Drive Axle - 7.5", 8.5" & 9.5" GMC Cab & Chassis R2500

IDENTIFICATION

General Motors uses several types of specific axles. The 7-1/2", 8-1/2" and 9-1/2" axles can be distinguished from others by the configuration of their housing covers and by the number of the attaching bolts. To determine the drive axle ratio, refer to the DRIVE AXLE RATIO IDENTIFICATION article in this section.

Scheme 4

AXLE SHAFTS & BEARINGS

Note. For front axle shaft and bearing removal, see articles on SPICER (DANA) FULL-FLOATING AXLES or 4WD STEERING KNUCKLES in this section.

Scheme 5

Scheme 6

1. Raise vehicle. Remove wheel and brake drums. Drain lubricant from drive axle. Remove housing cover. Remove differential pinion shaft lock bolt.
2. Remove differential pinion shaft. Push flanged end of axle shaft toward center of vehicle. Remove "C" lock from button end of axle shaft.
3. Remove axle shaft from axle housing, being careful not to damage seal. Rotate differential case until pinion shaft touches edge of housing. (Scheme 5)
4. Reach into case with screwdriver and rotate "C" lock until its open end points directly inward. When "C" lock is correctly positioned, axle shaft can be pushed inward, allowing "C" lock to be removed. Remove axle shaft. (Scheme 6) CAUTION: DO NOT hammer on axle shaft. It should slide easily when "C" lock is correctly positioned. When removing axle shaft on the 9 1/2" ring gear axle, be sure thrust washer in differential case does not slip out.
5. With axle shaft removed, insert Bearing Remover (J-22813-01 for 7 1/2", J-23689 for 8 1/2", J-29712 for 9 1/2" ring gear) into axle housing behind bearing. Attach Slide Hammer (J-2619) and Adapter (J-2619-4) for 7 1/2" ring gear, Slide Hammer with Adapter (J-2619-01) for 8 1/2" and 9 1/2" ring gear, to bearing remover and remove axle bearing and axle seal.

Installation (Semi-Floating)

1. To install, reverse removal procedure. Using Bearing Installer (J-34974 for 7 1/2", J-23690 for 8 1/2" and 9 1/2" ring gear), install axle shaft housing bearing until bearing installer bottoms against housing shoulder.
2. Using Seal Installer (J-33782 for 7 1/2", J-21128 for 8 1/2" and 9 1/2" ring gear), install axle shaft housing seal until flush with outer edge of axle tube. After installing axle shaft and "C" lock, pull axle shaft outward so "C" lock seats in side gear counterbore. (Scheme 6)

Removal (Full-Floating)

1. Remove bolts attaching axle shaft flange to wheel hub. Tap on flange with soft-faced hammer to loosen shaft.
2. Grip rib on end of flange with locking pliers and twist to start shaft removal. Remove shaft from axle tube. Thoroughly clean axle shaft flange and end of wheel hub.

Installation (Full-Floating)

1. Use a new gasket or apply silicone sealant over axle shaft. Position axle shaft in housing so shaft splines enter differential side gear.
2. Position axle shaft so holes align and install flange-to-hub attaching bolts. Tighten bolts.

Removal

1. Raise vehicle and allow axle to hang free. Disconnect universal joint and tie drive shaft out of the way.
2. Rotate pinion shaft through several revolutions, using an INCH lb. torque wrench. Note and record pinion bearing preload. Mark relationship of pinion flange and shaft for reassembly. Count number of threads on pinion shaft.
3. Hold flange with Companion Flange Holder (J-8614-01) and remove self-locking nut. Using Pinion Flange Remover (J-8614-1, J-8614-2 and J-8614-3 for 7 1/2" and J-8614-01 for 8 1/2" and 9 1/2" ring gear), remove pinion flange. Pry pinion seal from housing.

Note. Be careful, not to damage differential carrier when removing pinion seal.

Installation

1. Inspect pinion flange oil seal surface, drive splines, ears and bearing contact surface. Replace pinion flange (if necessary). Pack seal lip cavity with lithium base extreme pressure lubricant. Place pinion seal in bore.
2. Using Seal Installer (J-23911 for 7 1/2" ring gear), Gauge Plate (J-22804-1 for 8 1/2" and 9 1/2" ring gear) and Seal Installer (J-22836 for 8 1/2" and J-22388 for 9 1/2" ring gear), drive pinion seal into place.
3. Make sure seal is square in carrier. Pack cavity between end of pinion splines and pinion flange with a non-hardening sealer. Using Companion Flange Holder (J-8614-01), install flange on pinion shaft.
4. Install washer and nut in original position, taking note of scribe marks and number of exposed threads. Measure pinion preload. Tighten nut in small increments, until preload exceeds original figure by 3-5 INCH lbs. (.3-.6 N.m). Install drive shaft and lower vehicle.

