Synchronizer Ring Tips

Overview

This guide summarizes key points on diagnosing and preventing stuck synchronizer rings in manual transmissions. It explains why the issue occurs, how to identify it, and the correct steps to fix and prevent it during transmission assembly or shipping.

1. Common Cause: Stuck Synchronizer Rings

• Symptom: Transmission appears stuck in two gears at once.
• Main Cause: Synchronizer ring becomes jammed against the gear during shipping or from being shifted while dry.
• Root Problems:
  • Transmission shipped or stored completely dry.
  • Builder or buyer bench-shifted a dry transmission.
  • Microscopic machining threads on new gears cause rings to screw onto the cone and stick.

2. Gear Surface Finish Differences

• Used Gear:
  • Burnished, smooth finish.
  • Allows the synchronizer ring to grip and release freely.
• New Gear:
  • Hard-turned surface with microscopic threads.
  • Causes ring to screw onto the cone and stick.

3. Preventive Polishing Procedure

If you’re building a transmission with new gears:

1. Polish the gear cone surface.
   • Start with 400-grit sandpaper.
   • Finish with 1500-grit for smoothness.
   • Can be done by hand if no lathe is available.
2. Check for edge lips or burrs.
   • Use a grinder or file to remove sharp lips at the end of the cone.
   • Inspect for dings or dents.
3. Result: A smooth, burnished surface that prevents the ring from locking onto the gear.

4. Lubrication Best Practices

Use proper lubricant before shipping or assembly:

• Recommended: Joe Gibbs Driven HVL High Viscosity Lubricant.
  • Stays in grooves of the ring.
  • Thin enough to prevent metal-to-metal contact.
  • Remains effective during long storage or shipping.
• Alternative (less ideal): Royal Purple Max-Tuff Assembly Lube.
  • Too thick for long-term storage.
  • Tends to migrate out of ring grooves over time.

Application Method:

• Apply lubricant evenly around the synchronizer ring grooves.
• Lightly coat the cone of the gear.
• Assemble with lubricant in place before shipment.

5. Fixing a Transmission Stuck in Two Gears

If you receive or encounter a transmission that won’t turn:

1. Set all shift levers to neutral.
2. Insert a driveshaft yoke into the tailshaft.
3. Rock the input shaft while turning the yoke back and forth.
4. Ensure transmission has oil so the lubricant penetrates the rings.
5. If necessary, lightly tap and repeat rocking motion until free.
6. Once freed, input and output shafts will turn independently.

6. Key Takeaways

• Never shift a dry transmission on a bench.
• Always polish gear cones before assembly.
• Use high-viscosity lubricant for protection.
• Relieve any lip edges or burrs before final assembly.
• Test for free movement of synchronizer rings before shipping.

7. Recommended Products

8. Conclusion

By taking time to polish, inspect, and properly lubricate synchronizer components, builders can prevent the appearance of stuck transmissions and avoid costly customer complaints. Proper prep ensures smooth operation, longer life, and satisfied buyers.