Drivetrain and Transmission Flashcards

A technician is investigating a complaint of clutch slippage, which is most noticeable when the truck is pulling a heavy load up a grade. Which of the following is the MOST likely cause?

Answer: Weak pressure plate springs

Weak pressure plate springs reduce the clamping force on the clutch disc, allowing it to slip against the flywheel under high torque conditions. [26] Excessive free play would typically cause issues with clutch release, not slippage. A worn clutch brake affects shifting into gear from a stop, and a misaligned input shaft would cause vibration or shifting difficulties.

What is the primary function of the inter-axle differential (power divider) on a tandem-axle truck when it is unlocked?

Answer: To allow for speed differences between the forward and rear axles when turning

When a truck turns, the rear axle of the tandem set travels a slightly different path than the forward axle. The primary function of the inter-axle differential in its normal, unlocked state is to compensate for this speed difference, which prevents driveline wind-up and excessive tire wear. [1, 15] The lock feature is used to prevent this differentiation for increased traction, but that is not its primary, unlocked function.

A driver reports that their truck, equipped with an Automated Manual Transmission (AMT), intermittently fails to engage a starting gear from neutral. Diagnostic trouble codes point to a fault in the gear selection system. Which of the following components is the MOST likely cause?

Answer: A faulty electronic shift actuator

AMTs use electronic actuators (motors or solenoids) to physically move the shift forks and engage gears based on commands from the Transmission Control Module (TCM). A failure or intermittent fault in one of these actuators would directly prevent the transmission from selecting and engaging a gear. [33] While other issues could cause shifting problems, a gear selection fault code points most directly to the component that performs the physical selection.

When assembling a multi-piece driveshaft, which of the following is MOST critical for preventing driveline vibrations?

Answer: Aligning the yokes on connecting shafts so they are in phase

Universal joints create a non-uniform rotational velocity when operating at an angle. To cancel out this speed fluctuation and prevent second-order vibrations, the yokes at each end of a connecting shaft must be correctly aligned, or "in phase" with one another. [9, 27] Misalignment is a primary cause of driveline vibration. While the other options are good practices, correct phasing is the most critical for vibration prevention.

In a heavy-duty automatic transmission, what is the primary role of the torque converter?

Answer: To act as a fluid coupling and multiply engine torque

The torque converter is a fluid coupling that transfers power from the engine to the transmission's input shaft. [5, 18, 25, 29] Its key advantage is the ability to multiply engine torque when there is a large speed difference between the engine and transmission (e.g., during acceleration from a stop), which improves vehicle performance under load.

A technician is road-testing a truck with a manual transmission and hears a distinct growling noise in all reduction gears. The noise disappears completely when the transmission is shifted into direct drive (1:1 ratio). What is the MOST likely source of the noise?

Answer: Worn countershaft (layshaft) bearings

In all reduction and overdrive gears, power is transmitted from the input shaft to the countershaft, and then to the output shaft. In direct drive (1:1), the input shaft is locked directly to the output shaft, so the countershaft gears and bearings are not under load. If the noise is present in all gears except direct drive, it indicates a problem with a component that is loaded in those gears but not in direct drive, which points directly to the countershaft bearings or gears. [12]