NEW DRIVEN SPROCKET SUPPORT AND CHAIN SCAVENGING SCOOP

MODELS AFFECTED: 1990 DE VILLES, FLEETWOODS, ELDORADOS, SEVILLES, AND ALLANTES

1. New Driven Sprocket Support and Chain Scavenging Scoop - THM 440-T4 (HYDRA-MATIC 4T60).

A new driven sprocket support and chain scavenging scoop was introduced into production on August 16, 1989 (Julian Date 228). Refer to Figure 1. The change to the driven sprocket support required the chain scavenging scoop to be shortened to 1/3 of its previous length.

Service Notes:

The new driven sprocket support can be used to service past models but the chain scavenging scoop must be shortened to fit. Refer to Figure 2. Smooth the cut surface. SERVICE PARTS INFORMATION ------------------------- P/N Description Model Year --- ----------- ---------- 8668385 Support Assembly, Driven Sprocket 1985-1990

8668613 Scoop, Chain Scavenging 1985-1990

35 tooth driven sprocket natural color must be used with new support only*

8651622 Scoop, Chain Scavenging 1985-1990

33 tooth driven sprocket black color must be used with new support only*

2. New Parking Lock System - THM 440-T4 (HYDRA-MATIC 4T60).

A new parking lock system was introduced into production on September 25, 1989 (Julian Date 268). This included changes to the following parts:

Actuator guide. Refer to Figure 3. Parking lock actuator assembly bullet. Refer to Figure 4. Transaxle case bore. Refer to Figure 5. Parking pawl including elimination of the lock-out pin. Refer to Figure 6.

Service Notes:

The new parking lock system will not service past models unless ALL the components are replaced including the transaxle case. The new system will assemble the same way as the previous system.

SERVICE PARTS INFORMATION

P/N Description Model Year ---- ----------- ---------- 8668985 Case, Transaxle (Common) 1990 8675325 Guide and Seal Assembly 1990 8675335 Actuator Assembly, Parking Lock 1990 8675330 Gear Assembly, Final Drive Internal 1990

3. New Wiring Harnesses and Pressure Switches - THM 440-T4 (HYDRA-MATIC 4T60) and THM F-7

New second, third, and fourth clutch circuit pressure switches and wire harness connectors were implemented into production on September 6, 1989 (Julian Date 249). The switches and wires will have "button headed" connectors instead of the previous blade design. Refer to Figures 7 and 8.

SERVICE PARTS INFORMATION - ------------------------- P/N Description Model Year --- ----------- ---------- 12096127 Harness Assembly, Wiring, THM 440 1990 12096322 Harness Assembly, Wiring, THM F-7 1990 8668271 Clip, Wire Conduit 1990 8668707 Switch Assembly - Pressure 1990 (Fourth Clutch) (N.C.) 8668707 Switch Assembly - Pressure 1990 (Third Clutch) (N.C.) 8668709 Switch Assembly - Pressure, THM F-7 1989-1990 Discrete (Second Clutch) (N.C.)

4. Two Plate Fourth Clutch Assembly - THM 440-T4 (HYDRA-MATIC 4T60)

Starting at SOP, a new two plate fourth clutch assembly (501) and apply plate (502) was used to replace the single plate fourth clutch assembly. The extra plate was added for the higher engine torque requirements. Component changes (Figure 9) included:

Fourth clutch plates are thinner at the steel part; the fiber material was not changed. The two plate assembly has four white stripes; the one plate assembly has four green stripes.

Fourth clutch reaction plates are thinner by 0.1 mm.

Fourth clutch apply plate does not have the step used on the single apply plate, but does have a slight machined-in taper.

Service Notes:

When servicing a 1990 transaxle, rebuild or replace the fourth clutch components with the same type (single or two plate). Refer to Figure 10. See Service Parts Information for appropriate part numbers.

IMPORTANT: Do not install two plate components or the entire two plate fourth clutch assembly into a single plate transaxle or vice-versa. Fourth clutch apply calibrations and durability will be affected.

SERVICE PARTS INFORMATION

P/N Description Model Year --- ----------- ---------- 18017246 Plate Assembly - Fourth Clutch 1990 (fiber for two plate type) 8661004 Plate Assembly - Fourth Clutch Apply 1990 (two plate type) 8661006 Plate Assembly - Fourth Clutch Reaction 1990 (steel for two plate type) 8662986 Package - Overhaul Repair Complete 1990

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.