ASE H8 Preventive Maintenance & Inspection (Transit Bus) common mistakes
ASE H8 Preventive Maintenance & Inspection (Transit Bus) · Understand the traps and how to avoid them.
Starts the PM inspection at the items they expect to fail, then initials the untested lines at the end and writes 'OK' instead of recording tread depth, brake stroke, torque, or battery conductance values.
Time pressure and familiarity make the inspection sheet a form to complete rather than a sequence to work; backfilling is faster than walking the bus in order and writing numbers.
What to do instead
Work the printed form top-to-bottom, initial and record the measured value with units on each line before moving on, and note the specification used. Have a lead technician re-walk a sample of closed forms against the bus before release.
Manually readjusts an automatic slack adjuster to bring pushrod stroke back into specification and releases the bus.
Manual slacks were adjusted this way for years, and turning the adjusting hex is quick; the stroke looks fixed on recheck, so the underlying cause is never investigated.
What to do instead
Treat an out-of-adjustment automatic slack as a symptom. Inspect the S-cam bushings, return spring, chamber, mounting bracket, and pushrod for wear or looseness, correct the cause, then verify stroke without altering the adjuster setting.
Measures pushrod stroke without confirming chamber size and type, application pressure, or pushrod angle, then passes or condemns the brake on that single reading.
Stroke limits differ by chamber size and are only valid at the specified application pressure and angle; a reading taken at the wrong pressure or off-angle falls into the wrong column of the limit table.
What to do instead
Identify the chamber size and type from the vehicle, release spring brakes, build to the manufacturer's specified application pressure, measure stroke at the same pushrod angle each time, and compare with the correct limit before deciding.
Signs off the air system after the dash gauge holds pressure, without timing a leak-down, draining reservoirs, checking dryer purge, or verifying the low-pressure warning and spring-brake application.
A steady gauge at curb idle looks like a pass, and the full leak-down sequence is slow; draining tanks and watching the dryer are easy to skip when the bus is needed.
What to do instead
Run the complete PM air sequence: record governor cut-in and cut-out, time leak-down with brakes released and applied against the allowable rate, drain all reservoirs, confirm dryer purge and heater operation, and verify warning buzzer and emergency spring-brake apply.
Judges battery condition from open-circuit voltage or a hydrometer reading taken just after charging and returns the bus without a load or conductance test.
Surface charge gives a falsely high voltage, and a charged battery can still lack cranking capacity; a no-start complaint may also be a parasitic draw, not a bad battery.
What to do instead
Remove surface charge, perform a conductance or load test at the specified load and temperature, check charging voltage with accessory loads on, and test for parasitic draw whenever the complaint is a no-start or slow crank.
Checks tread depth at one spot on each tire and runs lug nuts on with an impact wrench, checking torque only if a wrench happens to be nearby.
A single reading misses edge wear and flat spots, and impact tightening feels faster and 'tight enough'; over-torque stretches studs and can distort drums and wheels.
What to do instead
Measure tread at multiple points across each groove, inspect both sidewalls, valve hardware, and wheel for cracks, then torque lug nuts with a calibrated wrench in the specified star pattern and recheck after the road test.
Greases the U-joints and calls the driveline good without checking driveshaft phasing, slip-joint play, center bearing condition, or differential fluid level and breather.
Greasing is the visible, familiar task; phasing marks, slip spline play, and breather condition are easy to overlook when the bus is on the ground and time is short.
What to do instead
Before greasing, mark and verify shaft phasing, check U-joint and slip-joint play by hand, inspect the center bearing and mounts, then check differential level at the fill plug with a finger or probe and confirm the breather is clear.
Checks transmission fluid and engine oil with the engine off and cold and tops off coolant from the bulk hose without confirming the specified fluid or mix ratio.
Passenger-car habits carry over, but many transit powertrains require the engine running in a specific range at operating temperature; bulk hoses may carry the wrong coolant or fluid specification.
What to do instead
Follow the OEM level-check procedure for engine state, gear range, and temperature; use only the specified fluid or pre-mixed coolant; fill to the mark rather than the filler neck; and verify coolant condition with a refractometer and test strips.
Inspects belts and hoses only from above with a flashlight and signs off the engine compartment without checking the charge-air cooler, engine mounts, or for fuel, coolant, and oil leaks.
The top of the engine is reachable from the aisle or curb, while the cooler, mounts, and rear-of-engine leaks require a creeper and a light; they go uninspected.
What to do instead
Put the bus on a creeper inspection and check from below: belt ribs and tensioner travel, hose condition by squeezing, charge-air cooler for cracks and oil mist, mount condition, and the rear of the engine, turbo, and fuel lines for staining or drips.
Checks the HVAC only by confirming the blower runs and the air feels cold, without measuring vent temperature, inspecting filters and coils, or cycling the dampers.
Cold air by hand feels like a pass, and a full HVAC check requires gauges, a thermometer, and time in the curb or roof unit; filters and coils are out of sight.
What to do instead
Measure vent temperature against ambient after stabilization, verify charge with manifold gauges, inspect and replace filters, clean condenser and evaporator coils, and cycle the fresh-air and return dampers through every mode while checking airflow at passenger outlets.