NAPA - National Automotive Parts Association Certified Mechanic Manual Drivetrain and Axles Questions and Answers — Questions and Answers
Question 1: A customer with a manual transmission vehicle complains of a high-pitched squealing noise that occurs only when the clutch pedal is fully depressed. The noise disappears as soon as the pedal is released. What is the MOST likely cause?
- Worn pilot bearing
- Worn throwout (release) bearing (Correct answer)
- Slipping clutch disc
- A leaking clutch master cylinder
Correct answer: Worn throwout (release) bearing
The throwout bearing, also known as the release bearing, is the component that applies force to the pressure plate fingers to disengage the clutch. It is only under load and spinning when the clutch pedal is depressed. A worn or failing throwout bearing will typically make a squealing or whirring noise under this load, which goes away when the pedal is released.
Question 2: A technician is test-driving a vehicle with a manual transmission and observes that it grinds when shifting into third gear, but all other gears engage smoothly. The clutch is confirmed to be disengaging properly. What is the MOST likely cause of this issue?
- A damaged input shaft bearing
- A bent shift fork for the 1-2 shift rail
- Use of the incorrect type of gear oil
- A worn-out third gear synchronizer assembly (Correct answer)
Correct answer: A worn-out third gear synchronizer assembly
The function of a synchronizer is to match the rotational speed of the selected gear to the speed of the output shaft before the engagement sleeve locks them together. When the friction material on a specific gear's synchronizer ring is worn, it cannot effectively equalize the speeds, causing the teeth on the engagement sleeve to clash with the gear teeth, resulting in a grinding noise. Since the problem is isolated to one gear, it points to a component specific to that gear.
Question 3: A front-wheel-drive vehicle produces a rhythmic clicking or popping noise that is most prominent during sharp, low-speed turns. The noise is not present when driving in a straight line. This symptom is most indicative of a failing:
- Outer Constant Velocity (CV) joint (Correct answer)
- Wheel bearing
- Inner tie rod end
- Lower ball joint
Correct answer: Outer Constant Velocity (CV) joint
The outer Constant Velocity (CV) joint is designed to transmit torque from the transaxle to the wheel while allowing for the wide articulation needed for steering. When the joint wears, the internal balls and cage develop excessive play. During a turn, the angle of the joint increases, and this excessive play causes the internal components to make a distinct clicking or popping sound under load.
Question 4: Which of the following symptoms is MOST commonly associated with a worn universal joint (U-joint) on a rear-wheel-drive vehicle's driveshaft?
- A burning smell after high-speed driving
- A high-frequency whine that changes with road speed
- A clunking sound when shifting from Drive to Reverse (Correct answer)
- A spongy feeling in the brake pedal
Correct answer: A clunking sound when shifting from Drive to Reverse
A worn U-joint has excessive clearance in its needle bearings and cross assembly. When the direction of the driveshaft's rotation is suddenly reversed, such as when shifting from Drive to Reverse or vice-versa, this internal slack is taken up abruptly. This action produces a distinct 'clunk' or 'ping' as the driveshaft engages the differential. This can also cause a vibration at highway speeds.
Question 5: A manual transmission is difficult to shift into any gear when the vehicle is stationary and the engine is running. However, it shifts normally through all gears when the engine is turned off. Which of the following is the MOST likely cause?
- Worn shift forks
- Low transmission fluid level
- Worn synchronizer rings
- A dragging clutch (Correct answer)
Correct answer: A dragging clutch
A dragging clutch is one that does not fully disengage the engine from the transmission's input shaft when the pedal is depressed. With the input shaft still being spun by the engine, the synchronizers are unable to match the speeds of the gears, making it difficult or impossible to shift. When the engine is off, the input shaft is stationary, allowing for easy gear engagement without the need for synchronizers.
Question 6: When setting up a new ring and pinion in a differential, the technician finds the drive-side contact pattern is concentrated high on the tooth, toward the face (or top) of the ring gear teeth. What adjustment is required to correct this pattern?
- Increase backlash
- Decrease pinion depth (move pinion away from ring gear) (Correct answer)
- Decrease backlash
- Increase pinion depth (move pinion toward ring gear)
Correct answer: Decrease pinion depth (move pinion away from ring gear)
The position of the contact pattern between the face (top) and flank (root) of the ring gear tooth is controlled by the pinion depth. A pattern that is too high on the tooth (face contact) indicates the pinion is too far away from the ring gear centerline. To correct this, the pinion depth must be decreased by moving the pinion away from the ring gear, typically by removing shims from behind the inner pinion bearing race.
NAPA - National Automotive Parts Association Certified Mechanic Manual Drivetrain and Axles Questions and Answers
A customer with a manual transmission vehicle complains of a high-pitched squealing noise that occurs only when the clutch pedal is fully depressed.
The noise disappears as soon as the pedal is released.
What is the MOST likely cause?