310T Drivetrain and Transmission 2 — Questions and Answers
Question 1: A Class 8 truck exhibits a harsh 1-2 upshift in an Allison automatic transmission. What is the MOST likely cause?
- Low transmission fluid level
- Faulty turbine speed sensor (Correct answer)
- Worn torque converter clutch
- Clogged transmission cooler line
Correct answer: Faulty turbine speed sensor
A faulty turbine speed sensor provides incorrect shaft speed data, causing the TCM to miscalculate shift timing and produce harsh upshifts.
Question 2: When performing a stall test on a torque converter, what does a stall speed BELOW the manufacturer's specification indicate?
- Slipping clutch packs inside the transmission
- A faulty torque converter stator one-way clutch
- Low engine power or a seized stator (Correct answer)
- Excessive transmission fluid pressure
Correct answer: Low engine power or a seized stator
A stall speed below spec indicates the engine cannot develop enough power, or the stator is seized and is not allowing proper fluid coupling multiplication.
Question 3: Which component in a standard Spicer-style driveshaft prevents vibration caused by the angularity of universal joints?
- Slip yoke
- Companion flange
- Phased yokes (Correct answer)
- Grease fitting
Correct answer: Phased yokes
Phased (timed) yokes ensure the front and rear U-joints operate in the same plane, canceling out speed fluctuations and preventing driveline vibration.
Question 4: A truck technician is diagnosing a manual transmission that pops out of fifth gear under load. What is the MOST probable cause?
- Worn shift fork
- Worn or damaged synchronizer blocker ring
- Excessive mainshaft end play
- Worn detent balls and springs (Correct answer)
Correct answer: Worn detent balls and springs
Worn detent balls and springs cannot hold the shift rail in the selected gear position, allowing the transmission to pop out under load.
Question 5: In a tandem drive axle bogie, what is the purpose of the interaxle differential lock?
- It prevents wheel spin on both drive axles simultaneously
- It locks the ring gear to the axle housing
- It couples both axle input shafts to distribute torque equally regardless of traction (Correct answer)
- It increases the gear ratio between the two axles
Correct answer: It couples both axle input shafts to distribute torque equally regardless of traction
The interaxle differential lock mechanically couples the forward and rear drive axle inputs so torque is equally distributed, preventing one axle from spinning freely when traction is lost.
Question 6: Which type of lubricant is typically specified for a Meritor-style hypoid rear axle?
- SAE 80W-90 GL-4 gear oil
- SAE 75W-140 GL-5 gear oil (Correct answer)
- Dexron ATF
- SAE 30 engine oil
Correct answer: SAE 75W-140 GL-5 gear oil
Hypoid axle gears require GL-5 rated gear oil with extreme-pressure additives, and modern Meritor axles commonly specify SAE 75W-140 synthetic GL-5 for temperature stability.
Question 7: A technician notices the speedometer reads higher than actual vehicle speed on a truck that recently had larger tires installed. What drivetrain calibration is required?
- Recalibrate the ABS module ring gear tooth count
- Adjust the rear axle gear ratio
- Reprogram the vehicle speed sensor (VSS) pulse count in the ECM (Correct answer)
- Install a new driveshaft speed sensor
Correct answer: Reprogram the vehicle speed sensor (VSS) pulse count in the ECM
Larger tires travel farther per revolution, so the ECM's VSS pulse-per-mile calibration must be updated to reflect the new tire circumference.
310T Drivetrain and Transmission 2
A Class 8 truck exhibits a harsh 1-2 upshift in an Allison automatic transmission.
What is the MOST likely cause?