I am getting ready to split the cases on my 400EX to fix the tranny and would like to know what, if at all, should I change for maintenance (99' 400EX race quad).

I believe the bearings will be fine. So far I am only going to change what needs to be replaced (shifter fork) and the clutch pack.

Have you heard of any internal parts breaking?
I have heard of 2nd gear breaking on race bikes just like the 250r' and I am considering changing or magnafluxing the gears to be on the safe side.

Thanks for the help.

 

If the engine is still in the frame and chain still on, go ahead and take the clutch pack out and take the retaining nut in behind it off (it's a bear with the engine laying on a table). Be careful with the washer(s) placement for the clutch pack. If the washers are'nt in their correct location, the clutch won't work once re-assembled.