Transmission and Driveline Service
What the candidate must know
This domain covers servicing automatic transmissions (including torque converters), clutches, driveshafts, and differentials on transit buses. Candidates must understand fluid type and level checks, filter service, cooler flow, and the consequences of contamination. Know torque-converter operation, lockup clutch function, and how a stalled or slipping converter shows up as heat and poor performance. Understand clutch adjustment and free play on manual applications, release bearing and pilot bearing function, and proper driveshaft installation including phasing and fastener torque. Differential service includes lubricant level and type, vent inspection, and recognizing noise patterns (whine on acceleration vs. deceleration).
Traps in questions
Frequent traps: using the wrong fluid specification, overfilling a transmission, ignoring cooler contamination after a failure, and reusing fasteners that are torque-to-yield. Another trap is assuming a noise is internal when a worn U-joint or bad mount is the cause. Questions may ask what to do after a converter failure - the answer usually includes flushing the cooler and lines.
Worked example / rule of thumb
After a transmission failure that generated debris, the correct service includes replacing the filter, flushing the cooler and lines, and verifying cooler flow before return to service. Rule of thumb: any internal transmission failure that produces debris requires cooler-circuit cleaning, or the new unit will be contaminated.
Service practice
Use the specified fluid, verify level at the specified temperature and procedure, torque fasteners to spec, and road-test to confirm shift quality and cooler operation.