Initial Inspection and Diagnostic Overview

It is important to get an accurate description of the complaint before any diagnosis can be performed. Ask questions as to whether it occurs hot or cold, during shifting, driving at a particular speed or in a particular gear. If possible, have the customer demonstrate the concern.

COLD TRANSMISSION
- Drive the vehicle in all gears (1-5 and REVERSE gears).
- Evaluate the noise in NEUTRAL. Check if there are any noise changes in a particular gear (i.e., 4th gear). In 4th gear, the countershaft cluster gear is not under load.
Check if the noise increases when the transmission is warmed up.
- See if the noise is related to engine speed, road speed, or gear selection.

WARM TRANSMISSION
- Check all gears plus REVERSE gear and make note of any noise changes in a particular gear
- In REVERSE gear, the fifth/reverse synchronizer sleeve locks the REVERSE gear to the countershaft. The input gear drives the countershaft. The countershaft reverse gear drives the reverse idler gear. The reverse idler gear drives the reverse gear on the output shaft. The output shaft is driven in the opposite direction of the input shaft at a ratio of 3.91:1.
- Check noise in NEUTRAL while parked. Check if the noise disappears at a certain engine RPM or with the clutch pedal depressed.
- Drive in the gear in which the noise is most noticeable. Press in the clutch pedal and leave the gear engaged. If the noise changes or disappears, the noise may be amplified by the vibration of the engine.
- Drive under the same condition again. Press the clutch pedal in and shift into NEUTRAL. Release the clutch pedal while the vehicle is coasting down the road. Evaluate the noise as the rear axle assembly turns the mainshaft.