TORQUE STEER -FRT. WHEEL DRIVE DIAGNOSTIC AIDS & PROCEDURE

Model and Year: 1980-88 CHEVROLET FRONT WHEEL DRIVE VEHICLES

TO: ALL CHEVROLET DEALERS

Chevrolet Dealer Service Bulletin 88-260-3B dated June, 1988, is being revised to include manual transaxle equipped vehicles. All copies of 88-260-3B should be discarded.

Some vehicles may exhibit a tendency to steer left or right while driving straight. This bulletin provides a procedure for identifying "Torque Steer" (left or right steer forces that result from applied engine torque).

DEFINITIONS

"TORQUE STEER": Under heavy acceleration from 40 mph on a smooth, flat road the vehicle has a left or right steering force that is eliminated when the transmission is placed in neutral. The magnitude of the steering force is normally dependent upon the amount of applied engine torque.

"LEAD": On a smooth, flat road with the transmission in neutral, the vehicle does not require a noticeable torque input to the steering wheel to maintain a straight direction; however, with hands removed from the steering wheel, the vehicle steers left or right.

"PULL": On a smooth, flat road with the transmission in neutral, the vehicle requires a noticeable torque input to the steering wheel to maintain a straight direction.

A road test will be necessary to determine if a "Lead/Pull" or "Torque Steer" condition exists. Prior to a road test, the following should be checked and corrected:

1. Tires should be the same size, make, and tread depth.

2. Adjust tire pressure to specification.

3. Inspect for loose, worn, damaged or incorrect suspension components.

Drive the vehicle on a straight, smooth, flat (crown free), road surface at 40 mph. Shift the transmission to neutral and allow the vehicle to coast. Momentarily release the steering wheel and note if there is a change in the direction of vehicle travel.

CAUTION:

THE DRIVER'S HANDS SHOULD NOT BE MOVED FROM THEIR STEERING POSITION DURING THE MOMENTARY RELEASE OF THE STEERING WHEEL.

A deviation from a straight direction indicates a "Lead/Pull" condition. If a "Lead/Pull" condition exists, follow the procedures outlined in Chevrolet Dealer service Bulletin 87-212-3 dated October, 1987.

If no change in steering direction occurs with the transmission in neutral, place the transmission in gear, and while proceeding at 40 mph, momentarily apply maximum acceleration (WOT - wide open throttle). If a change in steering direction is noted, the vehicle exhibits "Torque Steer".

NOTICE: IT IS IMPORTANT TO REPEAT EACH ROAD TEST WHILE TRAVELING IN THE OPPOSITE DIRECTION TO ELIMINATE FACTORS SUCH AS CROSSWIND.

In conjunction with the attached "Torque Steer" Diagnosis chart, the following possible causes of "Torque Steer" should be evaluated and repaired as necessary:

1. Slight difference in drive wheel tire diameter (cannot be measured). Vehicle will steer in direction of the smallest diameter tire.

2. Difference in left and right "Z" heights. Refer to service manual for "Z" height measurement procedure and specification. Vehicle must be resting on its wheels when "Z" height measurement is taken. When correcting "Z" height always match the lowest reading.

3. Difference in left and right drive axle angles.

Automatic Transmission - Differences in drive axle angles will be indicated by measuring a difference in the transmission left and right pan rail height. (See Illustration).

Manual Transmission - Differences in drive axle angles will be indicated by measuring a difference in the height of the axles as measured at the largest diameter of the inboard axle joint. (See Illustration).

4. Loose, worn, incorrect or damaged suspension components. Check items that could result in unequal drive wheel toe during acceleration.

Labor Operation Number: T1347

Labor Time: NOTICE: THIS IS A ST. (STRAIGHT TIME) OPERATION WHICH REQUIRES TIME DOCUMENTATION AS DETAILED IN THE CLAIMS PROCESSING MANUAL. BRANCH APPROVAL IS REQUIRED BEYOND .5 HOURS.

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.