ASE A4 Suspension and SteeringSuspension System Diagnosis and RepairMedium
A technician is diagnosing a vehicle with a MacPherson strut front suspension that exhibits a 'popping' or 'binding' noise from the front left wheel when turning the steering wheel sharply at low speeds. The noise is also sometimes heard when going over small bumps. A visual inspection reveals no play in the ball joints or tie rod ends, and the strut itself shows no leaks. Which of the following is the MOST likely cause of the noise?
- ADamaged coil spring insulator.
- BLoose wheel lug nuts.
- CWorn lower control arm bushing.
- DSeized upper strut mount bearing.
Show answer & explanationAnswer & explanation
Correct answer: D. Seized upper strut mount bearing.
A seized or worn upper strut mount bearing is a very common cause of 'popping' or 'binding' noises when turning the steering wheel in a MacPherson strut suspension. The bearing allows the strut to rotate with the steering, and if it's seized, the spring can bind and release with a pop.
Why the other options are wrong
- A. A damaged coil spring insulator can cause a squeak or rub, but usually not a distinct 'popping' or 'binding' when turning.
- B. Loose wheel lug nuts would cause a clunking noise, wheel wobble, and potentially dangerous wheel separation, not a popping specifically related to steering input.
- C. Worn lower control arm bushings typically cause clunking noises, especially under braking/acceleration or over larger bumps, not specific popping when turning.
Strut Mount Bearing Failure
The upper strut mount bearing allows the MacPherson strut to rotate with the steering knuckle. Failure results in binding, popping, or groaning noises during steering.
- Enables strut rotation for steering
- Wear causes popping/groaning noise
- Affects steering feel and noise
Memory trick: Turning and popping, a strut mount's plea, the bearing's seized, it's plain to see!