Evaluation of Noises Under Different Load Conditions

It is important to get an accurate description of the complaint from the customer. 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 demostrate the concern.
Cold Transmission

^ Drive the truck 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 is not under load.

^ Check if the noise increases when the transmission is warming 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.
^ 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 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 while the truck is coasting down the road. Evaluate the noise, as the drive axle turns the transmission mainshaft.

ADDITIONAL TESTING FOR 4X4 TRUCKS (Non-Electronic Shift)

^ Check for any noise change when shifting the transfer case between 4x2, 4 high, 4 low or into neutral.

^ With the truck at a complete stop and the transfer case in neutral, shift through all the the gears and evaluate noise at different engine RPM. Check for any noises in neutral at different engine RPM.
Once you have identified the area that the noise is coming from, refer to the troubleshooting guide for concern resolution.

NOTE: THE LATEST LIGHT TRUCK SHOP MANUAL, TRANSMISSION SECTION HAS UPDATED SERVICE INFORMATION AND DIAGNOSTIC PROCEDURES THAT APPLY 1987 AND LATER MODEL YEAR TRUCKS.