ASE ASE Manual Drive Train and Axles 2 — Questions and Answers
Question 1: A rear-axle differential makes a howling noise that changes pitch with vehicle speed but not with engine speed. What is the MOST likely cause?
- Worn pinion shaft bearings with incorrect preload
- Improper ring and pinion gear backlash or worn gear teeth (Correct answer)
- Loose ring gear bolts
- Low differential fluid level only
Correct answer: Improper ring and pinion gear backlash or worn gear teeth
A howl that tracks vehicle speed rather than engine speed is characteristic of ring and pinion gear noise from improper backlash, wear, or incorrect contact pattern.
Question 2: When setting up a ring and pinion gear set in a rear axle, what does the gear tooth contact pattern indicate?
- The amount of gear backlash present
- The correct pinion depth and backlash adjustment (Correct answer)
- The ring gear runout
- The differential case bearing preload
Correct answer: The correct pinion depth and backlash adjustment
The contact pattern (checked with gear marking compound) shows whether pinion depth and backlash are set correctly for quiet, durable gear operation.
Question 3: A 4WD vehicle with an open differential on the rear axle gets stuck with one wheel spinning freely. What limited-slip or locking device would MOST effectively prevent this?
- Positraction or limited-slip differential (Correct answer)
- A larger ring and pinion ratio
- A heavier axle housing
- A stiffer anti-roll bar
Correct answer: Positraction or limited-slip differential
A limited-slip or locking differential transfers torque to the wheel with traction rather than allowing all torque to go to the spinning wheel.
Question 4: What fluid is typically required in a limited-slip differential, and why?
- Standard gear oil only, because the clutch packs need no lubrication
- Gear oil with a limited-slip friction modifier additive to prevent chatter (Correct answer)
- Automatic transmission fluid for all limited-slip units
- Engine oil because it has the correct viscosity
Correct answer: Gear oil with a limited-slip friction modifier additive to prevent chatter
Limited-slip differentials use clutch packs that require a friction modifier to control the coefficient of friction and prevent the shudder or chatter that occurs with standard gear oil.
Question 5: A technician measures excessive axle shaft endplay on a semi-floating rear axle. What is the MOST likely cause?
- Worn axle bearing (Correct answer)
- Loose axle flange bolts
- Worn or missing C-clip retainer
- Incorrect differential fluid viscosity
Correct answer: Worn axle bearing
On a semi-floating axle, the axle bearing supports the axle and controls endplay; a worn bearing allows the axle to move axially beyond specification.
Question 6: What is the CORRECT method to check differential bearing preload?
- Measure the torque required to rotate the pinion with a inch-pound torque wrench (Correct answer)
- Check the backlash only — preload is set automatically
- Measure pinion depth with a dial indicator
- Inspect the gear contact pattern only
Correct answer: Measure the torque required to rotate the pinion with a inch-pound torque wrench
Pinion bearing preload is measured as rotating torque (in inch-pounds) using a torque wrench and socket on the pinion nut after the crush sleeve is set.
ASE ASE Manual Drive Train and Axles 2
A rear-axle differential makes a howling noise that changes pitch with vehicle speed but not with engine speed.
What is the MOST likely cause?