Differential - Locking GMC Cab & Chassis R3500

AXLE RATIO & IDENTIFICATION

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

ONE-PIECE CASE

Eaton one-piece case locking differential is a 2-pinion type with a clutch disc pack behind each side gear. The unit also utilizes a speed-sensitive device which automatically locks both rear wheels if either wheel should spin excessively during slow vehicle operation.

TWO-PIECE CASE

Eaton two-piece locking differential is a 3-pinion type with clutch disc packs behind both side gears. The unit also utilizes a speed-sensitive device which automatically locks both rear wheels if either wheel should spin excessively during slow vehicle operation.

Note. Some components may not be used with all ring gears.

TESTING

1. Raise vehicle so both rear wheels can be rotated freely by hand. With one wheel stationary, rotate other wheel about 1/2 turn every second. Wheel should rotate freely. If both wheels turn, or try to turn, differential is defective.
2. Raise vehicle and have assistant in vehicle start engine. Allow it to idle at 600-800 RPM. If equipped with A/T, place transmission in Drive and apply brakes. If equipped with M/T, depress clutch and place transmission in first gear. Pull on one parking brake cable from under vehicle to lock one rear wheel.
3. With engine idling, on A/T models, slowly release brake. On M/T models, slowly release clutch. Locked rear wheel should remain stationary and free wheel should rotate slowly. As free wheel speed increases, differential should lock, causing both wheels to rotate or stop. If equipped with M/T, engine may stall.
4. It may be necessary to accelerate to 10 MPH to lock differential. If speed increases beyond 20 MPH without locking differential, unit is defective. Lock opposite wheel and repeat test.

REMOVAL & INSTALLATION

Same procedure is used to remove and install locking differential as conventional differential. See appropriate DRIVE AXLE article in this section.

1. On 9 1/2" ring gears, remove stop pin. On all models, use Governor Remover (J-26252) and remove governor bushing. Remove "C" clips which hold latching bracket in position on bracket shaft. Move bracket down shaft.
2. Using same tool, remove latching bracket bushing. Remove latching bracket, shaft and spring from case. Remove governor assembly from case. Remove lock screw, pinion shaft, differential pinion gears and pinion thrust washers. Rotate one side gear and roll gears out of case.
3. Remove thrust block, right side gear, right disc pack and side thrust washer. Remove left side gear, cam plate and disc pack as a unit. Remove thrust washer.

Cam Unit (7 1/2", 7 5/8" & 8 1/2" Ring Gear)

Remove snap ring, clutch plates, guide clips and wave spring. Remove cam plate and cam side gear.

Cam Unit (9 1/2" Ring Gear)

Measure and record overall length of gear assembly from front of gear to back of thrust sleeve, including side gear washer. Using Bearing Remover (J-22912-01), remove thrust sleeve. Press sleeve from side gear. Remove lock plates, guide clips, wave spring, cam plate and cam side gear.

INSPECTION

Clean all parts in solvent. Inspect all bearings, gear teeth and clutch plates and discs for signs of wear or overheating. If reaction block or flange shims must be replaced, replace with components of identical size.

REASSEMBLY & ADJUSTMENTS

If cam gear, right side gear or thrust block have to be replaced, differential must be adjusted. Selective thickness thrust washers behind each side gear, and a selective thickness thrust block between the side gears provide adjustment. The 3 adjustments to be made are

1. Left side gear backlash.
2. Right side gear backlash.
3. Thrust block clearance.

Left Side Gear Backlash

1. Install cam unit and thrust washer to flange end of case. Install pinion gears and thrust washer into differential. Ensure they are aligned with pinion shaft hole. Press down at side gear and install pinion shaft and lock screw. If side gear cannot be pressed down enough to install pinion shaft, replace thrust washer with one that is thinner.
2. Rotate pinion gear closest to lock screw so one tooth is pointing down. Insert a screwdriver firmly between side gear and pinion shaft. Install a dial indicator to ring gear flange. Position stem of dial indicator on one tooth of pinion gear closest to lock screw.
3. Pull pinion gear into its seat. Rotate gear and record reading. Repeat step for opposite gear. Backlash should be .010-.018" (.254-.457 mm). Use thrust washers to correct.

