Drive Train Systems Flashcards

A truck with a tandem-drive axle setup is operating in slippery conditions. To improve traction, the driver engages the inter-axle differential lock (power divider). What is the primary function of this component?

Answer: It locks the differential action between the forward and rear axles, forcing both driveshafts to rotate at the same speed.

The inter-axle differential lock, or power divider, is designed to overcome a loss of traction on one of the tandem axles. In normal (unlocked) operation, it allows the forward and rear axles to rotate at different speeds, which is necessary for turning. When locked, it mechanically connects the two axle driveshafts, forcing them to turn at the same speed and ensuring that torque is sent to both axles, even if one axle has lost traction.

A technician is diagnosing a heavy-duty truck with a manual, non-synchronized transmission. The driver reports a grinding noise and difficulty engaging first and reverse gears only when starting from a complete stop. What is the MOST likely cause of this issue?

Answer: A failing or improperly adjusted clutch brake.

The clutch brake's specific function is to stop the transmission input shaft from spinning when the clutch pedal is fully depressed. This allows for smooth, non-grinding engagement of non-synchronized gears (typically first and reverse) from a standstill. If the clutch brake is worn out or out of adjustment, the input shaft will continue to rotate, causing the gears to clash upon engagement.

While road testing a truck, a technician notices a new, speed-dependent vibration that feels like one shake for every revolution of the driveshaft. This type of vibration is classified as what?

Answer: A first-order vibration.

A first-order driveshaft vibration causes a single shake or disturbance for each complete revolution of the driveshaft. This is typically caused by an imbalance (like a thrown balance weight), a dented shaft, or an out-of-round component rotating at driveshaft speed.

A technician is diagnosing a powershift transmission that exhibits harsh, clunky shifting between all gears. The fluid level and quality are correct, and there are no fault codes related to sensors or solenoids. Which of the following components is MOST likely at fault?

Answer: The valve body.

The valve body is the hydraulic control center of the powershift transmission. If it becomes worn or contains sticking spools or valves, it can cause harsh or erratic gear changes. While other components can cause issues, clunky shifting across all gears often points to a systemic hydraulic control problem originating in the valve body.

When inspecting a driveline for vibration, a technician finds that the U-joint operating angles at the transmission output and the differential input are not within ½° of each other. This condition is most likely to cause what type of failure?

Answer: A second-order vibration and premature U-joint wear.

Incorrect driveline angles, where the operating angles are not equal and opposite, cause the driveshaft to speed up and slow down twice per revolution. This creates a second-order vibration. This constant fluctuation in speed also puts excessive stress on the U-joint needle bearings, leading to premature wear and failure.

A driver reports that when attempting to get out of a muddy area, only one wheel on the forward tandem axle and one wheel on the rear tandem axle spin, and the truck loses all traction. The inter-axle lock is functioning correctly. What additional system must be engaged to provide power to the wheels with traction?

Answer: The full differential lock (cross-lock).

The inter-axle lock ensures both axles receive power. However, the standard differential in each axle will still send power to the wheel with the least resistance. A full differential lock, or cross-lock, locks the spider gears within the axle differential, forcing both wheels on that axle to turn at the same speed. Engaging this provides maximum traction by ensuring all locked wheels rotate together.