2002 YZ426F Gearbox Issues

Anyone out there heard about gearbox problems on this model. i.e. slipping out of gear.

I've come across a 2002 yz426F with 2nd gear slipping out of drive.

I've been told by a Yamaha Technician it's usually 5th gear that does this.

Have you guys experienced any gearbox problems with the 426F?



That problem does usually show up in 5th, but it could happen to any of them. In your case, you need the 2nd and 4th "wheel" gears (on the output shaft), and the #1 shift fork.

The problem is caused by rounding and wear at the locking lugs and slots of the associated gears. When it starts popping out, the force bends and wears the shift fork.

Check the rest of the trans while you're in there, this may not be the only problem.

Have you tried the search function? It sounds like the locking lugs (dogs) on the sides of the gears. I have not had this problem on my 2000 model yet, but I am sure that there are some posts on this.

Im having problems only in 5th gear just took it on a nice hard ride and cracked on throttle in 5th gear and now it slips let off throttle and its fine then give it a handful of throttle and it slips again im really hoping its my clutch that could use a fine adjustment this is a 2002 Yamaha yz426F. Also could installing aftermarket camshafts have anything to do with the extra increase horsepower on clutch are my last and final question is what about the transmission which im hoping is not a problem please any advise would be gratefully helpful clutch are transmission are could it be both thinks again need the advice.

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If the slip is a smooth increase in RPM like happens when the rear tire spins, it may be the clutch, but if it's jerky like the gears are jumping teeth or something, the problem is wear on the locking lugs on the sides of third and fourth gears on the main shaft.  The wear causes the gears to push away from each other instead of hold together, and this process will most always bend the shift fork as well.

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