle.

Inner Pivot Shaft & Bushings Replacement (G10/20 With Rubber Bushings)

1. With lower control arm removed from vehicle, detach pivot shaft nuts. Place control arm in an arbor press. Press front end of pivot shaft to remove rear bushing and pivot shaft assembly.
2. Using Lower Control Arm Bushing Stake Remover (J-22717 ), remove stakes on front bushing. Using "C" Clamp (J-24435-7 ), Receiver (J-24435-3 ), Remover (J-24435-2 ) and Spacer (J-24435-6 ), tighten hex head on "C" clamp to press out old bushing.
3. Install new front bushing using "C" clamp, spacer and Installer (J-24435-4 ). Ensure outer tube hole is to the front (or forward to the staked bushing) and spacer is between parallel sides of control arm bushing bore. (Scheme 8) Stake front bushing in at least 2 places after installation. Insert pivot shaft and second bushing.

Scheme 8

1. Raise vehicle on hoist and support frame so control arms hang free. Position adjustable jack stand under lower control arm, inboard of spring, and into control arm depression.
2. Install safety chain over upper control arm, inboard of stabilizer and outboard of shock absorber. Disconnect shock and stabilizer bar attachments at lower control arm. Loosen shaft end nuts.
3. Detach "U" bolts retaining inboard end of lower control arm. Lower jack SLOWLY to release spring tension and gain clearance to remove bushings. Ensure all tension is released from spring before proceeding.
4. Using Lower Control Arm Bushing Stake Remover (J-22717 ), remove stakes on front bushing. Using Front Control Arm Bushing Service Set (J-24435, which must include "C" Clamp J-24435-7, Remover J-24435-2, Receiver J-24435-3, Installer J-24435-4 and Spacer J-24435-6 ), tighten hex head on "C" clamp to remove old bushings. (Scheme 8)
5. Remove tools and discard old bushing. Remove stakes on opposite side bushing, then install remover tools and press out bushing (leave pivot shaft in to guide tool). Remove pivot shaft if necessary.
6. Coat each new bushing with rubber grease before installation. Position 1 bushing in control arm bore. Install "C" clamp and proper service tools, then press bushing into position until seated firmly in control arm. (Scheme 8) Insert pivot shaft, then install second bushing. (Scheme 8): Lower Control Arm Rubber Bushing Replacement Ensure Spacer (J-24435-6) is in position as shown to avoid collapsing control arm during assembly. Courtesy of General Motors Corp.
7. Stake front bushing in at least 2 places after installation. To complete installation, reverse removal procedure. Tighten all fasteners to specification. After installation, check front end alignment as needed.

Scheme 9

1. Raise vehicle on hoist and support frame so control arms hang free. Position adjustable jack stand under lower control arm, inboard of spring, and into control arm depression.
2. Install safety chain over upper control arm, inboard of stabilizer and outboard of shock absorber. Disconnect shock absorber attachments at lower control arm. Loosen shaft end nuts.
3. Remove "U" bolts. Lower jack stand just enough to gain access to pivot shaft. Detach shaft end nuts and remove shaft. Remove grease fittings from ends of bushings, then unscrew bushings from shaft and control arm. Remove shaft and discard seals.
4. Slide new seal onto each end of shaft and insert shaft into control arm. Start new bushings on shaft and into control arm. Adjust shaft until it is centered in control arm. (Scheme 9) Once centered, turn bushings in and tighten to specification. Check shaft for free rotation. Install grease fittings and lubricate bushings. (Scheme 9): Positioning Lower Control Arm Pivot Shaft (W/ Steel Bushings) Depend on the pivot shaft & bushing config, pos pivot shaft as shown. Courtesy of General Motors Corp.
5. Install shaft end nuts but do not tighten at this time. Raise jack and position shaft into crossmember saddle. Ensure hole in shaft is indexed to mate with bolt head in saddle.
6. Install "U" bolts but do not tighten nuts at this time. Tighten pivot shaft end nuts. Ensure shaft rotates by hand after tightening. Tighten "U" bolt nuts. Remove safety chain and lower vehicle.

1. If removed, place control arm in position and install ball joint stud into steering knuckle bore. Tighten stud nut to specification and install new cotter pin. Install coil spring and control arm.
2. To complete installation, reverse removal procedure. Tighten all nuts and bolts to specification and check wheel alignment as necessary. See «WHEEL ALIGNMENT»(/gmc/cab-chassis-r2500/1987-1987/remont/suspension-front/#suspension-front-2wd__wheel-alignment-specifications-procedures) section for procedures and specifications.

CROSSMEMBER & SUSPENSION UNIT

Note. Front suspension components may be serviced separately as previously outlined or, if extensive repairs are needed, crossmember and suspension unit can be removed as an assembly.

1. Raise hood and disconnect negative battery cable. Raise and support vehicle on twin-post hoist. Remove both front wheel and tire assemblies. Disconnect front brake hose clip from each upper control arm.
2. Support front of vehicle with jack stands at frame side rails and lower front hoist. Clean area around front brake hose fittings, then detach hoses from calipers and plug openings.
3. Disconnect tie rod ends from steering knuckles. Disconnect front stabilizer bar (if equipped) and shocks from lower control arms. Remove brake line clip bolts from front suspension crossmember. On "C" models, the clip is located under right side engine mount support bracket. CAUTION: Brake line clips must be disconnected from front suspension unit or severe damage to brake line will result when unit is lowered from vehicle.
4. Detach engine mount support bracket-to-front suspension crossmember bolts. (Scheme 10) Detach crossmember-to-lower frame rail bolts. Raise front hoist to support front suspension member. Support engine. NOTE: Engine must be supported adequately before front suspension unit is lowered from vehicle.
5. Detach upper control arm bracket-to-frame side rail bolts. Suspension unit is now disconnected from vehicle. Lower front hoist to lower front suspension unit from vehicle.

Scheme 10

1. With front suspension unit positioned on hoist, raise hoist to align unit with frame rail holes. Assemble upper control arm bracket bolts and crossmember bolts to frame rails finger tight. NOTE: Control arm bracket bolts must be tightened before crossmember bolts. Ensure crossmember is in contact with frame side rails.
2. Tighten upper control arm bracket bolts to frame side rails. Remove engine support at this time and lower hoist. Assemble engine mount support bracket-to-front suspension crossmember bolts and tighten to specification. To complete installation, reverse removal procedure. Lubricate suspension components. Bleed brake system.

TORQUE SPECIFICATIONS

TORQUE SPECIFICATIONS

See also:
• ADJUSTMENTS & CHECKING
• WHEEL ALIGNMENT