Steering - Procedure Identifying Torque Steer
88pontiac23Bulletin Number: 88-3-25A
Reference Number: 833103R
Publish Date: 10/88
Subject: "TORQUE STEER" - PROCEDURE IDENTIFYING TORQUE STEER
Models
Affected: 1980-88 6000, BONNEVILLE, SUNBIRD, GRAND AM, AND GRAND PRIX FRONT WHEEL DRIVE VEHICLES
"This bulletin replaces bulletin 88-3-25, dated 6/88. This bulletin has been revised to include the manual transmission in Step 3 under the "TORQUE STEER" Diagnosis Chart and possible causes. Also revised illustrations showing the manual transaxle."
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 the appropriate service manual.
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.
WARRANTY INFORMATION
Labor Operation: T1347
Labor Time : NOTICE: THIS IS A S.T. (STRAIGHT TIME) OPERATION
WHICH REQUIRES TIME DOCUMENTATION AS DETAILED IN THE POLICIES AND PROCEDURES MANUAL. ZONE APPROVAL IS REQUIRED BEYOND .5 HOURS.
"TORQUE STEER" DIAGNOSIS