SERVICE MANUAL UPDATE SEC. 7B MANUAL TRANSAXLE REPAIR

Subject: MANUAL TRANSAXLE UNIT REPAIR

Model and Year: 1990-91 GEO STORM

TO: ALL CHEVROLET DEALERS

This bulletin is an addition to the procedures located in ISUZU 76 mm Manual Transaxle Unit Repair (Section 7B2) of the 1990 GEO Storm Service Manual (ST371-90) and the 1991 GEO Storm Service Manual (ST371-91). Because this transaxle is unique in its use of pins to control shift shaft operation, this bulletin has been written to describe the different types of pins, their locations and their function.

TRANSAXLE PINS

LOCK PINS

There are two lock pins in this transaxle; one is 12 mm long and the other is 13 mm long. The 12 mm lock pin is located in the bottom of the 5th shift shaft where it joins the lower transaxle case. The 13 mm lock pin is located in the bottom of the 3rd/4th shift shaft at the lower transaxle case (Figures 1 and 2). These lock pins are used in conjunction with three 10 mm interlock pins to prevent the transaxle from being shifted into two or more gears at one time.

10 mm INTERLOCK PINS

This transaxle also uses four interlock pins that are 10 mm long. Three are used in conjunction with the lock pins in the lower transaxle case (Figure 1). A fourth pin is located in the reverse/5th shift block (Figure 2). It prevents the transaxle from being shifted from fifth gear to reverse without going through neutral.

ROLL PINS

The roll pins are used to hold shift forks, shift blocks, etc. to the shift shafts and the shift lever. These pins are rolled steel and may not be reused. After they are removed, they must be discarded.

Always use new roll pins during reassembly.

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.