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Home >> GMC >> 2006 >> Sierra 1500 HD, RWD >> Repair and Diagnosis >> External Pages >> Different variant/trim >> Section 20 (Manual Transmission - NV 3500 - Service) >> Diagnostic Information and Procedures >> Transmission Gear Clash When Shifting Gears >> Test Description

Test Description

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The numbers below refer to step numbers on diagnostic table.

  1. 2:  This step tests for proper releasing of clutch. If clutch reserve is not proper, mainshaft gears may still be turning causing gear clashing.
  2. 5:  This step inspects for proper transmission fluid. A special fluid is required for correct lubrication of synchronizers.
  3. 7:  A static shift test is performed by shifting into all of gear positions with engine not operating. While performing test, you should note how shift lever movement is felt. Also, while shifting from one gear to another, feel for binding in shift rails. You should be able to feel detent plungers operating when coming out of a gear and going into a gear. Excessive play in gear shift lever may prevent shift forks from fully engaging synchronizer.
  4. 9:  A dynamic shift test is performed by shifting into all of gear positions with engine operating. Test for correct mesh of synchronizers, and for clutch releasing correctly. Move shift lever and feel for synchronizer sleeve to just release from gear, then let up on clutch pedal. Depress clutch pedal and move shift lever to re-engage that gear. If it shifts back into gear without clashing, clutch is releasing correctly and synchronizer is working. If clashing occurs, test on another gear. If all gears clash, clutch is not releasing correctly.
Transmission Gear Clash When Shifting Gears

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.
1 Did you review the Symptoms - Manual Transmission, 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 Transmission Fluid Replacement .
Is the transmission fluid level correct and at the proper level?		 Go to Step 7  Go to Step 6 
6 Fill the transmission fluid to the correct level, or change the transmission fluid if it is not the correct type. Refer to Transmission Fluid Replacement .
Does the transmission still have gear clash?		 Go to Step 7  Go to Step 11 
7
  1. Perform a static shift test on the transmission.
  2. Test for the following:
    • Blockage preventing full shift lever movement
    • Excessive movement in the shift lever
    • Binding in the shift lever
    • Detent plungers or shift rails binding
Did the transmission shift smoothly into the gear that is clashing?		 Go to Step 9  Go to Step 8 
8 Remove the shift lever and inspect for damage or worn components. Refer to Shift Lever Assembly Replacement .
Did you find and repair the condition?		 Go to Step 11  Go to Step 9 
9
  1. Perform a dynamic shift test on the transmission.
  2. Test for the following:
    • Detent plungers or shift rails binding
    • Synchronizer sleeve 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 10 
10
  1. Disassemble the transmission. Refer to TRANSMISSION DISASSEMBLE .
  2. Inspect the following transmission components for the gear that is clashing:
    • 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 11  Go to Diagnostic Aids 
11 Operate the system and verify the repair.
Did you correct the condition?		 System OK Go to Step 1 
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