GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2001 🢒 Sonoma Pickup - 2WD 🢒 Transmission/Transaxle 🢒 Manual Transmission - NV 1500 🢒 Synchronizers Cleaning and Inspection

    Object Number: 648209 Size: SH

    Important: When you service the synchronizers, keep them in the order that they are removed.

  1. Clean all the parts in a suitable cleaning solvent. Air dry all the parts.
  2. Inspect the 1st/2nd and the 3rd/4th synchronizer hubs for a loose fit on the mainshaft.
  3. Replace synchronizer hubs that are loose on the mainshaft.
  4. Inspect the synchronizer hub for wear on the external splines. A stepped effect on the teeth due to wear may cause shift problems.
  5. Replace a worn hub.
  6. Correct the cause such as but not limited to the following:
    7. • Engine related vibrations
    • Driving at a low speed in a high gear
    • Defective vibration damper or crankshaft
  7. Inspect the inserts for wear or for damage.
  8. Inspect the springs for distortion.
  9. Inspect the balls for wear or for flat spots.

    10. Object Number: 648210 Size: SH
  10. Inspect the synchronizer sleeve teeth (1) for the following, which may cause shift problems:
    11. • Grated teeth
    • Chipped off teeth
    • Blunted teeth
  11. Inspect the synchronizer sleeve detent stops (2) for wear or being chipped off.
  12. Replace the synchronizer assembly if the teeth or stops show the above conditions.

    13. Object Number: 648207 Size: SH
  13. Inspect the synchronizer blocker rings for worn away grooves.
  14. Replace the blocker ring assembly if the blocker ring grooves are worn away.
  15. If dual cone, inspect the center ring for worn or damaged friction material.
  16. Replace the synchronizer assembly if the center cone is worn or damaged.

    17. Object Number: 648208 Size: SH
  17. Inspect the synchronizer blocker rings for worn shift teeth.
  18. Inspect the center ring for being warped or damaged.
  19. Inspect the inner ring for worn grooves.
  20. Replace the synchronizer ring assembly for any of the above conditions.

    21. Object Number: 648192 Size: SH
  21. Measure the blocker ring to gear clearance.
    22. 21.1. Assemble the correct blocker ring to the correct gear.
    21.2. If dual cone, install both cones. Ensure the top edge of the friction cone is parallel to the gear.
    21.3. Apply pressure to the blocker ring to fully seat the ring.
    21.4. Using a feeler gage measure between the blocker ring teeth and the teeth on the gear.
       • The measured values for the 1st gear to synchronizer clearance are 1.070-1.870 mm (0.042-0.074 in).
       • The measured values for the 2nd gear to synchronizer clearance are 1.07-2.12 mm (0.074-0.083 in).
       • The measured values for the 3rd gear to synchronizer clearance are 0.925-1.585 mm (0.036-0.062 in).
       • The measured values for the 4th gear to synchronizer clearance are 0.975-1.535 mm (0.038-0.060 in).
       • The measured values for the 5th gear to synchronizer clearance are 0.950-1.560 mm (0.037-0.061 in).
       • The measured values for the reverse gear to synchronizer clearance are 1.170-1.720 mm (0.0426-0.068 in).
  22. If using a NEW blocker ring and the standard clearance can not be obtained replace the gear.