Transmission & Drivetrain Systems Flashcards

What is the function of the valve body in an automatic transmission?

Answer: It is a hydraulic control center that directs fluid to engage clutches and bands

The valve body routes pressurized transmission fluid through a network of passages and valves to activate the correct clutch packs and bands for each gear.

A vibration felt in the vehicle at highway speeds that is NOT related to engine RPM is most likely caused by:

Answer: An imbalanced or damaged driveshaft

Driveshaft imbalance or damage produces a vehicle-speed-dependent vibration that does not change with engine RPM changes in the same gear.

Which automatic transmission component prevents the engine from being used as a braking force in lower gears unless manually selected?

Answer: One-way (sprag) clutch or roller clutch

One-way clutches allow rotation in only one direction; they freewheel during engine braking unless a friction element overrides them in a manually selected lower range.

The 'creep' behavior of a vehicle with an automatic transmission at idle in Drive is caused by:

Answer: Fluid coupling torque multiplication in the torque converter at low speeds

At idle, the torque converter still transmits some torque through fluid coupling, causing slight forward movement unless the brakes resist it.

When replacing a clutch disc on a rear-wheel drive vehicle, technicians should also inspect the:

Answer: Flywheel or flexplate for wear, cracks, and heat spots

A worn clutch often glazes or damages the flywheel surface, which must be resurfaced or replaced to ensure the new clutch disc wears evenly.

An electronic automatic transmission that fails to upshift out of first gear likely has a faulty:

Answer: Turbine speed sensor (input shaft speed sensor)

The input shaft speed sensor provides the TCM with turbine/input shaft speed; if missing or erroneous, the TCM cannot calculate slip ratio and defaults to limp mode in first gear.

What distinguishes a viscous coupling unit (VCU) from a mechanical limited-slip differential?

Answer: A VCU transfers torque through shear forces in a viscous silicone fluid between rotating plates

Viscous couplings rely on the resistance of thick silicone fluid to shear between closely spaced plates to transfer torque proportional to speed difference.