GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Isuzu 🢒 2007 🢒 Isuzu MD F-Series 🢒 Transmission/Transaxle 🢒 Manual Transmission - Medium Duty 🢒 Transmission Gear Clash When Shifting Gears

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.

  1. 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.

    2.

  2. 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 how the shift lever and the shift cable movement is felt. 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 control linkage or a shift cable that is not adjusted properly may prevent the shift forks from fully engaging the synchronizer.

    3.

  3. 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, if equipped, 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 engage that gear again. 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 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

Go to Symptoms - Manual Transmission

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 .

Does the clutch operate properly?

Go to Step 5

Go to Step 4

4

Repair the clutch system. Refer to Symptoms - 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 the transmission manufacturer repair manual.

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 15

7

  1. Perform a static shift test on the transmission.
  2. Test for the following:
    3. • Blockage preventing full shift lever movement
    • Excessive movement in the shift control
    • Binding in the shift cables
    • Correct shift cable adjustment
    • Detent plungers or shift rails binding

Did the transmission shift smoothly into the gear that is clashing?

Go to Step 13

Go to Step 8

8

Inspect the shift control and the shift control linkage for excessive movement and wear.

Is there excessive movement in the shift control or the shift control linkage?

Go to Step 9

Go to Step 10

9

Repair or replace the faulty components in the shift control or shift control linkage. Refer to the transmission manufacturer repair manual.

Did you find and repair the condition?

Go to Step 15

Go to Step 10

10

Inspect the shift cable for the proper adjustment. Refer to Shift Cable Adjustment .

Is the shift cable adjusted properly?

Go to Step 12

Go to Step 11

11

Adjust or repair the shift control cable. Refer to Shift Cable Adjustment .

Did you find and repair the condition?

Go to Step 15

Go to Step 12

12

Remove the shift cover and inspect for damage or worn components. Refer to the transmission manufacturer repair manual.

Did you find and repair the condition?

Go to Step 15

Go to Step 14

13

  1. Perform a dynamic shift test on the transmission.
  2. Test for the following:
    3. • Detent plungers or shift rails binding
    • Synchronizer sleeve binding
    • Sliding clutch binding
    • Gear clashing in more than the suspected gear

Is the transmission hard to shift into all gears?

Go to Transmission Shifts Hard

Go to Step 14

14
  1. Disassemble the transmission. Refer to the transmission manufacturer repair manual.
  2. Inspect the following transmission components for the suspect gear that is clashing.
    3. • Excessive synchronizer blocking ring to gear clearance
    • Synchronizer sleeve to hub clearance excessive
    • Excessive axial clearance in the speed gear
    • Mainshaft to speed gear bearing or journal worn
    • Shift fork worn or damaged
    • Internal shift control worn or damaged
    • Mainshaft bearing worn or damaged
    • Input gear bearing or pilot bearing worn

Did you find and repair the condition?

Go to Step 15

Go to Diagnostic Aids

15

Operate the system and verify the repair.

Did you correct the condition?

System OK

Go to Step 1