NCED Transmission & Drivetrain Systems 3 — Questions and Answers
Question 1: Which planetary gear set member is typically held stationary to achieve a reduction in gear ratio (underdrive)?
- Sun gear
- Ring gear (annulus) (Correct answer)
- Planet carrier
- Output shaft
Correct answer: Ring gear (annulus)
Holding the ring gear stationary while driving the sun gear causes the planet carrier to rotate at a reduced speed, producing an underdrive ratio.
Question 2: A driveshaft equipped with U-joints operates most efficiently when the operating angle is:
- As large as possible to absorb vibration
- Equal and opposite at both ends to cancel velocity fluctuations (Correct answer)
- Set to exactly 90 degrees for maximum torque transfer
- Greater at the rear U-joint than at the front
Correct answer: Equal and opposite at both ends to cancel velocity fluctuations
Equal and opposite U-joint angles cause their inherent velocity fluctuations to cancel each other, resulting in smooth power delivery.
Question 3: What type of joint is used in front-wheel drive axle shafts to accommodate both steering angles and suspension travel without velocity fluctuation?
- Universal joint (U-joint)
- Constant velocity (CV) joint (Correct answer)
- Slip yoke
- Thomas coupling
Correct answer: Constant velocity (CV) joint
CV joints maintain a constant output speed regardless of operating angle, making them ideal for steered, independently suspended drive axles.
Question 4: When diagnosing a clicking noise from the front of a FWD vehicle that increases during tight turns, the most likely cause is:
- Worn transmission output shaft bearing
- Worn or damaged outer CV joint (Correct answer)
- Failing wheel bearing
- Loose drive axle nut
Correct answer: Worn or damaged outer CV joint
A worn outer CV joint produces a clicking or popping sound under load during cornering because its balls and grooves are worn.
Question 5: In a dual-clutch transmission (DCT), the two clutches typically control:
- Forward and reverse gears respectively
- Odd and even gear sets respectively (Correct answer)
- Low-range and high-range gear sets
- Hydraulic pressure and mechanical gear selection
Correct answer: Odd and even gear sets respectively
DCTs use one clutch for odd-numbered gears and one for even-numbered gears, pre-selecting the next gear for near-instant shifts.
Question 6: Transmission fluid that appears dark brown or black and has a burnt odor most likely indicates:
- Normal oxidation from long service intervals
- Overheating causing degradation of friction material and fluid (Correct answer)
- Water contamination from a failed cooler
- Excessive additive concentration from over-filling
Correct answer: Overheating causing degradation of friction material and fluid
Dark, burnt-smelling fluid indicates the transmission has overheated, burning the fluid and friction material debris.
Question 7: Which of the following best describes the purpose of a transfer case in a four-wheel drive vehicle?
- It converts the final drive ratio for improved fuel economy
- It splits drivetrain torque between front and rear axles and provides high/low range (Correct answer)
- It differentiates speed between the left and right rear wheels
- It regulates hydraulic pressure to engage the front axle hubs
Correct answer: It splits drivetrain torque between front and rear axles and provides high/low range
The transfer case receives output from the transmission and distributes it to front and rear driveshafts, often with a low-range gear reduction.
NCED Transmission & Drivetrain Systems 3
Which planetary gear set member is typically held stationary to achieve a reduction in gear ratio (underdrive)?