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Home >> GMC >> 2006 >> Sierra 1500 HD, RWD >> Repair and Diagnosis >> External Pages >> Different variant/trim >> Section 56 (Manual Transmission - NV 3500 - Overhaul) >> Repair Instructions >> Mainshaft and Synchronizers >> Notes

Mainshaft and Synchronizers: Notes

WARNING: This page is about a different variant/trim than selected.
  1. Clean all the parts in a suitable cleaning solvent. Air dry all the parts.
    2. IMPORTANT: Do not spin the bearings without a lubricant.
  2. Lubricate the mainshaft bearings with Synchromesh Transmission Fluid GM P/N 12345349 (Canadian P/N 10953465) or equivalent.
  3. Inspect the bearings for rough rotation.
  4. Inspect the mainshaft gears for the following conditions:
    • Cracks
    • Nicks
    • Chipped gear teeth
    • High spots, small-shiny spots on the gear teeth mating surface, that could cause gear noise
  5. Inspect related gear surfaces like thrust faces and bearing surface diameters.
  6. Inspect the synchronizer sleeves for a sliding fit on the synchronizer hubs. The synchronizer hubs must have a force fit on the mainshaft splines.
  7. Replace a synchronizer hub that does not require a force fit on the mainshaft splines.
  8. Inspect the synchronizer springs and the keys for damage.
  9. Inspect the synchronizer rings for excess wear.
  10. Inspect the synchronizer clutching teeth for the following conditions:
    • Scuffs
    • Nicks
    • Burrs
    • Damage
  11. Measure the gap between the vertical faces of the blocking ring teeth and the synchronizer clutch gear as follows:
    1. Assemble the correct blocking ring with the correct speed gear.
    2. The blocking ring must be fully seated on the gear.
    3. If dual cone, install both cones. Ensure the top edge of the friction cone is parallel to the gear face.
    4. Use a feeler gauge to measure the gear gap.
      • 1st gear 1.45-2.38 mm (0.057-0.094 in)
      • 2nd gear 1.42-2.40 mm (0.055-0.094 in)
      • Reverse, 3rd, 4th, and 5th gear 1.44-2.12 mm (0.057-0.083 in)
      Fig 1: Measuring Gap Between Blocking Ring & Synchronizer Clutch Gear
      GM38591Courtesy of GENERAL MOTORS CORP.
  12. Inspect the mainshaft drive gear clutching cones for synchronizer ring metal transfer.
  13. Inspect all the gear teeth for excess wear.
  14. Remove nicks and burrs with a soft stone or a crocus cloth.
  15. Replace any components that are bent or show signs of excessive wear. Inspect the mating parts.
  16. Inspect the bearings and the bearing surfaces for the following conditions:
    • Nicks
    • Burrs
    • Bent cages
    • Wear
    • Overheating
    • Scoring
    • Pitted condition
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