Manual Transmission Diagnosis for Chevrolet

Transmission components
Transmission components

This article pertains to the Chevrolet transmissions used in the 60s-80s. It may apply to different types for its diagnosis of problems.

Many problems are due to worn linkages, swivels, cushions. Make sure there is free clutch pedal travel and nothing seems to interfere with clutch operation. To test for clutch spin down, run the engine in neutral and clutch engaged. Disengage the clutch, wait nine seconds and shift into reverse. No grinding noise should be heard. If there is, then the clutch in incorrectly set or there is an internal problem.

Hard shifting occurs when the effort is excessive yet the tranny goes into the gear. If the engine is off and shifting is hard, the synchronizer sleeve and hubs should be checked for being too tight. If this is not the case, replace the synchronizer assembly. If the gears do not engage, a double bump is felt. In this case, the blocker ring be be stuck or sticking to the synchronizer gear cone. Visually, it looks brassy and should look silver. Use 400 grit sand paper to return it to the silver color. Replace the blocker rings if the thread is damaged.

Gear clash occurs when you hear a sound when the sleeve and gear chamfers contact each other in a unsynchronized mode creating a grating or loud buzzing sound and vibration is felt. If this occurs, check the sleeves for chipping and burrs, if damaged, the synchronizer assemblies and blocker rings need to be replaced. If there is any chipping, replace the synchronizer.

Gear slipping is usually the cause of any of the following:  bad adjustment, oil soaked driven disc, worn facing from disc, warped pressure plate or flywheel, weak diaphragm. If the tranny is noisy, check for insufficient lubricant, worn bearings or damaged main drive gear shaft bearings or countergear anti-lash plate.

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