Help Yz125 transmission issues

Oct 9, 2021
I have an 03 yz125. in neutral and the bike is off when you roll the bike backwards the transmission locks up but it’s intermittent. It does the same rolling forward but it’s not as bad. I’ve taken the chain off and spun the drive gear and it still happens. it’s also not like it’s grabbing a gear and compressing the piston it’s like hitting a wall and jamming completely. Any ideas to what is causing it


Moderator /
Damn Yankees
Nov 21, 2000
That's an odd one. My first guess would be a shifting dog is worn and it is allowing it to move in between gears. The odd part is that it is locking up. I'd be interesting is what you find after you tear it down.