GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2009 🢒 TopKick C-Series (Conventional) C6/C7/C8 🢒 Transmission 🢒 Manual Transmission - Medium Duty 🢒 Transmission Jumps Out of Gear

Diagnostic Aids

If the transmission jumps out of gear during deceleration, inspect the components that may allow for the gears or shafts to tip. If the gears or shafts tip, the synchronizer sleeve can disengage from the selector teeth on the speed gear. If the transmission jumps out of gear during acceleration, inspect the components that may not allow full engagement of the synchronizer sleeve to the selector teeth on the speed gear. Insufficient engagement of the selector teeth under torque may cause the transmission to jump out of gear.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. A static shift test is performed by shifting into all gear positions with the engine not operating. While performing the test, slowly move the shift lever. Feel for proper movement of the shift controls and transmission internal shift components.

    2.

  2. A dynamic shift test is performed by shifting into all gear positions with the engine operating. Test for the correct mesh of the synchronizers sleeve and the speed gear selector teeth. Move the shift lever, and feel for the synchronizer sleeve to release form the gear, and then let up on the clutch pedal. Depress the clutch pedal and move the shift lever to engage the gear again, to ensure full travel of the shift components.

    3.

  3. This step inspects for worn or damaged transmission or engine mounts. Loose mounts may cause a shock on the transmission, allowing for gear disengagement.

    4.

  4. This step inspects for the misalignment of the clutch to transmission. Misalignment may put a bind on the input shaft, allowing for the input shaft or the mainshaft to tip.

    5.

  5. This step inspects the pilot bearing and the pilot bearing journal on the input shaft. A worn pilot bearing or input shaft may allow the input shaft to tip causing gear disengagement.

Step

Action

Yes

No

DEFINITION: Gear disengagement occurs during acceleration or deceleration.

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 symptom operations and perform the necessary inspections?

Go to Step 2

Go to Symptoms - Manual Transmission

2

  1. Perform a static shift test.
  2. Test for the following:
    3. • Blockage preventing full shift lever movement
    • Excessive movement in the shift lever
    • Excessive movement in the shift control and the shift control linkage
    • Correct shift cable adjustment

Did you find and repair the condition?

Go to Step 10

Go to Step 3

3

  1. Perform a dynamic shift test on the transmission.
  2. Test for the following:
    3. • Synchronizer sleeve or sliding clutch engagement to the speed gear selector teeth
    • Detent plungers engaging in the shift rails

Did the transmission shift completely into all gears?

Go to Step 4

Go to Step 7

4

Inspect the engine and/or transmission mounts. Refer to Engine Mount Inspection .

Did you find and repair the condition?

Go to Step 10

Go to Step 5

5

Inspect the clutch housing for loose bolts or misalignment.

Are there any loose bolts or misalignment?

Go to Step 6

Go to Step 7

6

Tighten any loose housing bolts and/or align the housing . Refer to Clutch Assembly Replacement .

Did you find and repair the condition?

Go to Step 10

Go to Step 7

7

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

Did you find and repair the condition?

Go to Step 10

Go to Step 8

8

  1. Remove the transmission. Refer to Transmission Replacement .
  2. Remove the clutch assembly. Refer to Clutch Assembly Replacement .
  3. Inspect the pilot bearing for being faulty.
  4. Inspect the input shaft for excessive wear at the pilot bearing.

Did you find and repair the condition?

Go to Step 10

Go to Step 9

9
  1. Disassemble the transmission. Refer to the transmission manufacturer repair manual.
  2. Inspect the following components for wear or damage:
    3. • The synchronizer sleeve and speed gear selector teeth
    • The sliding clutch teeth
    • The mainshaft to input shaft bearing and journals
    • The speed gear bearings and journals
    • The speed gear axial clearance
    • The mainshaft center and rear bearings

Did you find and repair the condition?

Go to Step 10

Go to Diagnostic Aids

10

Operate the system in order to verify the repair.

Did you correct the condition?

System OK

Go to Step 1