Manual Drive Train and Axles A3 Flashcards

A technician is measuring driveshaft U-joint phasing during driveshaft service. What does incorrect phasing cause?

Answer: Driveline vibration because the velocity variations of each joint do not cancel out

U-joints introduce a cyclic velocity variation as the driveshaft rotates through each revolution. Proper phasing (yokes aligned in the same plane) causes the variations of the front and rear U-joints to cancel each other out. Incorrect phasing causes the variations to add together, creating a twice-per-revolution driveshaft vibration.

A front-wheel-drive vehicle vibrates at highway speed. The vibration is felt in the steering wheel and gets worse with increasing speed but is not affected by turns or steering input. What is the MOST likely cause?

Answer: Out-of-balance front wheels or tires

A vibration that increases with speed, is felt in the steering wheel, and is not affected by turns or steering angle is a classic symptom of wheel and tire imbalance. Imbalance creates a centrifugal force that increases with the square of rotational speed, producing speed-sensitive vibration.

A manual transmission jumps out of 2nd gear under load. All other gears remain engaged. What is the MOST likely cause?

Answer: Weak or broken detent spring for the 2nd gear shift fork

A transmission that pops out of a specific gear under load typically has a worn or broken detent ball and spring for that gear position. The detent provides the positive feel when a gear is selected and holds the shift rail in position. A weak spring allows load-induced vibrations to push the rail out of the engaged position.

What is the correct procedure for checking ring and pinion gear contact pattern during differential setup?

Answer: Apply oil paint to three or four ring gear teeth and observe the contact mark after rotating under load

The gear contact pattern test uses gear marking compound (oil-based paint) applied to ring gear teeth. As the gears are rotated under light resistance, the paint transfers to the pinion teeth in a pattern that reveals the position and quality of tooth contact, allowing shimpack adjustments to achieve proper mesh.

A 4WD vehicle has a vibration that only occurs when in 4WD High range at highway speeds. The vibration is not present in 2WD. What is the MOST likely cause?

Answer: Mismatched tire sizes between front and rear axles

When a 4WD system is engaged on a dry, hard surface, the front and rear axles are locked together. Any difference in effective tire rolling diameter between front and rear axles (from mismatched tire sizes or different wear levels) causes driveline wind-up and vibration as the system tries to resolve the speed mismatch.

During clutch pedal free play adjustment, a technician measures 0.25 inches of free play when the specification is 0.5–1.0 inches. What will result if the vehicle is operated with this condition?

Answer: Release bearing will ride on the pressure plate fingers, causing premature bearing wear

Insufficient clutch pedal free play means the release bearing is in constant contact with the pressure plate release fingers. This causes the release bearing to spin continuously under load, leading to rapid bearing wear, overheating, and eventual bearing failure.