ASE H3 Drive Train (Transit Bus) flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Driveline vibration speed test

Road test at the speed where vibration occurs; if vibration changes with engine RPM it is engine or driven component related; if it changes with vehicle speed it is driveline related.

U-joint operating angle

Measured with a protractor at each joint; canceling angles should be within 1 degree of each other; excessive or unequal angles cause vibration and premature U-joint failure.

Driveshaft runout limit

Measured with a dial indicator at the center and near each end; typical maximum is 0.010 inch (0.25 mm) for a bus driveshaft; replace or straighten if exceeded.

Carrier bearing preload

Set per manufacturer specification; too tight causes bearing overheating, too loose causes vibration and noise; inspect rubber insulator for cracks and sag.

Differential backlash

Measured with a dial indicator at the ring gear tooth; typical specification is 0.005 to 0.015 inch (0.13 to 0.38 mm); excessive backlash indicates worn gears or bearings.

Tooth contact pattern

Checked with marking compound; correct pattern is centered on the drive side and slightly toward the toe; heel contact indicates too little pinion depth shim, toe contact too much.

Axle shaft end play

Checked with a dial indicator; typical maximum is 0.005 to 0.020 inch (0.13 to 0.51 mm); excessive play indicates worn bearings or incorrect shims.

Wheel seal leak

Inspect for gear lube on brake components; a leaking seal can contaminate brake linings and cause pull or reduced braking; replace seal and check axle vent for blockage.

Driveline noise diagnosis

Whine that changes with speed but not engine RPM points to differential or axle bearings; clicking on turns points to CV joints; growl that increases with load points to pinion bearings.

Vibration after repair

Check driveshaft phasing and balance; verify U-joint angles are within specification; ensure slip joint is properly lubricated and splines are aligned; check transmission mount and center bearing.

Pinion bearing preload

Measured with an inch-pound torque wrench at the pinion nut; too little preload causes noise and bearing failure; too much causes overheating; always replace crush sleeve or shims when changing bearings.

Ring gear runout

Measured with a dial indicator at the ring gear; typical maximum is 0.002 to 0.004 inch (0.05 to 0.10 mm); excessive runout causes noise and uneven tooth wear.

Axle housing alignment

Check for bent housing after collision or curb impact; misalignment causes tire wear, vibration, and seal leaks; measure with alignment tools or replace housing if bent.

Driveshaft balance

Check for missing balance weights, dents, or undercoating; imbalance causes vibration at highway speeds; rebalance or replace shaft; mark shaft and yoke before disassembly to maintain balance.

Differential oil level

Check at fill plug hole with vehicle level; oil should be even with bottom of fill hole; low level causes bearing and gear failure; use specified lubricant and check for leaks.

Transmission fluid level check

Check with engine running at operating temperature in Park or Neutral per manufacturer; low level causes slipping and delayed engagement; overfill causes aeration and foaming.

Transmission fluid condition

Dark or burnt fluid indicates overheating or clutch pack wear; milky fluid indicates coolant contamination from a failed cooler; metal debris on the magnet indicates internal wear.

Torque converter stall test

Hold brakes, apply full throttle in gear, record maximum engine RPM; low stall indicates engine or converter stator problems; high stall indicates slipping clutches or low line pressure.

Line pressure test

Connect gauge to pressure port; compare readings in each gear range to specification; low pressure in all ranges indicates pump or pressure regulator; low in one range indicates leaking circuit.

Shift solenoid diagnosis

Measure resistance across solenoid terminals; compare to specification (typically 10 to 30 ohms); open or shorted coil sets a code and causes harsh or missing shifts.

Transmission relearn procedure

After replacing valve body, solenoids, or TCM, perform adaptive relearn; clear adaptive memory and drive vehicle through learn cycle to restore shift quality.

Driveline lubrication

Use specified lubricant; overfilling differential or transmission can cause seal leaks and aeration; underfilling causes bearing and gear failure; check vent for obstruction.

Clutch adjustment

Check pedal free play per specification; excessive free play causes incomplete disengagement and gear clash; insufficient free play causes clutch slippage and release bearing wear.

Cooler line flow test

Disconnect return line and measure flow into container for specified time; low flow indicates restricted cooler or line; flush cooler whenever transmission is replaced to prevent debris contamination.

Transmission mount inspection

Check for cracks, separation, or sag; a failed mount causes vibration, noise, and misalignment of driveline; replace mount and check driveshaft angles after replacement.

Valve body service

Remove, disassemble, and clean valve body; check for stuck valves, worn bores, and debris; replace gaskets and check balls; torque bolts to specification in sequence to prevent warpage.

Transmission filter replacement

Replace filter whenever fluid is changed or transmission is repaired; a clogged filter causes low pressure and slipping; check pan magnet for debris to assess internal wear.

Shift linkage adjustment

Adjust linkage so detents align with transmission lever; misadjustment causes incorrect gear selection, no start in Park, or slipping; check with engine off and parking brake applied.

Transmission temperature check

Use scan tool or infrared thermometer; normal operating temperature is typically 175 to 225°F (80 to 107°C); excessive temperature indicates cooler restriction, low fluid, or heavy load.

Driveline phasing

Yokes on a two-piece driveshaft must be in phase (aligned) to cancel vibration; check alignment marks; incorrect phasing causes vibration and premature U-joint failure.

Transmission adaptive learning

TCM adjusts shift pressures based on driving; after repairs, clear adaptive memory and perform relearn; otherwise harsh or delayed shifts may occur until system relearns.

Differential bearing noise

Growl or rumble that changes with speed and load indicates worn carrier or pinion bearings; check backlash and tooth pattern; replace bearings and reset preload and backlash.