Note. DO NOT hammer flange onto pinion shaft, as ring gear and pinion will be damaged.

1. Raise vehicle. Drain lubricant. Remove rear wheels and brake drums. Remove parking brake cable. Disconnect drive shaft and brake lines. Disconnect vent hose from vent fitting at axle housing. Disconnect shock absorbers at lower brackets.
2. Disconnect height sensing and brake proportional valve linkage (if equipped). Remove stabilizer shaft (if equipped). Remove "U" bolt nuts, washers, spacers and spring plates from axle assembly. Lower axle assembly and remove from vehicle.

To install axle assembly, reverse removal procedure. Bleed brake system.

DESCRIPTION

Note. General Motors 8 1/2" ring gear drive axle is used as the front drive axle on K10/20 models. For removal and installation instructions, see articles on LOCKING HUBS and 4-WHEEL DRIVE STEERING KNUCKLES. These models may also be equipped with a Dana (Spicer) front drive axle. See appropriate article in this section.

Axle assembly is hypoid gear type with integral carrier housing. It is used on Light Duty emission vehicles with semi-floating and full-floating axles. Pinion bearing preload is made with a collapsible spacer. Differential side bearing preload adjustment and drive pinion depth adjustment are made by shims. A removable housing cover permits inspection and minor servicing of differential without removing axle from vehicle. Service procedures are the same for all assemblies, except for TORQUE SPECIFICATIONS and special tool numbers.

DISASSEMBLY

Note. Check and record ring gear backlash and pinion bearing preload before disassembly.

1. Remove lock screws retaining pinion shaft and remove pinion shaft. Remove axle shafts, and roll out differential pinions and thrust washers. Mark pinions and thrust washers for reassembly. Remove side gears and thrust washers. Mark side gears and thrust washers for reassembly.
2. Mark differential bearing caps and housing for reassembly. Loosen bearing cap bolts, and tap bearing cap surfaces to loosen caps. Using pry bar inserted in differential carrier, pry against housing at differential window to remove carrier. NOTE: Be careful, as carrier bearings are preloaded. Carrier will fall free after being pried past a certain point.
3. After removing carrier, place shims with appropriate bearing cups. Install bearing caps onto housing in their original position before removal. Using Differential Side Bearing Remover (J-22888 and J-8107-2 for 7 1/2" ring gears, J-8107-4 for 8 1/2" and J-8107-3 for 9 1/2" ring gear), remove differential side bearings. NOTE: Ring gear bolts on 7 1/2" axles have left-hand threads.
4. Remove ring gear bolts. Tap ring gear off carrier using a soft drift and hammer. Using an INCH lb. torque wrench, check torque required to rotate drive pinion. If no preload reading is obtained, check for looseness of pinion assembly. Looseness indicates pinion bearings should be replaced.
5. Install Companion Flange Holder (J-8614-11) on flange with holder notches toward flange. Remove pinion nut and washer, and remove flange. Install pinion nut halfway on pinion. Install differential cover using 2 bolts. Tap end of pinion, using soft drift and large hammer to remove pinion. NOTE: DO NOT damage pinion bearings when removing pinion from differential housing.
6. Remove differential cover and pinion assembly. Remove pinion oil seal and front bearing from housing. Remove collapsible spacer from pinion. Remove inner bearing and shim from pinion. Using Bearing Remover (J-25320), press bearing from pinion.
7. Remove bearing cups from axle housing using hammer and punch using slots for this purpose. Inspect bearings and bearing cups, and replace them as required. Discard oil seal, pinion nut and collapsible spacer.

CLEANING & INSPECTION

Clean all parts in cleaning solvent. Inspect all bearings, bearing cups, races and rollers for chipping or excessive wear. Inspect axle shaft, ring gear and pinion for scoring, cracking or chipping. Inspect differential case, pinion side gears, thrust washers and pinion shaft for cracks or excessive wear.

Case Assembly

Using guide pins (if necessary), install ring gear squarely onto case. Tighten ring gear bolts evenly and alternately. Install side gears, differential pinions and thrust washers into case. Install differential pinion shaft and lock screw. Tighten lock screw finger tight.

