I recently got an '86 TRX250R and was trying to get the rear brake to work on it. When I got it, the brakes needed new pads and bled, so I did all this, now the calipre somewhat moves and the brakes do work a little, but I cant get them to go any more than what they are, and thats not much at all.
The guy I got it from replaced the stock R master cylinder with one off a 300EX and I was wondering if this may be the problem. Would the master cylinder off the EX not have enough power to push the caliper all the way on the R? Or maybe I just need to keep bleeding them, I suppose its possible I still have a little air in there somewhere? But I have run about 3 reseviors full through it and it would seem that it should be pressuring up by now.
Please help.

 

You probably need a new seal and pistion kit. The rear 250r brake is a dual pistion set up. I dont know if the 300ex pistion is the same size.

 

The 300EX master cyl should be plenty. Assuming that you have no leaks, is the brake pedal bottoming out without locking the rear axle? I like to pump brake fluid into the caliper & up through the rest of the system. Use a pump oiler, about the size of a small can of spray paint. They usually have a thumb pump or an index finger pump. Buy a new one(a few bucks) or clean one up real good & put brake fluid in it. A small piece of vinyl or rubber hose pushed over the end of the oiler & then over the end of the caliper bleed valve. Empty the resevoir & open the bleed valve & pump SLOWLY. After you fill the resevoir then bleed normally for a few strokes of the brake pedal. Works on my 250R.