Drive Axle - 4wd Front GMC Cab & Chassis R2500

AXLE RATIO & IDENTIFICATION

To determine drive axle ratio, see DRIVE AXLE RATIO IDENTIFICATION article in this section.

DESCRIPTION

Chevrolet and GMC "S" series 4WD models use an independent front drive axle with an automatic engagement system. It consists of a transfer case with a synchronized input shaft, and a front axle unit with central locking clutch and vacuum operated cable shift control.

REMOVAL & INSTALLATION

For removal, installation and overhaul of drive axles, see AXLE SHAFTS - FRONT in this section.

Scheme 11

1. Disconnect negative battery cable. Remove shift cable from vacuum actuator by disengaging lock spring. Push in actuator diaphragm to release cable.
2. Unlock steering wheel. Raise and support vehicle. Remove front wheels, engine drive belt shield and front axle skid plate (if equipped).
3. Place a support under right lower control arm and disconnect right upper ball joint. Remove support so control arm can hang free. Disconnect right drive axle shaft from differential output shaft. Keep axle from turning by inserting a drift through opening on top of brake caliper into a vane of brake rotor.
4. Remove 4WD indicator light connection from switch. Remove 3 bolts securing cable and switch housing. Pull housing away to gain access to cable locking spring. DO NOT unscrew cable coupling nut unless cable is being replaced. See «SHIFT CABLE»(/gmc/cab-chassis-r2500/1987-1987/remont/differentials-drive-axles/#drive-axle-4wd-front) removal.
5. Disconnect shift cable from shift fork shaft by lifting spring over slot in shift fork. Remove 2 bolts securing tube bracket to frame bracket and remove remaining 2 bolts securing tube assembly to carrier.
6. Remove tube assembly by working around drive axle. DO NOT allow sleeve, thrust washers, connector and output shaft to fall out of carrier while removing tube. NOTE: Align notch with tab on washer.

Scheme 12

1. Install sleeve, thrust washers, connector and output shaft in carrier. Apply Loctite (514) on axle tube to differential surface. Be sure to install thrust washer with notch aligned with tab on washer. (Scheme 11)
2. Install tube and shaft assembly to differential and install one bolt at one o'clock position but DO NOT tighten. Pull assembly down and install cable, switch housing and remaining 4 bolts. Tighten bolts to specification.
3. Install and tighten 2 bolts securing tube to frame. Check shift unit operation. To complete installation, reverse removal procedure.

Removal

1. Disengage shift cable from vacuum actuator by disengaging locking spring. Push actuator diaphragm in to release cable. Squeeze 2 locking fingers of cable with pliers. Pull cable out of bracket hole. (Scheme 13)
2. Raise and support vehicle. Remove 3 bolts securing cable and switch housing to carrier. DO NOT unscrew coupling nut at this time. Remove shift cable housing from carrier assembly. Pull out about 3/4" of cable. Remove cable end from shift fork shaft. Bend tang of locked spring, then pull cable end from shift fork shaft.
3. Unscrew coupler nut and remove shift cable from shift cable housing. Remove cable from vehicle.

Scheme 13

1. Install cable using proper routing. (Scheme 13) Install cable and switch housing to carrier using 3 attaching bolts. Tighten mounting bolts to 30-40 ft. lbs. (40-55 N.m).
2. Guide cable though switch housing into fork shaft hole and push cable in. Cable will snap into place. Start turning coupling nut by hand to avoid cross threading. Tighten nut to 90 INCH lbs. (10 N.m). DO NOT overtighten nut.
3. Connect shift cable to vacuum actuator by pressing cable into bracket hole. Cable and housing will snap into place. Check cable operation. NOTE: Mount cable before routing.

Remove pilot bearing using Output Shaft Pilot Bearing Remover (J-34011). Install new pilot bearing using Output Shaft Pilot Bearing Installer (J-33842).

