ASE G1 Auto Maintenance and Light RepairManual Drive Train and AxlesHard
A technician is diagnosing a loud clunking noise coming from the rear of a rear-wheel-drive vehicle, especially when shifting gears or accelerating from a stop. Upon inspection, they find significant rotational play in the driveshaft at the differential input flange. Which component is MOST likely causing this noise?
- ALoose differential cover bolts
- BDamaged axle shaft
- CExcessive differential backlash
- DWorn wheel bearings
Show answer & explanationAnswer & explanation
Correct answer: C. Excessive differential backlash
A clunking noise during gear changes or acceleration, coupled with significant rotational play in the driveshaft at the differential, is a classic symptom of excessive differential backlash. Backlash refers to the clearance between the differential ring and pinion gears.
Why the other options are wrong
- A. Loose differential cover bolts would cause a fluid leak, not rotational play or clunking.
- B. A damaged axle shaft could cause noise or vibration, but significant rotational play at the differential input flange specifically points to internal differential gear issues, not typically the axle shaft itself.
- D. Worn wheel bearings typically cause a humming or growling noise that changes with vehicle speed or cornering, not clunking from driveline play.
Excessive Differential Backlash
Excessive differential backlash refers to too much clearance between the ring and pinion gears within the differential. This leads to free play in the driveline, causing clunking noises during torque changes.
- Causes clunking during acceleration, deceleration, or shifting.
- Identified by significant rotational play at the driveshaft/differential.
- Requires adjustment or replacement of differential components.
- Can accelerate wear of other differential parts.
Memory trick: Clunk from the rear? Check backlash, my dear!