NO FOURTH GEAR/THM325-4L DIAG.PROCEDURE/CODE 29,39

Some 1982 and 1983 THM 325-4L transmissions may experience a no fourth gear condition. The following diagnosis procedure will aid in determining the cause for this condition.

DIAGNOSIS PROCEDURE

Test drive the vehicle applying a light throttle in drive range to about 30-35 m.p.h. (Third gear). Move the selector lever into manual second and release the throttle. The transmission should downshift and coastdown overrun braking should occur.

1. If coastdown overrun braking does occur, refer to the diagnosis procedure for no fourth gear in your Service Manual.

2. If coastdown overrun braking does not occur, remove the transmission from the vehicle. Inspect the overrun clutch housing for a break in the hub weld. If the hub weld is broken, the cause is due to misaligned pinions in the overdrive carrier.

In all instances where the hub weld is broken on the overrun clutch hosing, both the overrun clutch housing (Part Number 8635941 Figure 1) and the overdrive carrier (Part Number 8635036 Figure 2), must be replaced.

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.