ASE A4 Suspension and SteeringWheel Alignment Diagnosis, Adjustment, and RepairMedium
A vehicle owner complains of a 'crab-walking' sensation and an off-center steering wheel, even when driving straight. The alignment machine shows a rear thrust angle of -0.7 degrees. The specification for thrust angle is 0.0 degrees +/- 0.2 degrees. All other alignment angles are within specification. Which of the following best describes the vehicle's condition?
- AThe vehicle is experiencing excessive front-end wander.
- BThe vehicle is dog-tracking with the rear of the vehicle shifted to the right.
- CThe vehicle has a severe positive caster split.
- DThe vehicle is dog-tracking with the rear of the vehicle shifted to the left.
Show answer & explanationAnswer & explanation
Correct answer: D. The vehicle is dog-tracking with the rear of the vehicle shifted to the left.
A negative thrust angle (-0.7 degrees) indicates that the rear axle is pointing to the left of the vehicle's centerline. This causes the vehicle to 'dog-track' (move sideways) with the rear of the vehicle shifted to the left. To travel straight, the driver must turn the steering wheel slightly to the left, resulting in an off-center steering wheel.
Why the other options are wrong
- A. Front-end wander is typically associated with insufficient positive caster, not thrust angle.
- B. A positive thrust angle would cause the rear to shift right.
- C. A caster split causes vehicle pull and poor returnability, not dog-tracking or an off-center steering wheel due to thrust.
Thrust Angle and Dog-Tracking
Thrust angle is the angle of the rear axle relative to the vehicle's centerline. A non-zero thrust angle causes the vehicle to 'dog-track' – travel with the rear of the vehicle offset to one side.
- Positive thrust angle: rear axle points right, rear shifts right.
- Negative thrust angle: rear axle points left, rear shifts left.
- Always results in an off-center steering wheel when driving straight.
Memory trick: Thrust negative, rear goes left; like a crab, it's put to the test!