ASE A4 Suspension and SteeringWheel Alignment Diagnosis, Adjustment, and RepairMedium
A technician is performing a four-wheel alignment on a vehicle and observes that the rear thrust angle is -0.75 degrees. The manufacturer's specification for thrust angle is 0.0 degrees ±0.25 degrees. Which of the following conditions is MOST likely indicated by this measurement?
- AThe front axle is shifted to the left relative to the vehicle's centerline.
- BThe rear axle is shifted to the right relative to the vehicle's centerline.
- CThe front axle is shifted to the right relative to the vehicle's centerline.
- DThe rear axle is shifted to the left relative to the vehicle's centerline.
Show answer & explanationAnswer & explanation
Correct answer: D. The rear axle is shifted to the left relative to the vehicle's centerline.
A negative thrust angle indicates that the rear axle is pointing to the left of the vehicle's true centerline. This means the rear axle is effectively shifted to the left or 'dog-tracking' to the left.
Why the other options are wrong
- A. Thrust angle specifically refers to the rear axle's alignment, not the front axle.
- B. A positive thrust angle would indicate the rear axle is shifted to the right.
- C. Thrust angle specifically refers to the rear axle's alignment, not the front axle.
Thrust Angle
The angle between the vehicle's geometric centerline and the thrust line (the direction the rear wheels are pointing). It indicates whether the rear axle is parallel to the front axle and perpendicular to the centerline.
- Positive thrust angle: rear axle points right.
- Negative thrust angle: rear axle points left.
- Ideally, thrust angle should be 0 degrees.
- Impacts steering wheel centering and 'dog-tracking'.
Memory trick: Negative thrust means the rear is 'thrusting' left, like a left hook.