Adjusting the Gearbox on CJ750, M72 & K750 – Guide & Tips

Adjusting the Gearbox on CJ750, M72 & K750 – Guide & Tips

Rough shifting, a slipping reverse gear or grinding noises are common problems on classic CJ750, M72 and K750 gearboxes. The cause is usually an incorrect adjustment of the shift segment and locking pins. In this guide, we’ll show you how to correctly adjust your gearbox.

Including a workshop drawing from the original repair manual.

Common shifting problems

Typical symptoms of incorrect gearbox adjustment:

• Gear jumps out under load or high RPM
• 2nd or 3rd gear is difficult to engage
• Shift pedal does not move through its full travel
• Reverse gear slips or engages stiffly

Step-by-Step: Adjusting the Gearbox in 4 Steps

1. Diagnose the issue:
When shifting up, the shift segment may travel too far and the detent ball misses its groove. When shifting down, the segment may not swing far enough.

2. Loosen the locknut:
Depending on the problem, adjust either the upper or lower adjusting screw of the locking pin. First, loosen the locknut.

3. Fine-tune the adjusting screws:

• Gear jumps out on acceleration? → Tighten the lower screw
• Gear hard to engage? → Loosen the upper screw
• Shift lever travels too far? → Screw in the upper screw

4. Check your work:
After adjustment, press the shift pedal through its range and check if the detent ball securely locks into position. The original workshop drawing shows the correct end positions of the gears – an invaluable reference!

The diagram clearly shows correct and incorrect shift positions. Precise alignment saves a lot of trouble on the road.

Important Note on Power Transmission

Avoid unnecessary disassembly of the transmission mechanism. If it’s necessary, always reuse or replace the same adjustment shims. After tightening the nuts, the gears should still turn easily by hand. Too much play means you’ll need a thicker shim.

Conclusion

The gearboxes of the CJ750, M72 and K750 are robust but sensitive when it comes to shifting precision. Proper adjustment ensures smooth gear changes and prevents damage to the shift mechanism. With patience and method, you’ll get a perfectly functioning gearbox with a reliable reverse gear.

Ideal for both solo and sidecar riders!