NEW PROCEDURE FOR REPLACEMENT OF FINAL DRIVE PINION

Model and Year: 1980-89 A, J, L, X WITH 125C OR 440-T4 TRANSAXLE

TO: ALL CHEVROLET DEALERS

This bulletin covers a new service procedure to replace Final Drive Pinion Gear Washers (807) and differential carrier sun gear bearing (677) on THM 440-T4/HYDRA-MATIC 4T60 or (676) on THM 125C/HYDRA-MATIC 3T40.

SERVICE PROCEDURE:

Checking End Play -

Measure pinion gear end play using a feeler gage. The correct end play range is 0.24 - 0.63mm (0.009" - 0.025"). If out of range, follow the procedure given in this bulletin, since it is not currently included in the Unit Repair section of your Service Manual. Refer to illustration.

Disassembly -

1. After removing final drive from unit, clean the entire bottom pan since it will be used to hold needle bearings.

2. Using a screwdriver, remove the spiral snap ring (wear safety glasses). (Figure 1)

3. Be careful when pulling out the pinion gear shaft (804) from pinion gear so needle bearings do not get lost. (Figure 2) Put a mark on the gear with chalk or crayon so the gear can be installed the same way it was removed. Overhaul one pinion at a time so parts do not get mixed.

4. Tilt final drive and remove the pinion gear (808). Washers (806, 807, 809) and needle bearings. (Needle bearing will fall out of pinion gear. Use bottom pan to catch/hold them.) (Figure 3)

5. Inspect washers, needle bearings and pinion shaft for wear. Discard bronze washer (806) and replace with new steel washer (807) from service kit.

* If replacement of only the thrust bearing (Figure 2) (677) 4T60 or (676) 3T40 is necessary, use Steps 1 through 3. After Steps 1 through 3 are completed move pinion gears to provide clearance to replace thrust bearing, then complete Steps 6 through 7 of assembly procedure.

Assembly -

1. After cleaning pinion gear, apply Transjel J36850 (assembly lubricant or petroleum jelly) to the inside of gear. (Do not use any grease or axle grease.)

2. Install square cut washer (809) onto pinion gear shaft (804). Insert the shaft and washer into gear so washer is flush with gear and shaft is 3/4 inside gear.

Important: Square cut washer is to be assembled between the two rows of needle bearings.

3. Install needle bearings (805) (one at a time) into gear - 44 per pinion (22/row) for 3.06 and 3.33 ratios - 36 per pinion (18/row) for 2.84 ratio. Occasionally twist pinion shaft, so needle bearings will line up and allow for all needle bearings to be installed. (Figure 5)

4. Install 2 washers (807) into final drive assembly. (Figure 6)

5. Install remaining 2 washers (807) (on top of pinion gear). (Figure 6)

6. Insert pinion gear and washers (in same position it was removed) into final drive. Check chalk or crayon mark.

Important: Make sure the pinion gear is installed the same way that it was removed. If the gear is installed upside down, it may cause a noise because of the change in set wear pattern.

7. Install pinion gear shaft (804) (without dislodging needle bearings) and install spiral snap ring. (Figure 6)

IMPORTANT: Make sure there are no extra needle bearings left after replacing washers. There must be no spaces between needle bearings. Check for pinion end play.

Do not install more than the required amount of washers (4) per each pinion (2 on each side of pinion) into the final drive.

LABOR TIME INFORMATION:

Add .4 hours to Labor Operation K7620 whenever this service procedure is performed.

SERVICE PARTS INFORMATION:

Whenever ordering replacement parts for the final drive assembly refer to the following part numbers:

Package Description Part Numbers ------------------- ------------ 1. Package: Pinion, Thrust Washers for 2.84 ratio 8637994 final drive - 16 steel washers (807)

2. Package: Pinion, Thrust Washers for 3.06 and 3.33 8637995 ratio final drives - 16 steel washers (807)

3. Bearing, differential sun gear 8646254

Parts are currently available from GMSPO.

SERVICE MANUAL REFERENCE:

Whenever service and/or replacement to the Final Drive Assembly is necessary refer to the Unit Repair section of your Service Manual.

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.