Drivetrain and Transmission Flashcards

What is the purpose of the one-way (sprag/roller) clutch in an automatic transmission?

Answer: To hold or drive a component in one direction while allowing free rotation in the other, enabling smooth shifts

One-way clutches hold planetary gear elements when torque is applied in one direction but freewheel in the other. This provides smooth, overlapping shifts because they apply and release based on rotational direction rather than hydraulic timing.

What does a continuously variable transmission (CVT) use instead of fixed gear ratios?

Answer: A belt or chain running between two variable-diameter pulleys that provide infinite ratio variation

A CVT uses a steel belt or chain running between two conical pulleys. By varying the effective diameter of each pulley, the CVT provides a continuously variable ratio without discrete shift steps, keeping the engine at optimal RPM.

What is the function of the centre support bearing on a two-piece driveshaft?

Answer: To support the driveshaft at the junction of the two sections, maintaining alignment and absorbing vibration

The centre support bearing is a rubber-mounted bearing bolted to the underside of the vehicle at the point where the two driveshaft sections meet. It supports the shaft weight, maintains alignment, and absorbs vibration.

A four-wheel-drive vehicle exhibits a binding sensation during tight turns on dry pavement in 4WD mode. What is the cause?

Answer: Drivetrain windup caused by the front and rear axles being locked together without a centre differential

In part-time 4WD, the transfer case locks the front and rear output shafts together. On dry pavement, the front and rear axles must turn at different speeds in turns. The locked system prevents this, causing drivetrain windup and binding.

What is the function of the shift solenoids in an electronically controlled automatic transmission?

Answer: To act as electrically controlled hydraulic valves that direct fluid flow to engage specific clutch packs as commanded by the TCM

Shift solenoids are electro-hydraulic valves controlled by the TCM. When energized or de-energized in specific combinations, they direct hydraulic fluid to apply or release clutch packs and bands, selecting the appropriate gear.

What causes a driveline vibration at a specific vehicle speed that goes away above or below that speed?

Answer: An unbalanced or bent driveshaft

An unbalanced or bent driveshaft produces a vibration at the specific RPM where the imbalance creates resonance. The vibration occurs at a narrow speed range and disappears at higher or lower speeds.