Drive Axle - Front GMC S15 Pickup

IDENTIFICATION

To determine the specific drive axle ratio, refer to the below DRIVE AXLE RATIO IDENTIFICATION article in this section.

DESCRIPTION

Chevrolet and GMC "S" series 4WD models use an independent front drive axle with a vacuum actuation 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.

The vacuum actuation system consists of a vacuum switch and vacuum actuator. (Scheme 1) The shift mechanism in transfer case triggers vacuum switch to apply engine vacuum to vacuum actuator, after about a 3 second delay. The vacuum actuator, in turn, pulls on shift cable which pulls on shift fork in axle. This connects the right axle output shaft to the front axle differential. Torque is now available to front wheels.

Scheme 1

Removal & Installation

1. Raise and support vehicle on safety stands. Remove wheel and brake caliper and flex hoses at brackets. Remove tie rods at steering knuckle using Puller (J-24319). Remove shock lower bolts and push shocks out of way.
2. Remove drive axle-to-axle tube bolts. Remove axle shaft cotter pin, nut and washer. Position inner part of drive axle forward and support away from frame. Remove shaft from hub using Puller (J-28733). Remove axle shaft from vehicle.
3. Install axle shaft into hub. Tighten nut and washer to specifications. Install retainer and install cotter pin. To complete installation, reverse removal procedure.

Scheme 2

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.
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/s15-pickup/1987-1991/remont/differentials-drive-axles/#drive-axle-front) removal.
5. Disconnect shift cable from shift fork shaft by lifting spring over slot in shift fork. Remove bolts securing tube bracket to frame bracket. Remove 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. (Scheme 2)

Scheme 3

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 3)
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.
2. Raise and support vehicle. Remove 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. Note cable routing for installation. Unscrew coupler nut and remove shift cable from shift cable housing. Remove cable from vehicle.

Installation

1. Install cable and switch housing to carrier. 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 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.

Disconnect vacuum line from actuator. Remove shift cable. See SHIFT CABLE . Remove vacuum actuator bolts and actuator. To install, reverse removal procedure.

Remove right extension tube and inner axle shaft. Refer to the RIGHT AXLE TUBE & INNER SHAFT . Remove pilot bearing using Output Shaft Pilot Bearing Remover (J-34011). Install new pilot bearing using Output Shaft Pilot Bearing Installer (J-33842). To complete installation, reverse removal procedure.

1. Raise and support vehicle. Remove right extension tube and inner axle. See «RIGHT AXLE TUBE & INNER SHAFT»(/gmc/s15-pickup/1987-1991/remont/differentials-drive-axles/#drive-axle-front) .
2. Remove steering stabilizer and idler arm bolts at vehicle frame. Pull steering linkage forward. Remove axle vent hose.
3. Remove inner attaching bolts for the left drive axle. Match mark front drive shaft and remove bolts and clamps.
4. Working through hole in frame, remove axle-to-frame mounting bolts. Tip axle assembly counterclockwise while lifting to gain clearance from mounting ears and remove axle assembly.
5. To install, reverse removal procedure. Tighten all bolts and nuts to specification. See «TORQUE SPECIFICATIONS»(/gmc/s15-pickup/1987-1991/remont/differentials-drive-axles/#drive-axle-front) table.

Scheme 4

1. Using side cutter pliers, cut dust boot band clamps. (Scheme 4) Pull boot from tri-pot housing and separate tri-pot housing from spider assembly. Wrap tape around spider assembly to retain needle bearings.
2. Using snap ring pliers, remove axle shaft retaining ring and separate spider assembly from axle shaft. Note position of counterbore of spider for reassembly purposes. Remove spacer ring if necessary. Slide dust boot from axle shaft.

Disassembly (Outer CV Joint)

1. Using side cutter pliers, cut dust boot clamps. Pull boot back from CV joint. Using Snap Ring Pliers (J-8059), spread retaining ring ears apart and pull axle shaft out of CV cage.
2. Using a brass drift and hammer, gently tap on cage until its tilted enough to remove the first ball. Repeat procedure to remove the remaining balls. Rotate inner race at a 90 degree angle to cage and remove race. (Scheme 5)

Cleaning & Inspection

Wash all parts in solvent and dry with compressed air. Inspect all parts for excessive wear and scoring. Inspect splined stub shaft for wear, cracks and twisted splines.

