310S Drivetrain and Transmission 3 — Questions and Answers
Question 1: What is the function of the limited-slip differential (LSD)?
- To provide additional gear reduction
- To limit the speed difference between the two drive wheels, sending more torque to the wheel with traction (Correct answer)
- To disconnect the driveshaft at high speed
- To reduce differential gear noise
Correct answer: To limit the speed difference between the two drive wheels, sending more torque to the wheel with traction
An LSD uses clutch packs, viscous coupling, or helical gears to limit the speed difference between the two axle shafts. When one wheel loses traction, more torque is directed to the wheel with grip.
Question 2: What does it mean when an automatic transmission 'flares' between shifts?
- The engine revs drop sharply between gears
- The engine RPM increases momentarily between gears because the oncoming clutch applies too late or the off-going clutch releases too early (Correct answer)
- The transmission shifts too quickly
- The torque converter locks up during a shift
Correct answer: The engine RPM increases momentarily between gears because the oncoming clutch applies too late or the off-going clutch releases too early
Flaring is a brief RPM increase during a shift, indicating the off-going clutch released before the oncoming clutch fully applied. This overlap issue can be caused by low line pressure, worn clutches, or valve body problems.
Question 3: What is the purpose of the dual-mass flywheel (DMF)?
- To increase engine compression
- To absorb and isolate torsional vibrations between the engine and transmission, reducing drivetrain harshness (Correct answer)
- To reduce the weight of the clutch assembly
- To improve clutch pedal feel
Correct answer: To absorb and isolate torsional vibrations between the engine and transmission, reducing drivetrain harshness
The DMF consists of two masses connected by springs and dampers. It absorbs the power pulses and torsional vibrations from the engine, providing smoother power delivery to the transmission and reducing gear rattle.
Question 4: What causes a whining noise from the rear differential that changes with vehicle speed?
- Low tire pressure
- Worn or improperly adjusted ring and pinion gear set (Correct answer)
- A faulty wheel speed sensor
- Worn brake pads
Correct answer: Worn or improperly adjusted ring and pinion gear set
Differential whine is caused by wear or improper backlash/contact pattern adjustment of the ring and pinion gears. The noise changes pitch with vehicle speed because the gear speed changes, and may differ on drive versus coast.
Question 5: What is the function of the transmission fluid cooler?
- To warm the transmission fluid faster during cold starts
- To remove heat from the transmission fluid, maintaining operating temperature and extending fluid and component life (Correct answer)
- To filter contaminants from the transmission fluid
- To increase transmission fluid pressure
Correct answer: To remove heat from the transmission fluid, maintaining operating temperature and extending fluid and component life
The transmission cooler (typically integrated in the radiator or a standalone unit) removes excess heat from ATF. Maintaining proper fluid temperature is critical because heat is the primary cause of transmission failure.
Question 6: A front-wheel-drive vehicle exhibits a humming noise that changes with vehicle speed but not engine RPM. The noise changes tone when swerving left or right. What is the most likely cause?
- A worn CV joint
- A worn wheel bearing (Correct answer)
- A faulty alternator bearing
- Tire tread noise
Correct answer: A worn wheel bearing
A speed-dependent humming that changes with lateral load (swerving) is characteristic of a worn wheel bearing. Swerving loads or unloads the bearing, changing the noise. The sound does not change with engine RPM since it is driven by wheel speed.
310S Drivetrain and Transmission 3
What is the function of the limited-slip differential (LSD)?