ASE S3 Drive Train (School Bus) key terms

The complete group of parts that carries engine power to the wheels, including the clutch or torque converter, transmission, driveshaft, differential, and axle shafts.

The rotating parts that transfer power from the transmission output to the drive wheels, such as the driveshaft, universal joints, slip yoke, and differential input.

The engine plus all components that deliver its power to the road, including transmission, driveline, and final drive. Broader than drivetrain alone.

The ratio of driveshaft revolutions to axle shaft revolutions, set by the ring and pinion gears, which multiplies torque and affects vehicle speed and fuel economy.

A number expressing how many times the driveshaft turns for each single turn of the wheels, determined by dividing ring gear teeth by pinion gear teeth.

The matched gear set in a drive axle that turns power ninety degrees and provides the final gear reduction between the driveshaft and the axle shafts.

The fore-aft setting of the pinion gear in the axle housing, controlled by shims, that positions the pinion for correct tooth contact with the ring gear.

The small measured clearance between meshing gear teeth, such as ring and pinion or differential side gears, that allows lubricant film and prevents binding.

The mark left on ring gear teeth by a marking compound during setup, used to judge whether pinion depth and backlash are correct.

A gear assembly that lets the drive wheels turn at different speeds during turns while still delivering torque to both, typically using side gears and pinion gears in a carrier.

A differential that restricts speed difference between the two drive wheels, often with clutches or cones, to improve traction on slippery or uneven surfaces.

An additive blended into certain axle lubricants that adjusts clutch friction characteristics in limited slip differentials to prevent chatter and noise during turns.

The small pinion gears mounted on the differential pinion shaft that mesh with side gears and allow the two axle shafts to rotate at different speeds.

The differential gears splined to each axle shaft that mesh with the spider gears and transmit torque to the wheels while permitting speed differentiation.

A bearing that supports the differential carrier assembly inside the axle housing and must be preloaded correctly during setup.

A specified crushing or shimming force applied to the pinion bearings so they run without looseness, set with a collapsible spacer or shim pack and checked by rotational torque.

Gear oil formulated for the final drive, rated by viscosity and service classification, that lubricates gears and bearings and may require limited slip additive.

An axle shaft that carries only driving torque, with wheel load supported by the housing through two wheel bearings, allowing shaft removal without jacking the vehicle.

An axle shaft that transmits torque and also supports part of the vehicle weight, common on lighter rear axles, where a broken shaft can let the wheel leave the housing.

The shaft that connects the differential side gear to the wheel hub and delivers torque to the drive wheel.

The tubular shaft that carries torque from the transmission or transfer case to the drive axle, often in one or two pieces with universal joints and a slip yoke.

A cross and bearing assembly that lets a rotating shaft transmit torque through a changing angle, commonly used at each end of a driveshaft.

A splined coupling at the driveshaft end that slides in and out to absorb changes in shaft length as the suspension moves.

The correct alignment of the yokes on a two piece or multi joint driveshaft so their universal joint angles cancel vibration.

Unwanted shaking or buzzing felt in the vehicle caused by imbalance, worn joints, incorrect angles, or bad mounts in the rotating driveline parts.

The working angle between the transmission output, driveshaft, and pinion, which must be kept within specification to avoid vibration and joint wear.

A rubber cushioned bearing that supports the middle of a two piece driveshaft and damps vibration while allowing slight flex.

A friction assembly that engages and disengages engine power to the manual transmission, using a pressure plate, disc, release bearing, and flywheel.

A bearing that pushes against the pressure plate fingers when the clutch pedal is applied, disengaging the clutch disc from the flywheel.

The small clearance between the release bearing and pressure plate fingers that ensures the clutch fully engages when the pedal is released.

A cone and sleeve mechanism inside a manual transmission that matches gear speeds before engagement so gears can be selected without clashing.

A lever inside a manual transmission that slides the synchronizer sleeve to engage or disengage a gear.

A gearbox in which the driver selects gear ratios through a shifter and clutch, using sliding or constant mesh gears with synchronizers.

A fluid coupling with an impeller, turbine, and stator that transmits and multiplies engine torque in an automatic transmission and allows the engine to idle in gear.

The fixed reaction member inside a torque converter, mounted on a one way clutch, that redirects fluid to multiply torque at low speed.

A friction clutch inside the torque converter that locks the turbine to the impeller at cruise to eliminate slip and improve efficiency.

The hydraulic oil in an automatic transmission that transmits pressure, lubricates, cools, and applies clutches and bands, specified by type and level.

A hydraulic control block containing spools and valves that directs fluid pressure to shift valves, clutches, and bands in an automatic transmission.

An electrically operated valve controlled by the transmission computer that directs fluid to shift valves or apply devices for gear changes.

The computer that monitors inputs such as speed and throttle and commands shift solenoids and line pressure in an automatic transmission.

The main hydraulic pressure supplied by the transmission pump that is regulated and used to apply clutches and bands.

A clamping friction strap inside an automatic transmission that holds a drum stationary to establish a gear ratio, adjusted by a servo.

A controlled drive to observe shift quality, noise, vibration, and speedometer or ratio behavior before and after drivetrain repairs.

A stored alphanumeric code set by a control module when it detects an out of range condition in a monitored circuit or system.