2003 450, 4th gear problem??

I have an 03 yz450, and it runs and drives perfect until I get into 4th gear. Then it seems like it jumps in and out of gear, kinda like if you were pulling the clutch in and out while on the throttle. It is really bad if your about 3/4 throttle. Does anyone have an idea? Thanks

The locking lugs on the gear pair that locks the trans into 4th (3rd and 4th pinion gears, on the mainshaft) are worn, and have lost the undercut that makes them hold in gear. In fact, the undercut has worn into an overcut, so that the two gears actually push apart from one another against the shift fork, causing them to become momentarily disengaged until the shift fork springs them back into engagement, producing the jerking feeling you get here.

The shift fork will have been bent by this condition, and need replacement as well as the two gears involved.

Just wondering about what you said about the problem with my tranny. Is this a job that the average person could fix by themselves, or would I need to take it to a shop? If I did take it in, what would you guess that it would cost to do? Thanks alot

It's a major tear down; engine out, top off, cases split. A capable home mechanic can do it without too many special tools, but it's fair to say it calls for skills that are above today's average. No guess on prices. You'll have to call around. Won't be cheap.

You may want to consider going up a generation to an 06+, I know that on alot of the older bikes you have to begin to think about the value of putting 1000+ into busting open a bike that might not be worth it in the end.

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