SERVICE AND PARTS INFORMATION 125 FINAL DRIVE ASSEMBLY

MODELS AFFECTED: 1988 CENTURYS, SKYHAWKS, AND SKYLARKS ---------------- EQUIPPED WITH A THM 125C (MD9) TRANSAXLE

BULLETIN COVERS

New style Final Drive Assemblies (678) for some 1988 vehicles equipped with a THM 125C transaxle having 3.33, 3.06, 2.84 final drive ratios. These new final drive assemblies have larger differential side gears (687) and larger differential pinion gears and a smaller diameter cross shaft which is black in color. The new style Final Drive Assemblies are going into production due to the increased use of higher torque engine calibrations.

DATE OF PRODUCTION CHANGE (Refer to Figure 1)

May 3, 1988 (Julian Date 124) for all THM 125C transaxles using a 3.33 ratio final drive assembly. Future production changes are scheduled for May 23, 1988 (Julian Date 144) for all models using the 3.06 ratio final drive assembly and S.O.P. 1989 for some models using the new style 2.84 ratio final drive assembly.

SERVICE ACTION

When servicing a 1988 THM 125C transaxle use the parts listed in the Service Parts information section below. Do not attempt to mix new style ,final drive components with previous final drive components that look similar or the following conditions will occur:

o The final drive pinions (2) and final drive internal gear (673) will not mesh together due to new larger style final drive.

o All selective measurements taken will be inaccurate, resulting in a misbuild.

SERVICE PARTS INFORMATION (Refer to Figure 2)

The new style final drive can be identified by three physical characteristics:

1. The Differential Pinion Shaft (682) is smaller in diameter and black in color (normally silver).

2. The Differential Side Gears (687) have 16 teeth instead of 15 teeth.

3. The Differential Pinion Gears (685) have 10 teeth instead of 11 teeth.

When ordering parts to service THM 125C transaxles equipped with new style final drives, use the following part numbers listed below:

Part No Description ------- ----------- 8662922 Package, Final Drive (3.33 final drive ratio)

8661905 Package, Final Drive (3.06 final drive ratio)

8662923 Package, Final Drive (2.84 final drive ratio)

8662924 Package, Differential Side Gear

When ordering parts to service THM 125C transaxles with previous style final drives, use the following parts numbers listed below:

Part No Description ------- ----------- 8643963 Package, Final Drive (3.33 final drive ratio)

8643990 Package, Final Drive (3.06 final drive ratio)

8653941 Package, Final Drive (2.84 final drive ratio)

8646919 Package, Differential Side Gear

SERVICE MANUAL REFERENCE

Refer to the THM 125C (MD9) Automatic Transaxle Unit Repair section whenever servicing the Differential and Final Drive.

SERVICE NOTES

Use the chart below to identify transaxle models and the models and the final drive ratios they contain:

Production Final Drive Date Ratio Transaxle Model Code ---- ----- -------------------- May 3, 1988 3.33 CPC, HYC, HZC, JKC, JMC, JNC, JUC, JXC, RAC, RCC

MAY 23, 1988 3.06 HFC, HHC, HJC, HLC, HRC, HTC, KCC, JAC, JDC, JPC, JWC, TAC, TBC

S.O.P. 89 * 2.84 BBC, BUC, CBC, CHC, CJC, CMC, CRC, CTC, CUC, KDC, KKC, LUC, PDC, PJC, PMC, PNC, PPC, PRC, PSC, RTC, RUC, TNC, TRC

* In models equipped with 2.84 ratio final drives, both the new style final drive and current style final drives are used.

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.