GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Isuzu 🢒 1999 🢒 S/T Isuzu - 2WD 🢒 Transmission/Transaxle 🢒 Manual Transmission - NV 3500 🢒 Mainshaft and Synchronizers
  1. Clean all the parts in a suitable solvent. Air dry all the parts.

    2. Important: Do not spin the bearings without a lubricant.

  2. Lubricate the mainshaft bearings with the proper transmission lubricant.
  3. Check the bearings for rough rotation.
  4. Inspect the mainshaft gears for the following conditions:
    5. • 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:
    11. • Scuffs
    • Nicks
    • Burrs
    • Damage
  11. Inspect the mainshaft drive gear clutching cones for synchronizer ring metal transfer.
  12. Inspect all the gear teeth for excess wear.
  13. Remove nicks and burrs with a soft stone or a crocus cloth.
  14. Replace any components that are bent or show signs of excessive wear. Inspect the mating parts.
  15. Inspect the bearings and the bearing surfaces for the following conditions:
    16. • Nicks
    • Burrs
    • Bent cages
    • Wear
    • Overheating
    • Scoring
    • Pitted condition

Mainshaft and Synchronizers Disassemble


    Object Number: 4735 Size: SH
  1. Remove the 5th speed gear drag seal.
  2. Remove the reverse speed gear drag seal.
  3. Remove the reverse speed gear and reverse speed gear needle bearing.

    4. Object Number: 7906 Size: SH
  4. Remove the 5th/Reverse speed gear synchronizer.
  5. Remove the mainshaft snap ring.

    6. Object Number: 4739 Size: SH
  6. Remove the 5th speed gear (3), synchronizer ring (2), and 5th speed gear needle bearing (1).

    7. Object Number: 4811 Size: SH
  7. Remove the 1st speed gear needle bearing assembly.

    8. Object Number: 4740 Size: SH
  8. Remove the synchronizer cone, blocker ring, reaction cone, synchronizer interim ring, and 1st speed gear.
  9. Remove the 1st/2nd speed gear synchronizer assembly and both synchronizer rings.

    10. Object Number: 7907 Size: SH
  10. Remove the mainshaft snap ring.

    11. Object Number: 4815 Size: SH
  11. Remove the interim ring, reaction cone, blocker ring, and synchronizer cone.

    12. Object Number: 4743 Size: SH
  12. Remove the 2nd speed gear (1) and the 2nd speed gear needle bearing (2).

    13. Object Number: 4812 Size: SH
  13. Remove the 2-piece thrust washer and 2nd speed gear.

    14. Object Number: 4745 Size: SH
  14. Remove the synchronizer ring, 3rd speed gear, and needle bearing.

    15. Object Number: 4746 Size: SH
  15. Remove the 3rd/4th speed gear synchronizer assembly and both synchronizer rings.

    16. Object Number: 4808 Size: SH
  16. Remove the mainshaft snap ring.
  17. Clean all the parts in a suitable solvent. Air dry all the parts.
  18. Check the bearings for rough rotation.
  19. Inspect the mainshaft gears for the following conditions:
    20. • Cracks
    • Nicks
    • Chipped gear teeth
    • High spots (small-shiny spots on the gear teeth mating surface) that could cause gear noise
  20. Inspect related gear surfaces like thrust faces and bearing surface diameters.
  21. Inspect the synchronizer sleeves for a sliding fit on the synchronizer hubs. The synchronizer hubs must have a force fit on the mainshaft splines.
  22. Replace a synchronizer hub that does not require a force fit on the mainshaft splines.
  23. Inspect the synchronizer springs and the keys for damage.
  24. Inspect the synchronizer rings for excess wear.
  25. Inspect the synchronizer clutching teeth for the following conditions:
    26. • Scuffs
    • Nicks
    • Burrs
    • Damage
  26. Inspect the mainshaft drive gear clutching cones for synchronizer ring metal transfer.
  27. Inspect all the gear teeth for excess wear.
  28. Remove nicks and burrs with a soft stone or a crocus cloth.
  29. Replace any components that are bent or show signs of excessive wear. Inspect the mating parts.
  30. Inspect the bearings and the bearing surfaces for the following conditions:
    31. • Nicks
    • Burrs
    • Bent cages
    • Wear
    • Overheating
    • Scoring
    • Pitted condition

Mainshaft and Synchronizers Assemble, Rear Wheel Drive

Mainshaft Assembly

Tools Required

    • Hydraulic Press
    • J 36183 Input Shaft Press Tube with Cap
    • J 36184 Adapter Press Tube Reducer
    • J 39924-1 Reverse Drag Seal Installer
    • J 39924-2 5th Speed Gear Drag Seal Installer

    Important: Some components require an assembly lubricant. Use TRANSJEL or equivalent.