Scheme 14

Scheme 15

Scheme 16

1. Remove axle output shaft and thrust washer. Remove left output shaft by prying between shaft flange and carrier bolt head with a screwdriver and simultaneously striking shaft flange with a soft-faced hammer.
2. Remove 6 cover-to-carrier bolts securing left side. Tap cover to loosen and remove. While supporting cover, drive out left seal using a punch.
3. Remove 10 bolts holding axle housing halves together. Insert screwdriver in slots provided and pry axle housing halves apart. (Scheme 14) NOTE: Pry only at these points.
4. Remove differential from housing. Remove both side bearing adjusting locks. Remove race for both differential side bearings by turning side bearing adjusting sleeve with Side Bearing Adjuster Wrench (J-33792) until race is pushed out of carrier.
5. Using Pinion Flange Holder (J-8614-01), remove pinion flange nut. Install Pinion Bearing Remover/Installer (J-33837). Use bolts supplied with tool to install fixture on carrier and remove pinion and flange. (Scheme 15)
6. Install Bearing Race Remover (J-33837-6) on Holding Fixture (J-33837-1) and remove outer pinion bearing, race and pinion seal. (Scheme 16)
7. Remove inner pinion bearing race by pushing it out of housing with bearing race remover installed on Pinion Bearing Remover/Installer (J-33837). Remove inner drive pinion bearing using Differential Side/Pinion Bearing Remover (J-22912-01).

Cleaning & Inspection

Clean all parts in cleaning solvent. Inspect all parts for excessive wear.

Scheme 17

1. Lubricate outer pinion and inner bearing races. Install using Holding Fixture (J-33837-1) and Bearing Race Installer (J-33837-4) until races are seated in housing. Lubricate inner and outer bearings, then set pinion depth. See «ADJUSTMENTS»(/gmc/cab-chassis-r2500/1987-1987/remont/differentials-drive-axles/#drive-axle-4wd-front). (Scheme 17)
2. Install inner pinion bearing on shaft using Pinion Bearing Installer (J-33785). Install new collapsible spacer on pinion shaft and position assembly in carrier. Lubricate outer pinion bearing and install in housing. NOTE: Ensure races are properly seated.
3. Lubricate pinion bearing seal with axle lube. Using Pinion Seal Installer (J-33782), install seal. Install pinion flange, washer and nut.
4. Install Flange Holder (J-8614-01) on pinion flange and hold flange while tightening pinion flange nut. Tighten nut until no end play is present. DO NOT tighten further as preload specifications are being approached. For preload, See «DRIVE PINION DEPTH»(/gmc/cab-chassis-r2500/1987-1987/remont/differentials-drive-axles/#drive-axle-4wd-front__drive-pinion-depth) under ADJUSTMENTS. NOTE: After preload has been checked, final tightening should be done very carefully. If preload was 5 INCH lbs. (.6 N.m), any additional tightening of pinion nut can add many additional INCH lbs. of torque. Check preload after each slight amount of tightening.
5. Rotate pinion several times to ensure bearings have been seated. Set final preload to 15-25 INCH lbs. (1.7-2.8 N.m).
6. Assemble output shaft bearings and adjusting sleeves into inserts in carrier and finger tighten. Install differential side bearing race into housing using Differential Side Bearing Race Installer (J-23423-A).
7. Using new output shaft bearings, adjusting sleeve inserts and Output Shaft Bearing Installer (J-33788), press output shaft bearings into adjusting sleeves from inner side of sleeves.
8. Install adjusting sleeve and bearing into insert and finger tighten. Use a Differential Side Bearing Race Installer (J-23423-A) and press assembly into axle housing.
9. Install differential into housing and set backlash adjustment to specification. See «ADJUSTMENTS»(/gmc/cab-chassis-r2500/1987-1987/remont/differentials-drive-axles/#drive-axle-4wd-front).
10. Install left differential housing seal. Support housing to prevent distorting or bending of housing. Apply gasket sealer to housing surface and install housing cover. Tighten nuts to specification.

Disassembly

1. Remove side bearings using Differential Side/Pinion Bearing Remover (J-22912-01). Remove pinions, side gears and thrust washers from housing. Mark side gears and housing so they can be installed in original location.
2. If ring gear is to be replaced and is tight on housing after removing right-hand thread bolts, drive off ring gear using a brass drift and hammer. DO NOT pry between ring gear and housing.

