Diagnostic Aids
Gear clashing may be caused by shifting at too high of an engine RPM or by rushing the shift. If gear clashing occurs in more than one gear, the clutch may not be releasing properly for proper synchronizer operation.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step tests for the proper releasing of the clutch. If the clutch reserve is not proper, the mainshaft gears may still be turning causing the gear clashing. If equipped with a clutch brake, ensure the clutch brake is operating properly.
-
A static shift test is performed by shifting into all of the gear positions with the engine not operating. While performing the test, you should note the shift lever movement. Also, while shifting from one gear to the other, feel for binding in the shift rails. You should be able to feel the detent plungers operating when coming out of a gear and going into a gear. Excessive play in the shift lever or a shift control housing may prevent the shift forks from fully engaging the synchronizer, if equipped.
-
A dynamic shift test is performed by shifting into all of the gear positions with the engine operating. Test for the correct mesh of the synchronizers and for the clutch releasing correctly. Move the shift lever and feel for the synchronizer sleeve to just release from the gear then let up on the clutch pedal. Depress the clutch pedal and move the shift lever to re-engage that gear. If it shifts back into the gear without clashing, the clutch is releasing correctly and the synchronizer is working. If clashing occurs, test on another gear. If all gears clash, the clutch is not releasing correctly.
Step | Action | Yes | No | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
DEFINITION: Noise from the transmission when shifting gears. A grinding or grating sound when the synchronizer sleeve or the sliding clutch gear is engaging with the selector teeth on the speed gear. A suspected internal transmission condition, if the noise only occurs in one gear. If the transmission is equipped with an air shift control, refer to the transmission manufacturer repair manual for the correct diagnosis and repair. | |||||||||||||||
1 | Did you review the manual transmission symptoms and perform the necessary inspections? | Go to Step 2 | |||||||||||||
With the engine operating, does the transmission shift from neutral to any gear without the vehicle lurching or gear clashing? | Go to Step 5 | Go to Step 3 | |||||||||||||
3 | Inspect for proper clutch operation. Refer to Clutch System Description and Operation in Clutch. Does the clutch operate properly? | Go to Step 5 | Go to Step 4 | ||||||||||||
4 | Repair the clutch system. Refer to Symptoms - Clutch in Clutch. Did you find and repair the condition? | Go to Step 11 | Go to Step 5 | ||||||||||||
5 | Inspect for the correct transmission fluid level and the proper fluid. Refer to Transmission Fluid Check . Is the transmission fluid level correct and at the proper level? | Go to Step 7 | Go to Step 6 | ||||||||||||
6 | Fill the transmission to the correct level or change the fluid if it is the incorrect type. Refer to Lubrication Specifications . Does the transmission still have gear clash? | Go to Step 7 | Go to Step 12 | ||||||||||||
Did the transmission shift smoothly into the gear that is clashing? | Go to Step 10 | Go to Step 8 | |||||||||||||
8 |
Did you find and repair the condition? | Go to Step 12 | Go to Step 9 | ||||||||||||
9 | Remove the shift control housing. Refer to the transmission manufacturer service manual. Did you find and repair the condition? | Go to Step 12 | Go to Step 10 | ||||||||||||
Is the transmission hard to shift into all gears? | Go to Transmission Shifts Hard | Go to Step 11 | |||||||||||||
11 |
Did you find and repair the condition? | Go to Step 12 | Go to Diagnostic Aids | ||||||||||||
12 | Operate the system and verify the repair. Did you correct the condition? | System OK | Go to Step 1 | ||||||||||||
