Synchronizers Cleaning and Inspection

WARNING: This page is about a different variant/trim than selected.

IMPORTANT: When you service the synchronizers, retain them in the same order that they are removed. Mark the parts to ensure the correct position for inspection and assembly.

Clean all the parts in a suitable cleaning solvent and air dry.
Inspect the 2nd/3rd, 4th/5th synchronizer hubs for a force fit on the mainshaft.
The 6th gear synchronizer hub and the 1st/reverse gear synchronizer hub are slip fit.
Replace synchronizer hubs that do not require a force fit.
Inspect the synchronizer hub for wear on the external splines. A stepped effect on the teeth, due to wear, may cause shift conditions.

Fig 1: Identifying Stepped Effect On Synchronizer Teeth
Courtesy of GENERAL MOTORS CORP.
Replace a worn hub.
Correct the cause, such as, but not limited to the following conditions:
- Engine related vibrations
- Driving at a low speed in a high gear
- Defective vibration damper or crankshaft
- Incorrectly set injector pump
Inspect the synchronizer sleeve teeth (1) for the following, which may cause shift conditions:

Fig 2: Inspecting Synchronizer Sleeve Teeth
Courtesy of GENERAL MOTORS CORP.
- Grated teeth
- Chipped off teeth
- Blunted teeth
Inspect the synchronizer sleeve detent stops (2) for wear or being chipped off.
Replace the synchronizer assembly if the teeth or stops show the above conditions.
Inspect the synchronizer blocker rings for worn away grooves.

Fig 3: Inspecting Synchronizer Blocker Rings For Worn Away Grooves
Courtesy of GENERAL MOTORS CORP.
Replace the blocker ring assembly if the blocker ring grooves are worn away.
Inspect the synchronizer blocker rings for worn shift teeth.

Fig 4: Inspecting Synchronizer Blocker Rings For Wear Or Damage
Courtesy of GENERAL MOTORS CORP.
Inspect the middle ring for being warped or damaged.
Inspect the outer ring for worn grooves.
Replace the synchronizer assembly if any of the above conditions are found.
Measure the blocker ring to gear clearance.

Fig 5: Measuring Blocker Ring To Gear Clearance
Courtesy of GENERAL MOTORS CORP.
1. Assemble the correct blocker ring to the correct gear.
2. Apply pressure to the blocker ring to fully seat the ring.
3. Using a feeler gage, measure between the blocker ring teeth and the teeth on the gear.
  - Synchronizer Reserve - New Gear, New Ring 2nd/3rd, Dual Cone, clearance between the blocker ring and the gear is 1.5-0.1.85 mm (0.059-0.073 in).
  - Synchronizer Reserve - New Gear, New Ring 4th, 5th, 6th, 1st, and reverse between the blocker ring and the gear is 1.4-1.7 mm (0.055-0.067 in).
Gear clash occurs around reserve 1.0 mm (0.039 in) or less.
If using a NEW blocker ring and the standard clearance can not be obtained, replace the gear.
Inspect the pressure pieces for wear or damage.
Inspect the springs for distortion.