Reassembly

1. Lubricate all parts with axle lubricant. Place side gear thrust washers over side gear hubs. Install side gears in housing. Ensure any original parts are installed in original positions.
2. Position a pinion (with washer) between side gears and rotate gears until pinion is directly opposite opening in housing. Place other pinion between side gears so pinion shaft holes align. Rotate gears to make sure holes in pinions will line up with holes in housing.
3. If holes line up, rotate pinions back toward opening just enough to permit sliding in pinion thrust washer. Install 2 new bolts into opposite sides of ring gear, then install ring gear on housing. Tighten ring gear bolts.

DRIVE PINION DEPTH

Note. All "S" series 4WD front wheel drive pinions are "nominal" or "zero" and not marked. Shim thickness will equal dial indicator gauge reading.

Scheme 18

1. Lubricate inner and outer pinion bearings liberally with axle lubricant. Hold pinion bearings in position and install Pinion Shim Setting Gauge (J-33838). With gauge installed, preload inner and outer pinion bearing to 15-25 INCH lbs. (2-3 N.m) by tightening mounting bolt while holding end of gauge shaft with a wrench.
2. Using Dial Indicator (J-29763), set reading to zero, then position dial indicator on pinion shim setting gauge. Push dial indicator downward until needle rotates approximately 3 turns clock- wise. Tighten dial indicator in this position. (Scheme 18)
3. Set button of pinion shim setting gauge on differential bearing bore. Rotate gauge slowly back and forth until dial indicator reads lowest point of bore. Set dial indicator to zero. Repeat rocking action of gauge to verify zero setting.
4. After zero setting is obtained and verified, move gauge button out of differential side bearing bore. Record dial indicator reading. Use a shim that is exactly the same size as indicator reading.
5. Remove dial indicator and gauge from carrier. Position correct shim on drive pinion. Install drive pinion.

Scheme 19

Scheme 20

1. Using Side Bearing Adjusting Wrench (J-33792), turn in left adjusting sleeve toward differential housing until backlash is felt between ring and pinion gears.
2. Ensure carrier mating surfaces are clean. Assemble carrier together without using sealer. If axle housing halves will not make complete contact, back out right adjusting sleeve.
3. Install 4 axle housing bolts and tighten to 37 ft. lbs. (50 N.m). Using side bearing adjusting wrench, tighten right adjusting sleeve until no backlash is present, which is approximately 100 ft. lbs. (140 N.m). (Scheme 19)
4. Mark location of adjusting sleeves in relation to carrier halves, so notches in adjusting sleeves can be counted when turned. Turn right adjusting sleeve out 2 notches using side bearing adjusting wrench. Turn in left adjusting sleeve one notch. (Scheme 20)
5. Rotate axle housing several times to seat bearings, mount dial indicator. Use a small button on indicator stem so contact can be made near heel end of tooth angle for accurate backlash read- ing. Set backlash to specification. See «AXLE ASSEMBLY SPECIFICATIONS»(/gmc/cab-chassis-r2500/1987-1987/remont/differentials-drive-axles/#drive-axle-4wd-front) table.
6. If backlash is not within specification, readjust adjusting sleeves as necessary. DO NOT install adjusting sleeve locks at this time.
7. Mark right adjusting sleeve so it can be repositioned in same location and loosen sleeve to release right side bearing to differential housing contact. Remove 4 axle housing bolts and axle housing half. Apply Loctite (514) on one axle housing surface.
8. Reinstall axle housing halves. Install 10 attaching bolts and tighten to specification. Reposition right adjusting sleeve in previous marked position and install both adjusting sleeve locks.
9. Perform gear tooth contact pattern check. See «GEAR TOOTH CONTACT PATTERNS»(/gmc/cab-chassis-r2500/1987-1987/remont/drivelineaxles/#gear-tooth-contact-patterns-general-information) article in this section. AXLE ASSEMBLY SPECIFICATIONS Application Specifications Ring Gear Backlash Runout.003" (.08 mm) Ring Gear Backlash.003-.010" (.08-.25 mm) INCH Lbs. (N.m) Pinion Bearing Preload 15-25 (1.7-2.8)

TORQUE SPECIFICATIONS

TORQUE SPECIFICATIONS

See also:
• DRIVE AXLE RATIO IDENTIFICATION
• AXLE SHAFTS - FRONT
• GEAR TOOTH CONTACT PATTERNS
• SHIFT CABLE
• DRIVE PINION DEPTH