03 yz450f gearbox woes

[Mperry48111]

I have a 2003 yz450F. While riding, it will periodically shift itself into first gear. I don't know if this is a clutch issue or a gearbox issue. Any ideas would be greatly appreciated.

[grayracer513]

Sounds like a big shoe issue.

Please provide a more elaborate description of when/how this occurs.

[Mperry48111]

There is no real rhyme or reason to when it happens. That is, it is no more likely to happen when hot than cold. I do have difficulty starting the bike while in gear - it lurches forward when I attempt to kickstart it. I know this suggests clutch issues. I am just hoping I don't have gearbox issues as well.

[grayracer513]

You're not helping.

Does it happen when you're riding? At a standstill? On hard landings? What?

The only way that the trans can change gears is for the shift cam to rotate. A heavy shift lever, a weak or broken centering spring, index lever or spring, or hitting the lever with your foot are just about it.