Right Side Gear Backlash

1. Alternately assemble lock plates. Use grease to hold clips in place. Install thrust washer, lock plate assembly and right side gear to differential. Install pinion gears and thrust washers. Ensure they are aligned with pinion shaft hole.
2. Press down side gear and install pinion shaft and lock screw. If side gear cannot be pressed down enough, replace thrust washer. Rotate pinion gear closest to lock screw so one tooth is pointing down.
3. Insert a screwdriver between side gear and pinion shaft. Follow procedure under «LEFT SIDE GEAR BACKLASH»(/gmc/cab-chassis-r3500/1985-1993/remont/differentials-drive-axles/#differential-locking__left-side-gear-backlash) to determine gear backlash. Backlash should be .002-.010" (.051-.254 mm). Use thrust washers to correct.

Thrust Block Clearance

1. Install left thrust washer, cam unit, right thrust washer and lock plates. Install right side gear, pinion shaft and lock screw. Insert a screwdriver firmly between each side gear and pinion shaft. Install a 1-2" telescoping gauge between side gear faces, not gear teeth. Measure side gear spread.
2. Remove telescoping gauge and measure with a micrometer. Measure original thrust block at outer corner with a micrometer. If thrust block thickness is not 0-.006" (0-.15 mm) less than side gear spread, adjust clearance.
3. Select a new thrust block the correct size to obtain correct clearance. Reshim right clutch disc pack. Backlash must remain .002-.010" (.051-.243 mm).

1. Install cam plate to cam side gear. Install wave spring. Install clutch plates. Ensure clutch plates are alternated upon installation. Install and press thrust sleeve until flush with side gear disc splines.
2. Install guide clips to plates, using grease to hold in place. If side gear or thrust sleeve were replaced, measure and record overall length of gear assembly from front of gear to back of thrust sleeve. Include side gear washer during measurement.
3. Compare measurement with that taken during disassembly. If new reading is more than .003" (.07 mm) greater or less than original, new thrust washer must be installed.

Install cam plate to cam side gear. Install wave spring. Install 8 clutch plates for 7 1/2-7 5/8" units and 10 clutch plates for 8 1/2" units. Ensure plates are alternated upon installation. (Scheme 15) Install snap ring. Install guide clips to plates, using grease to hold in place.

Scheme 15

1. Place axle shaft in vise in vertical position. Mount differential case over end of axle shaft, engaging spline of side gear with shaft. Grease 2 pinion gear thrust washers, and install left washer in its proper position. Install cam unit and right thrust washer.
2. Assemble 2 splined discs and 3 eared discs alternately onto bell end gear hub. Begin and end with eared disc. Install clutch pack guide clips on ears of bell end clutch pack.
3. Install right pinion gear through opening in case. Install thrust block, thrust washers and pinion gear. Install pinion gears 180 degrees apart. Rotate gears and thrust block into position. Ensure open side of thrust block faces small window opening.
4. Install pinion shaft and lock screw. Place governor assembly and latching bracket into case. Place straight end of latching bracket spring over and to outside of engagement shaft to preload latching bracket against governor assembly. Latching bracket bushing has tapered hole. Governor assembly bushing has straight hole.
5. Press governor bushing in case, making sure shaft end play is .004-.020" (.10-.51 mm). Press latching bracket bushing into case so end play is removed. Press stop pin flush with case. Install ring gear and side bearings on differential.

Differential & Cam Gear

1. With differential removed from housing, remove ring gear and side bearings. Remove 3 screws from front face of ring gear flange. Place differential on right side case half.
2. Using a screwdriver, gently pry case halves apart at yoke hole locations. Remove left side case half. Hold thumb against inside of gear hub when separating case halves. This will prevent side gear from falling out.
3. Remove governor assembly, latching bracket assembly, left side gear, left side clutch pack and guide clips. Remove left thrust washer, reaction blocks, pinion yoke, pinion gears and pinion thrust washers.
4. Remove right cam unit. Remove thrust washer and measure and record length of gear assembly from front of gear to back of thrust sleeve, including side gear thrust washer. (Scheme 17)
5. Using Rear Pinion Bearing Cone Remover (J 22912-01), press sleeve from side gear. Remove clutch plates, guide clips, wave spring, cam plate and cam side gear.

