ASE A4 Suspension and SteeringSuspension System Diagnosis and RepairMedium
A technician is performing a pre-alignment inspection on a vehicle with a MacPherson strut front suspension. The customer reports a 'popping' noise from the front end when turning the steering wheel sharply at low speeds. During the inspection, the technician notices that the coil spring on the affected side appears to be 'twisted' relative to its normal seated position on the strut. Which component is MOST likely at fault?
- AWorn lower control arm bushing
- BLoose tie rod end
- CLeaking strut cartridge
- DSeized upper strut bearing
Show answer & explanationAnswer & explanation
Correct answer: D. Seized upper strut bearing
A seized upper strut bearing prevents the coil spring and strut assembly from rotating smoothly with the steering knuckle. When turning, the spring binds, builds tension, and then releases with a 'popping' noise as it overcomes the resistance.
Why the other options are wrong
- A. Worn lower control arm bushings typically cause clunking or excessive movement, not a popping noise specifically related to steering rotation.
- B. A loose tie rod end would cause play in the steering and possibly clunking, but not a popping noise specifically from the coil spring twisting.
- C. A leaking strut cartridge primarily affects ride quality and damping, leading to a bouncy ride or thumping, not a popping noise during steering.
MacPherson Strut Bearing Failure
The upper strut bearing allows the MacPherson strut and coil spring to rotate smoothly with the steering knuckle. Failure leads to binding and noise during steering.
- Located at the top of the strut mount.
- Allows steering rotation without spring binding.
- Failure causes popping, grinding, or groaning noises when turning.
- Can lead to premature tire wear or steering issues.
Memory trick: The MacPherson strut is a tower of components that needs to turn freely at the top.