2004 suzuki ltz 400 rear brake problem

[Ripcityrider21010]

I bought this quad about 2 months ago and it runs great. When I bought it the guy said all it neede was rear brake pads. I put new pads on it only to come to the realization that the rear master cylinder is frozen. I bought a rebuild kit for the cylinder and had the cylinder working until I put brake fluid into it. I put dot 3 brake fluid in it and tried to mount it and it had seized up again. I tokk it apart again and now the piston won't go back into the cylinder. I was told that the dot 3 brake fluid may have swelled the gasket on the piston. Can this really happen? Any help or suggestions would be awesome. Thanks!

[DirtDemon]

The only difference between DOT 3 and 4 is the wet and dry boiling points. Your problem might be that the parking brake needs to be adjusted out, or the bleeder may be plugged. Have you checked the guide bolts for notching, this will cause the brakes to hang up and possibly get misaligned which could possibly tilt the caliper piston, causing it to hang up. There are many possible causes, but I am sure it is not because you used DOT 3 brake fluid.