Clean all components in solvent. Inspect all bearings and gear teeth for excessive wear or damage. Inspect clutch plates and discs for overheating. If reaction blocks or flanges must be replaced, measure thickness of original components and replace with components of same size.

If cam gear, right side gear or thrust block have to be replaced, differential must be adjusted. Selective thickness thrust washers behind each side gear, and a selective thickness thrust block between the side gears provide adjustment. The 3 adjustments to be made are

1. Left side gear backlash.
2. Right side gear backlash.
3. Thrust block clearance.

Cam Unit

1. Install cam plate to cam side gear. Install wave spring and clutch plates. Ensure clutch plates are installed in correct order. (Scheme 16) Install thrust sleeve and press flush with side gear disc spline. Install guide clips to plates. Use grease to hold clips in place.
2. If side gear or thrust sleeve were replaced, measure and record overall length of gear to back of thrust sleeve. Include side gear thrust washer during measurement and compare with measurement obtained earlier. If new measurement is.003" (.07 mm) greater or less than original, new thrust washer must be installed.

Scheme 16

1. Install cam unit and thrust washer to right case half. Clamp cam unit in place using a set of washers, nut and bolt long enough to hold cam unit in place. Install pinion gears and thrust washers on pinion yoke. Install yoke firmly to differential case half. Loosen nut and position one pinion gear tooth down. Tighten nut.
2. Mount a dial indicator with a magnetic base on case half. Place stem of dial indicator on pinion gear tooth. Pull pinion gear firmly into its seat, and move gear back and forth. Note and record reading. DO NOT unseat pinion yoke as this will make reading inaccurate. Repeat step for other 2 pinions.
3. Backlash should be between .010-.018" (.254-.457 mm). If backlash is too high, use a thicker thrust washer. If backlash is too low, use a thinner thrust washer.

1. Assemble lock plates alternately. Install guide clips to plates, using grease to hold in place. Install thrust washer, lock plate assembly and left side gear to differential. Clamp side gear in place using washers, nut, and a bolt long enough to hold side gear in place.
2. Place pinion gears and thrust washers on pinion yoke. Install yoke firmly to differential case half. Loosen nut, and position one pinion gear tooth down. Tighten nut.
3. Install a magnetic base dial indicator on case half. Position stem of dial indicator on pinion gear tooth. Pull pinion gear firmly into its seat. Rotate gear back and forth while recording reading. DO NOT unseat pinion yoke as backlash reading will be inaccurate. Repeat procedure for other 2 pinions.
4. Backlash should be between .002-.010" (.051-.254 mm). If backlash is too high, install a thicker thrust washer. If backlash is too low, install a thinner thrust washer.

Reaction Block

1. Install left thrust washer, right thrust washer, side gear and cam assembly. Measure distance from side gear face to case half face. Thickness of straightedge must be subtracted from this measurement. Add measurement of both sides together. This is side gear spread. Measure thickness of original reaction blocks together.
2. If reaction block thickness is not 0-.006" (0-.15 mm) less than side gear spread, adjust clearance by using reaction blocks of the correct thickness or reshimming left clutch pack. Backlash must remain .002-.010" (.051-.254 mm).

Scheme 17

1. Install right thrust washer and right cam unit. Install reaction blocks, pinion yoke, pinion gears and pinion thrust washers. Install left thrust washer. Insure plates are assembled in proper order. Install left side gear and latching bracket assembly.
2. Install governor assembly. Ensure straight end of latching bracket spring is over and outside governor assembly shaft. Hold side gear in left side case and install case halfs together. Install screws, ring gear and differential side bearings.

See also:
• DRIVE AXLE RATIO IDENTIFICATION
• LEFT SIDE GEAR BACKLASH