I searched and found a thread but it ended without a resolution.

I've got a 2003 400ex that has started popping while in third gear. IT feels like it snaps in and out of gear. It isn't making any more funny noises or acting funny in any other gear, only third. I replace the worn out front sprocket with a brand new one. The chain has about an inch and a half of vertical movement and the rear sprocket is in pretty good shape. Just looking for a place to start and some exploded diagrams to work off of. Thanks

 

Myself I wouldn't drive that bike until the transmission was fixed .. I have a 2007 400EX at work now in a box that started out jumping out of gear (and the owner drove it until it had no gears) and now it's being junked because the cost for pars is more than the bike is worth ..

 

What should I look for? Should I split the case? Got any diagrams or directions on splitting the case. I can figure it out and have the tools to do it. Just looking for some more advise

 

I assume you have checked the axle bearings? It will jump sprocket teeth if the bearings are bad.

 

Axle bearings feel tight. Seems like if it was jumping teeth it would do it in all gears. Anyone have some good instructions or tricks to pulling this case apart?