ASE A4 Suspension and SteeringSuspension System Diagnosis and RepairMedium
A technician is diagnosing a vibration that is felt primarily through the seats and floorboard at highway speeds (60-75 mph) but is not significantly affected by braking or accelerating. The vibration is present regardless of whether the vehicle is in gear or coasting. After balancing all four tires, the vibration persists. Which of the following is the MOST likely cause?
- AWarped brake rotors
- BDamaged constant velocity (CV) joint
- CWorn or unbalanced driveshaft
- DLoose wheel bearing
Show answer & explanationAnswer & explanation
Correct answer: C. Worn or unbalanced driveshaft
A vibration felt through the seats and floorboard at highway speeds, unaffected by braking or acceleration, and persisting after tire balancing, strongly points to a driveline component, specifically a worn or unbalanced driveshaft. Driveshaft imbalance typically manifests at higher speeds.
Why the other options are wrong
- A. Warped brake rotors cause vibration primarily during braking.
- B. Damaged CV joints usually cause clicking or clunking noises, especially during turns or acceleration, or a vibration during acceleration, not typically a sustained high-speed vibration unaffected by load.
- D. A loose wheel bearing typically causes a growling/humming noise and potential wheel play, not usually a sustained vibration through the floor at speed after balancing.
Driveshaft Imbalance
An imbalance in the driveshaft, often due to damage, missing weights, or worn universal joints, causes vibrations that are typically felt at higher speeds through the vehicle's body.
- Manifests as high-frequency vibration
- Felt in seat, floor, or steering wheel (less common for driveshaft)
- Not affected by braking or acceleration (unless U-joints are bad)
Memory trick: Speedy shake, check the shaft, or it's a tire's silly craft.