I have a 1990 trx300fw and just recently on the trails my bike stoped going forward, i just grinds like crazy from the rear axle. It catches in reverse but not forward. I looked at the ring gear while my friend pressed the gas in forward and the ring gear doesnt move, just shakes and vibrates. Im guessing its the pinion not catching. Maybe blow pinion bearing. I dont know, i have no experience on working on atvs, just jeeps and axles. Anyone think they know wats going on with my bike so i can get a jump start on to where i start looking? How do i take apart the rear differential? Is there a write up somewhere u can referr me to? thanks

 

You my friend have a pinion gear with some teeth missing. I just finished rebuilding my differential for the exact same problem. Parts will run about $300 for the ring and pinion, bearings, seals, and the shims used to set backlash.

I was going to have it rebuilt professionally by a dealership until I asked how they set the backlash. Their response was "as long as you don't mix up the shims it will go together just fine." This is WRONG!!! Every R&P is a little different and requires the correct shims to set the backlash to .004 to .006. If the backlash is excessive it will cause you to have the exact same problem very quickly. Too tight and it will overheat and seize. I spoke to 3 dealerships and two private shops and they all said the same thing about reusing the shims so I suspect it is a widespread problem.

Its not a very hard job to do, just make sure you get the backlash right and have everything clean inside. The crunched up gear will be everywhere, get it all out. Make sure everything is tight, use avaition adhesive to seal the halves of the differential (it doesn't add clearance to the case like regular silicone does), use good gear lube and change it several times over the course of a few weeks.

 

Very good info and advice. Only thing I would add here is to not even bother replacing the ring and pinion without using all new bearings. That goes for the brake side as well. And a note on the bearings,..do NOT use any brand aftermarket bearings. A bearing is simply not "just a bearing" and the ones offered by PivotWorks, Moose, etc.... total garbage for heavy use. They work fine for swingarms and wheel hubs, but not an ATV differential. Seen hundreds of repeated failures over the years and they werent from improper shimming or stripped parts,....just cheap $$$ bearing replacements.
Another thing you may want to look at is just replacing the entire differential assembly. It runs 600 bucks from most dealers already put together, with new bearings, and shimmed properly from the factory. Just bolt it on and add gear oil. Depending what your time is worth and whether someone was going to do the dirty work for you, this sometimes actually becomes the most cost effective way of getting it done, and done right the first time.

 

Hi what brand of bearings would you advise to use and also Are the aftermarket pinion and ring kits offered on Ebay ok?Thanks

 

Oh and almost forgot.Whats the trick in getting that needle bearing out and the huge odd shaped nut?