Scheme 7

Scheme 8

1. Drive pinion rear bearing shim thickness must be determined whenever a new axle housing, ring and pinion set, or pinion bearings are installed. Shim pack thickness is determined by using Pinion Setting Gauge Set (J-21777).
2. If removed, install pinion bearing cups into housing. Place lubricated pinion bearings into cups. Position Gauging Plate (J-23597-11 for 7 1/2", J-21777-29 for 8 1/2" and J-21777-85 for 9 1/2" ring gear) and rear pinion bearing pilot on preloaded stud.
3. Install through rear pinion bearing, front pinion bearings and Bearing Disc (J-21777-42). Tighten hex nut until snug. Rotate bearings to insure proper seating. Hold preload stud stationary with a wrench on flats. Tighten hex nut until 20 INCH lbs. (2.2 N.m) are required to rotate bearings. (Scheme 7)
4. Mount Side Bearing Gauging Discs (J-21777-45 for 7 1/2" and 8 1/2" and J-21777-86 for 9 1/2" ring gear) on ends of arbor. Place arbor into carrier making sure discs are properly seated. Install side bearing caps and bolts. Tighten bolts to avoid movement.
5. Position dial indicator on mounting post of arbor, with contact button resting on top surface of plunger. Set dial indicator at zero. Push indicator down on indicator shaft until needle rotates 3/4 revolution to the right, then tighten in this position.
6. Preload dial indicator 1/2 revolution, then tighten in this position. Place plunger onto gauging area of gauge plate. Rock plunger rod slowly back and forth across gauging area until dial indicator reads greatest deflection.
7. Set indicator to zero. Repeat rocking action several times to verify setting. Once zero reading is obtained, swing plunger until it is removed from gauging area.
8. Dial indicator will now read required pinion shim thickness for a "nominal pinion". Record this reading. Check drive pinion for painted or stamped markings on pinion stems, or for a stamped code number on small end of pinion gear.
9. If marking is found to be plus or minus number (for example, +2 or -5) add or subtract that many thousandths of an inch from indicator reading. This will then be the required thickness of rear pinion bearing shim pack. NOTE: If no markings are found on pinion, use dial indicator reading as shim thickness.
10. Remove bearing caps and gauging tool from housing. Place selected shim pack on pinion gear. Using a press, install lubricated pinion bearing onto pinion shaft.
11. Install a new collapsible spacer over pinion gear shaft. Position pinion assembly in housing. While holding pinion forward, carefully drive front pinion bearing onto pinion gear shaft until a few threads are exposed.
12. Install seal, pinion flange, washer and nut. Tighten nut until all end play is removed. Rotate pinion several times to seat bearings. Check preload using an INCH lb. torque wrench.
13. Continue tightening nut, and checking preload until specified preload is obtained. DO NOT back off nut to lessen preload.
14. If preload is exceeded, a new collapsible spacer must be installed, and nut must be retightened until proper preload is obtained.

Side Bearing Preload

1. Lubricate bearings, and place differential assembly into position in housing. Hold in place by hand.
2. Install Bearing Strap (J-22779-6) on left bearing. Tighten bolts evenly to a snug fit. Install right bearing cap. Tighten bolts to a snug fit.
3. Position ring gear tight against pinion, so backlash is .000-.001" (0-.025 mm). Insert Gauge Tool (J-22779) between left bearing cup and carrier housing.
4. While moving tool up and down, tighten adjusting nut until a slight drag is felt. Tighten lock bolt on side of tool.
5. Install adjustment spacer and shim between right bearing cup and axle housing. Insert a feeler gauge, thick enough to create a slight drag, between shim and carrier.
6. Remove bearing strap, backlash gauge, spacer, shim, feeler gauge and differential case from axle housing. Using a micrometer, measure and average readings in 3 places. Add together dimensions of shim, spacer and feeler gauge. Record measurement.
7. Subtract .010" (.25 mm) from ring gear (left) side measurement and add .010" (.25 mm) to opposite (right) side measurement. This allows for correct backlash adjustment.
8. To obtain correct preload, add .004" (10 mm) to both measurements. The total is the correct shim pack thickness for each side. See following example: Ring Gear Side (Left) Shim Pack .250" (Gauging Tool Measurement) -.010" (Backlash Adjustment) +.004" (Bearing Preload) =.244" (Ring Gear Side Shim Pack) Opposite Ring Gear Side (Right) Shim Pack .265" (Combined Measurement Total) +.010" (Backlash Adjustment) +.004" (Bearing Preload) =.279" (Opposite Ring Gear Side Shim Pack)
9. Install ring gear side shim first. Wedge opposite side shim between bearing cup and spacer. Install shim so chamfered side is against spacer. NOTE: If shim is not chamfered enough and scrapes spacer when it is installed, file or grind chamfer before installation.
10. It may be necessary to partially remove differential when right side shim is installed. Tap shim into place with a soft-faced hammer. Tighten bearing cap bolts to specifications.

Backlash & Final Assembly

1. Check backlash at 4 locations around ring gear, using a dial indicator mounted to axle housing. Variation should not exceed .001" (.025 mm). If backlash is incorrect, adjust side bearing shims as necessary. CAUTION: Total shim pack thickness must not be changed. If a shim is removed from one side, the same thickness shim must be added to the other side.
2. After adjustment is completed, make a tooth contact pattern test, and make any necessary corrections. Install axle shafts and housing cover.

ASSEMBLY SPECIFICATIONS

AXLE ASSEMBLY SPECIFICATIONS

TORQUE SPECIFICATIONS

TORQUE SPECIFICATIONS

See also:
• DRIVE AXLE RATIO IDENTIFICATION