ASE A4 Suspension and SteeringWheel Alignment Diagnosis, Adjustment, and RepairMedium
A technician is performing a four-wheel alignment on a vehicle equipped with an independent rear suspension. The alignment machine indicates a positive thrust angle of +0.3 degrees. The specification is 0.0 degrees +/- 0.1 degrees. Which of the following is the MOST appropriate adjustment to correct this condition?
- AAdjust the rear toe on the left side to reduce the thrust angle.
- BAdjust both rear toe angles equally to bring the thrust angle to zero.
- CAdjust the front toe to compensate for the thrust angle.
- DAdjust the rear toe on the right side to reduce the thrust angle.
Show answer & explanationAnswer & explanation
Correct answer: D. Adjust the rear toe on the right side to reduce the thrust angle.
A positive thrust angle indicates the rear axle is pointing to the right of the vehicle's centerline. To correct this, the right rear wheel needs to be pointed more towards the left (less toe-in or more toe-out, depending on current setting) to bring the thrust line back to zero. Adjusting the right rear toe will directly influence the thrust angle.
Why the other options are wrong
- A. Adjusting the left rear toe would primarily affect the thrust angle in the opposite direction, potentially worsening a positive thrust angle or creating a negative one.
- B. Adjusting both rear toe angles equally would change the total rear toe but might not correct the thrust angle effectively, as thrust is a differential measurement.
- C. Adjusting front toe to compensate for rear thrust angle is a temporary fix that does not correct the underlying rear axle misalignment and can lead to uneven tire wear.
Thrust Angle Adjustment (Independent Rear)
On independent rear suspensions, thrust angle is corrected by adjusting the individual toe settings of the rear wheels to align the rear thrust line with the vehicle's geometric centerline.
- Positive thrust angle means rear points right.
- Negative thrust angle means rear points left.
- Adjust individual rear toe to correct.
Memory trick: Positive thrust means right rear needs a push back.