ASE A3 key terms

A friction-lined disc splined to the transmission input shaft. It is clamped between the flywheel and pressure plate to carry engine torque, and released to interrupt power during shifts.

A spring-loaded assembly bolted to the flywheel. Its springs clamp the clutch disc against the flywheel; when the release bearing pushes the release fingers, clamping force is removed and the clutch disengages.

A bearing that rides against the pressure plate release fingers. It is moved by the clutch fork or slave cylinder to release the clamping force on the clutch disc.

A small bearing or bushing in the center of the crankshaft or flywheel. It supports and centers the front end of the transmission input shaft.

A pivoting lever that pushes the release bearing toward the pressure plate when the clutch pedal moves. It may be actuated by a cable, linkage, or hydraulic slave cylinder.

A hydraulic actuator mounted at the bell housing. It converts fluid pressure from the clutch master cylinder into movement of the release bearing or clutch fork.

The small amount of pedal travel or release-mechanism clearance before the release bearing contacts the pressure plate. It lets the clutch fully engage as friction surfaces wear.

A heavy disc bolted to the crankshaft. It provides the friction surface for the clutch disc, carries the starter ring gear, and smooths out engine torque pulses.

A mechanism in a manual transmission that uses friction cones to match gear and shaft speeds before engagement, so the shift sleeve can lock the gear without grinding.

The friction cone ring of a synchronizer. It contacts the gear cone to speed up or slow down the gear, and its chamfered teeth block the sleeve until speeds match.

A forked lever that slides a synchronizer sleeve or shift collar along a shaft to select a gear. It is moved by a shift rail or external linkage.

The shaft in a manual transmission that is driven by the input shaft. Its gears mesh with mainshaft gears to produce the different forward gear ratios.

The output shaft of a manual transmission. It carries the gears and synchronizers and delivers torque to the driveshaft, transfer case, or final drive.

The shaft that receives torque from the clutch disc and carries it into the transmission. Its front end is supported by the pilot bearing in the crankshaft.

A transmission design in which all forward gears stay in mesh with their mating gears at all times. Gears are selected by locking them to the shaft, not by sliding into mesh.

A combined transmission and final drive/differential unit, common in front-wheel-drive cars. It sends torque to the drive wheels through half-shafts with constant velocity joints.

A flexible coupling that lets a driveshaft transmit torque while the shaft angle changes with suspension movement. The common cross-and-yoke type is also called a Cardan joint.

Two universal joints connected by a centering ball and socket. The arrangement cancels the speed fluctuations of a single Cardan joint at large driveshaft angles.

A splined yoke that slides on a splined shaft to change the effective length of the driveshaft as the suspension moves, preventing binding or thrust loads.

The rotational alignment of the universal joint yokes at each end of a driveshaft. Correct phasing lets the joints cancel each other's speed changes and prevents vibration.

A joint that transmits torque at a steady angular velocity through a wide range of angles. It is used on half-shafts and independent suspension axles.

A ball-type constant velocity joint with an inner race, cage, balls, and outer housing. It is commonly used at the wheel end of a front half-shaft.

A constant velocity joint with a three-legged spider and rollers that can plunge in and out. It is commonly used at the inboard end of a half-shaft.

The shaft connecting the transaxle or differential to a driven wheel. It has a constant velocity joint at each end to allow suspension travel and steering.

A flexible rubber or plastic cover that seals a constant velocity joint, holding grease in and keeping dirt and water out. A torn boot causes rapid joint wear.

A gear assembly that divides torque between two driven wheels and lets them turn at different speeds in turns. It also provides the final gear reduction in many axles.

The final drive gear set. The pinion gear drives the larger ring gear, turning torque 90 degrees and multiplying it by the axle ratio.

The small pinion gears mounted on a shaft inside the differential case. They mesh with the side gears and let the two wheels turn at different speeds.

The differential gears splined to the axle shafts. They mesh with the spider gears and transfer torque from the differential case to the axle shafts.

The small clearance between the ring gear and pinion teeth. It allows room for lubricant and heat expansion; too little or too much causes noise and wear.

The force holding the pinion bearings against their races. It is set with shims or a crush sleeve so the pinion turns with a specified amount of drag.

A differential that resists speed differences between the two wheels and sends more torque to the wheel that has traction. It uses clutches, cones, worm gears, or a viscous coupling.

A gearbox mounted behind the transmission in a four-wheel-drive or all-wheel-drive vehicle. It splits torque to the front and rear axles and often provides high and low ranges.

A hub on a part-time four-wheel-drive front axle that locks the wheel to the axle shaft for four-wheel drive and unlocks it to reduce drag in two-wheel drive.

The shaft that carries a wheel and transmits torque from the differential side gear to the wheel hub, either in a solid axle or an independent suspension.

A mechanism that disconnects one front axle shaft from the differential in part-time four-wheel drive so the front differential and driveshaft do not turn in two-wheel drive.

A one-piece axle housing that contains the differential and axle shafts, with a wheel at each end. Both wheels move together over bumps.

A sealed bearing unit that supports the wheel hub. Many modern units also carry the ABS wheel speed sensor ring and are replaced as a complete assembly.