Drivetrain and Transmission Flashcards

What is the purpose of the transmission valve body?

Answer: To direct hydraulic fluid flow through a series of valves and passages to control clutch application, shift timing, and line pressure

The valve body is the hydraulic control centre of an automatic transmission. It contains numerous spool valves, check balls, and fluid passages that direct pressurized ATF to apply and release clutch packs and bands in the correct sequence.

What does the ring and pinion gear ratio in a differential determine?

Answer: The final drive torque multiplication and the relationship between driveshaft speed and axle speed

The ring and pinion ratio (e.g., 3.73:1) determines how many times the driveshaft rotates for each revolution of the axle. A numerically higher ratio provides more torque multiplication but lower top speed, and vice versa.

What is the purpose of the clutch pilot bearing (pilot bushing)?

Answer: To support and centre the front end of the transmission input shaft in the crankshaft

The pilot bearing is pressed into the end of the crankshaft and supports the front tip of the transmission input shaft, keeping it centred and aligned with the crankshaft. A worn pilot bearing causes noise when the clutch pedal is depressed at idle.

What is the function of the accumulator in an automatic transmission hydraulic circuit?

Answer: To cushion the application of a clutch pack by temporarily absorbing hydraulic pressure, providing smooth shift engagement

Accumulators use a spring-loaded piston in a bore to temporarily absorb some of the apply pressure during a shift, cushioning the engagement of the clutch pack for a smooth, controlled shift feel.

What causes a clutch to chatter during engagement?

Answer: Oil contamination on the clutch disc, warped disc or flywheel, worn disc damper springs, or loose engine/transmission mounts

Clutch chatter is a grabbing/vibrating sensation during engagement. Common causes include oil or grease on the friction surfaces, a warped or heat-checked flywheel, a warped clutch disc, broken disc damper springs, or loose mounts.

What is the purpose of the speed sensor(s) on an automatic transmission?

Answer: To provide the TCM with input and output shaft speed data for calculating gear ratio, shift timing, and detecting slippage

Input (turbine) and output speed sensors provide the transmission control module (TCM) with rotational speed data. The TCM calculates the actual gear ratio, commands shifts at proper points, and detects clutch slippage by comparing the two speeds.