    Object Number: 4736 Size: SH
  1. Install the 5th speed gear drag seal. Use J 39924-2 and J 36183 .

    2. Object Number: 4737 Size: SH
  2. Install the reverse speed gear drag seal. Use J 39924-1 .

    3. Object Number: 4735 Size: SH
  3. Install the following components:
    4. 3.1. The reverse speed gear needle bearing assembly
    3.2. The reverse speed gear

    Object Number: 4738 Size: SH
  4. Install the 5th/Reverse speed gear synchronizer.
    5. 4.1. Check the scribe marks for correct positions.
    4.2. Position the spiral lock ring towards the reverse speed gear.
    4.3. Manually align and engage the splines.
    4.4. Use J 36183 and J 36184 .
    4.5. Press the synchronizer until seated.
    4.6. Remove all the metal shavings.

    Object Number: 7906 Size: SH
  5. Install a new mainshaft snap ring.

    6. Object Number: 4739 Size: SH
  6. Install the following components:
    7. 6.1. The 5th speed gear needle bearing assembly
    6.2. The synchronizer ring
    6.3. The 5th speed gear

    Object Number: 4811 Size: SH
  7. Install the 1st speed gear needle bearing assembly

    8. Important: The groove on the outside of the synchronizer sleeve must go towards the 2nd speed gear. This prevents gear clash during 1st and 2nd speed gear shifts. The teeth of the sleeve have different angles.


    Object Number: 4740 Size: SH
  8. Install the following components:
    9. 8.1. The 1st speed gear
    8.2. The synchronizer interim ring with the teeth up
    8.3. The reactor cone with the flat side towards 1st gear
    8.4. The blocker ring with the teeth down
    8.5. The synchronizer cone with the flat side down

    Object Number: 4810 Size: SH
  9. Check the 1st/2nd speed gear synchronizer assembly scribe marks for correct positions.

    10. Object Number: 4741 Size: SH
  10. Install the 1st/2nd speed gear synchronizer assembly with both synchronizer rings.
    11. 10.1. Manually align and engage the splines.
    10.2. Use J 36183 , J 36184 and a hydraulic press.
    10.3. Start the press operation.
             10.3.1. Stop pressing before the tangs engage.
             10.3.2. Lift and rotate the gear.
             10.3.3. Engage the synchronizer ring.
    10.4. Press the synchronizer until seated.
    10.5. Remove all the metal shavings.

    Object Number: 4815 Size: SH
  11. Install the following components:
    12. 11.1. The synchronizer cone with the flat up
    11.2. The blocker ring with the tangs up
    11.3. The reaction cone with the wide flat portion up
    11.4. The interim ring

    Object Number: 7907 Size: SH
  12. Install a new mainshaft snap ring.

    13. Object Number: 4743 Size: SH
  13. Install the following components:
    14. 13.1. The 2nd speed gear needle bearing assembly
    13.2. The 2nd speed gear

    Ensure that the bearing cage is together. Ensure that the synchronizer ring gear teeth are toward 1st gear.


    Object Number: 4812 Size: SH
  14. Install the following components:
    15. 14.1. The 2nd speed gear 2-piece thrust washer

    Ensure that the dots are facing up.

    14.2. The retainer ring

    Ensure that the retainer ring is installed around the washer.


    Object Number: 4745 Size: SH
  15. Install the following components:
    16. 15.1. The 3rd speed gear needle bearing assembly
    15.2. The 3rd speed gear
    15.3. The synchronizer ring

    Object Number: 4810 Size: SH
  16. Check the 3rd/4th speed gear synchronizer assembly scribe marks for correct positions.

    17. Object Number: 4746 Size: SH
  17. Install the 3rd/4th speed gear synchronizer assembly with both synchronizer rings. Ensure that the groove in the synchronizer ring faces upward.
    18. 17.1. Manually align and engage the splines.
    17.2. Use J 36183 , J 36184 , and a hydraulic press.
    17.3. Start the press operation
             17.3.1. Stop pressing before the tangs engage.
             17.3.2. Lift and rotate the gear.
             17.3.3. Engage the synchronizer ring.
    17.4. Press the synchronizer until seated.
    17.5. Remove all the metal shavings.