Scheme 5

Reassembly (Inner CV Joint)

1. Flush grease from tri-pot housing. Repack housing using half of grease supplied in dust boot kit. Place the remainder of grease into dust boot after securing small band clamp.
2. Position small band clamp to dust boot. Slide boot onto axle shaft. Ensure boot seats into groove on axle shaft and secure clamp using side cutter pliers. Install spacer ring, if previously removed. Ensure ring seats into groove properly.
3. Install spider with counterbore facing end of axle shaft. Install snap ring to retain spider assembly. Position large band clamp onto dust boot. Coat inner lip with grease and seat boot into groove on tri-pot housing. Secure band clamp. Reverse disassembly procedures to complete reassembly.

Scheme 6

1. Flush grease from joint and repack with half of grease provided in dust boot kit. Place the remainder of grease into dust boot after securing small band clamp.
2. Apply a light coat of CV grease on ball grooves of inner race and cage. Install inner race into cage. Pivot cage at a 90 degree angle to center line of outer race with cage windows aligned with lands of outer race. NOTE: Ensure retaining ring side of inner race faces axle shaft.
3. Install ball bearings one at a time into outer CV joint as cage is tilted and rotated. After balls are installed into cage, pivot cage and inner race into installed position.
4. Position band clamp onto boot and slide boot onto axle shaft. Secure clamp using side cutter pliers. Coat inside lip (large diameter end of seal with CV grease) and slide large band clamp onto dust boot.
5. Install snap ring onto axle shaft, and slide CV joint onto axle shaft until snap ring seats in groove. Slide dust boot toward joint until dust boot is in the groove in the axle shaft. Secure large band clamp. Reverse disassembly procedure to complete reassembly. (Scheme 6)

Scheme 7

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, (one next to fill plug, and 180 degrees from fill plug) and pry axle housing halves apart.
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 Holding Fixture (J-33837-1). Use bolts supplied with tool to install fixture on carrier and remove pinion and flange. (Scheme 7)
6. Install Bearing Race Remover (J-33837-6) on Holding Fixture (J-33837-1) and remove outer pinion bearing, race and pinion seal. (Scheme 8)
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).

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

Scheme 8

Scheme 9

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. (Scheme 9) Lubricate inner and outer bearings, then set pinion depth. See «DRIVE PINION DEPTH»(/gmc/s15-pickup/1987-1991/remont/differentials-drive-axles/#drive-axle-front) under ADJUSTMENTS.
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.
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 procedure, See «DRIVE PINION DEPTH»(/gmc/s15-pickup/1987-1991/remont/differentials-drive-axles/#drive-axle-front) under ADJUSTMENTS.
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. Using Differential Side Bearing Race Installer (J-23423-A), press assembly into axle housing.
9. Install differential into housing and set ring gear backlash adjustment to specification. See «RING GEAR BACKLASH»(/gmc/s15-pickup/1987-1991/remont/differentials-drive-axles/#drive-axle-front) under ADJUSTMENTS.
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.

Disassembly

1. Using Differential Side/Pinion Bearing Remover (J-22912-01), remove side bearings. Remove pinion shaft lock screw and pinion. 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. Rotate pinions back toward opening just enough to permit sliding in pinion gear thrust washer. Install pinion shaft and lock screw. Install 2 new bolts into opposite sides of ring gear, then install ring gear on housing. Tighten ring gear bolts. Refer to «TORQUE SPECIFICATIONS»(/gmc/s15-pickup/1987-1991/remont/differentials-drive-axles/#drive-axle-front) table.

Scheme 10

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. (1.7-2.8 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 clockwise. Tighten dial indicator in this position. (Scheme 10) NOTE: All "S" series 4WD front axle drive pinions are "nominal" or "zero" and not marked. Shim thickness will equal dial indicator gauge reading.
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 11

Scheme 12

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 11)
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 12)
5. Rotate axle housing several times to seat bearings, then mount dial indicator. Use a small button on indicator stem so contact can be made near heel end of tooth angle for accurate backlash reading. Set backlash to the correct specification. Refer to the correct «AXLE ASSEMBLY SPECIFICATIONS»(/gmc/s15-pickup/1987-1991/remont/differentials-drive-axles/#drive-axle-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/s15-pickup/1987-1991/remont/drivelineaxles/#gear-tooth-contact-patterns-general-information) article in this section. AXLE ASSEMBLY SPECIFICATIONS Application In. (mm) Ring Gear Backlash.003-.010 (.08-.25) Ring Gear Backlash Runout.003 (.08) INCH Lbs. (N.m) Pinion Bearing Preload 15-25 (1.7-2.8)

TORQUE SPECIFICATIONS

TORQUE SPECIFICATIONS

See also:
• DRIVE AXLE RATIO IDENTIFICATION
• GEAR TOOTH CONTACT PATTERNS
• SHIFT CABLE