06 YZ450F tranny questions

Hey guys. New to the site. My 06 450 has about 200 running hours on it. The case has never been cracked. I give regular oil/filter changes. The last two rides my 5th gear seems to pop out, then back into 5th, when applying more than quarter throttle. Every other gear is strong! Not going to lie but I like to wheelie up to 5th, and hold it up there for a bit. Could this be one of the causes? Or could it be its time to look inside. Or is 5th on its way to being toast? Thanks.

It has nothing to do with wheelies, but it is a wear problem that can only be addressed by a full tear down.

If when you apply a load beyond a certain point in fifth, or any particular other gear, the bike responds by jerking violently as if it slipped out of gear and immediately slammed back in, what is probably happening is the locking lugs on the sides of the two gears involved have become rounded and lost their undercut. The no longer hold themselves together under a load, and instead are forcing themselves apart against the shift fork. Once they clear each other, the drive force is lost, and the roll around until the next slot lines up. Since the fork can't be moved out of the way by this as it can in a car, it holds pressure against the gears and re-engages them again as the gears align, slamming it back in gear again.

The fork will be bent by this, and will need to be replaced, along with the 5th and 3rd "pinion" gears (on the main shaft). Be sure to inspect the others.

Thanks, looks like i'm going to have to spend more money.

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