ASE A4 Suspension and SteeringWheels and Tires Diagnosis and RepairMedium
A technician is diagnosing a vehicle with a severe vibration that occurs only during braking. The vibration is felt strongly through the brake pedal and steering wheel. After inspecting the brake system, the technician determines the brake rotors are warped. What is the MOST likely underlying cause of the warped brake rotors?
- AExcessive positive caster.
- BImproper wheel balancing.
- CImproper wheel lug nut torque.
- DWorn suspension bushings.
Show answer & explanationAnswer & explanation
Correct answer: C. Improper wheel lug nut torque.
Improper or uneven lug nut torque is a very common cause of warped brake rotors. Uneven clamping force from the lug nuts can distort the rotor, leading to thickness variations or lateral runout that causes pulsation during braking.
Why the other options are wrong
- A. Excessive positive caster affects steering feel and stability, not brake rotor warping or braking vibration.
- B. Improper wheel balancing causes vibration while driving, not specifically during braking.
- D. Worn suspension bushings can cause clunking, wandering, or uneven tire wear, but do not directly cause brake rotor warping.
Warped Rotor Causes
Warped brake rotors, which cause pulsation during braking, are often caused by improper lug nut torque, aggressive braking leading to excessive heat, or uneven cooling.
- Pulsation felt in brake pedal/steering wheel
- Commonly caused by uneven lug nut torque
- Can also be caused by overheating/uneven cooling
Memory trick: Pulsating pedal? Check the torque, not just the rotor!