    Object Number: 4808 Size: SH
  18. Install a new mainshaft snap ring.

Mainshaft and Synchronizers Assemble, Four Wheel Drive

Mainshaft Assembly

Tools Required

    • Hydraulic Press
    • J 36183 Input Shaft Press Tube with Cap
    • J 36184 Adapter Press Tube Reducer
    • J 39924-1 Reverse Drag Seal Installer
    • J 39924-2 5th Speed Gear Drag Seal Installer

    Important: Some components require an assembly lubricant. Use TRANSJEL or equivalent.


    Object Number: 4736 Size: SH
  1. Install the 5th speed gear drag seal. Use J 39924-2 and J 36183 .

    2. Object Number: 4737 Size: SH
  2. Install the reverse speed gear drag seal. Use J 39924-1 .

    3. Object Number: 4735 Size: SH
  3. Install the following components:
    4. 3.1. The reverse speed gear needle bearing assembly.
    3.2. The reverse speed gear.

    Object Number: 4738 Size: SH
  4. Install the 5th/Reverse speed gear synchronizer.
    5. 4.1. Check the scribe marks for the correct positions.
    4.2. Position the spiral lock ring towards the reverse speed gear.
    4.3. Manually align and engage the splines.
    4.4. Use J 36183 and J 36184 .
    4.5. Press the synchronizer until seated.
    4.6. Remove all the metal shavings.

    Object Number: 7906 Size: SH
  5. Install a new mainshaft snap ring.

    6. Object Number: 4739 Size: SH
  6. Install the following components:
    7. 6.1. The 5th speed gear needle bearing assembly
    6.2. The synchronizer ring
    6.3. The 5th speed gear

    Object Number: 4811 Size: SH
  7. Install the 1st speed gear needle bearing assembly

    8. Important: The groove on the outside of the synchronizer sleeve must go towards the 2nd speed gear. This prevents gear clash during 1st and 2nd speed gear shifts. The teeth of the sleeve have different angles.


    Object Number: 4740 Size: SH
  8. Install the following components:
    9. 8.1. The 1st speed gear
    8.2. The synchronizer interim ring
    8.3. The reaction cone
    8.4. The blocker ring
    8.5. The synchronizer cone

    Object Number: 4810 Size: SH
  9. Check the 1st / 2nd speed gear synchronizer assembly scribe marks for correct positions.

    10. Object Number: 4741 Size: SH
  10. Install the 1st/2nd speed gear synchronizer assembly with both synchronizer rings:
    11. 10.1. Manually align and engage the splines.
    10.2. Use J 36183 and J 36184 and a hydraulic press.
    10.3. Start the press operation.
       • Stop pressing before the tangs engage.
       • Lift and rotate the gear.
       • Engage the synchronizer ring.
    10.4. Press the synchronizer until seated.
    10.5. Remove all the metal shavings.

    Object Number: 7907 Size: SH
  11. Install a new mainshaft snap ring.

    12. Object Number: 4815 Size: SH
  12. Install the following components:
    13. 12.1. The synchronizer cone
    12.2. The blocker ring
    12.3. The reaction cone
    12.4. The interim ring

    Object Number: 4743 Size: SH
  13. Install the following components:
    14. 13.1. The 2nd speed gear needle bearing assembly
    13.2. The 2nd speed gear

    Make sure the bearing cage is together.


    Object Number: 4812 Size: SH
  14. Install the following components:
    15. 14.1. The 2nd speed gear 2-piece thrust washer (Install the 2-piece thrust washers with the locating dots facing up.)
    14.2. The retainer ring

    Object Number: 4745 Size: SH
  15. Install the following components:
    16. 15.1. The 3rd speed gear needle bearing assembly
    15.2. The 3rd speed gear
    15.3. The synchronizer ring

    Object Number: 4810 Size: SH
  16. Check the 3rd/4th speed gear synchronizer assembly scribe marks for correct positions.

    17. Object Number: 4746 Size: SH
  17. Install the 3rd/4th speed gear synchronizer assembly with both synchronizer rings.
    18. 17.1. Manually align and engage the splines.
    17.2. Use tools J 36183 and J 36184 , and a hydraulic press.
    17.3. Start the press operation.
             17.3.1. Stop pressing before the tangs engage.
             17.3.2. Lift and rotate the gear.
             17.3.3. Engage the synchronizer ring.
    17.4. Press the synchronizer until seated.
    17.5. Remove all the metal shavings.

    Object Number: 4808 Size: SH
  18. Install a new mainshaft snap ring.