Fiero L4-151 2.5L (1985)
Axle Shaft: Technical Service Bulletins
Drivetrain - Torque Steer Diagnosis
Number
85-3-21
Date
10/85
Subject:
TORQUE STEER
ALL FRONT-WHEEL DRIVE CARS
A degree of torque steer to the right may normally be experienced during heavy throttle application on some front-wheel-drive vehicles. This is due to
the right drive axle being longer than the left axle and associated difference in axle angle.
The axle difference results in more torque toe-in effect to the left front wheel, especially on manual transmission-equipped cars. This condition may be
noticed on Grand Ams when accelerated from a standing start and on some 6000 models at lower speeds. A simple measurement to determine the degree
of torque steer is to place a small piece of tape at the top center of the steering wheel. Drive the car and note the inches of steering wheel deflection
required to steer the car straight under heavy throttle acceleration. A comparison of like cars will then determine if a particular car has a greater than
normal degree of torque steer. The following factors may cause torque steer to be more apparent on a particular car:
1.
A slightly smaller diameter tire on the right front will increase a right torque lead. Inspect front tires for difference in brand, construction, or size.
If the tires appear similar, change the front tires side to side and retest the car. Tire and wheel assemblies have the most significant effect on
torque steer correction.
2.
Large difference in right and left front tire pressure.
3.
Any looseness in control arm inner bushings, steering linkage, or steering gear mounting which permits a front wheel to pull forward and toe-in
under torque more than the opposite side. A loose suspension component may also result in an opposite lead on deceleration.
4.
High front suspension height which would increase drive axle angle.
5.
Binding or tight drive axle joint. A tight joint or high-suspension height may also exhibit a wobble condition between 15 mph and 30 mph. This
condition is reduced with increased mileage.
6.
Incorrect, worn, or loose engine mounts causing adverse drive axle angles. The less prominent the left drive axle angle is the less the right torque
steer effect will be. However, shimming the engine mounts or cradle has not resulted in more than a minor improvement of torque steer.
The following conditions affect car steering pleasurability and/or a constant right or left lead independent of torque steer causes. However, the existence
of one or more of these conditions may compound a torque steer complaint:
1.
Incorrect front-wheel alignment or a rear-wheel alignment condition which would cause the car not to track straight.
2.
Cradle misalignment on a 6000. Side rail support misalignment on a Sunbird or Grand Am. Section 3 of the 1985 Body Service Manual lists
measurement points to determine proper cradle and underbody alignment.
NOTE:
A difference in the front wheel to rear wheel measurement compared side to side may indicate a "dog track" condition or one front
wheel ahead of the other due to cradle misalignment. A substantial caster difference is an indication of cradle misalignment. Minor
caster difference may be corrected by slotting the tower strut mounting holes. Caster should be equal. Camber may be biased slightly
to offset a lead condition.
3.
Front suspension damage, such as a bent strut.
4.
Tire residual aligning torque. Exchange tires with a known good car to diagnose.
