Hi,
My rear brake doesn't work. With fully pressing down the rear brake pedal, bike slowly stop only when I go below 10 mph. I drained brake fluid and made sure there were no airs in the brake line. The brake still doesn't work.
How can I fix this?

 

The piston in the caliper may be stuck or your master cylinder may be bad. Try cleaning the piston first before getting the new rear master cylinder.

Take the rear caliper off only 2 or 3 bolts and hold it so you can see it and when you press the brake lever the piston should move just a little. If that doesnt work just clean the piston.
Take the brake pads off.

To get the piston out you can use some pliers with rubber tips or just a towel around it. You dont want to damage the piston in any way. Take the piston out and drian the brake fluid. Use a scotch bright pad to clean the piston and then lube it with some brake fluid.

Now the quick way to help keep alot of air out of the line is to pour break fluid in the fluid cup(where you normally add fluid) until it fills the piston hole to the top. Put a towel around the brake fluid resivor cause this next step will cause it to overshoot the top. ( MAKE SURE YOUR LID ISNT ON OR IT WONT WORK) once you have it filled with fluid push the piston where it goes slowly. The fluid will begin to overshoot the top of the resivor and spill out. Once you get the piston all the way in begin working the brake lever and your piston should start to move out. If it doesnt work then its your master cylinder.

Hope that helps

 

Oh yeah. DONT GET BRAKE FLUID ON ANY PAINTED SURFACE!!!!!!!! If you do say buh bye to that paint.

 

Thanks a lot!
This was from a bike that was garage kept for almost three years.
Do you think I should rather replace the whole thing or at least the calipers?

 

Just try cleaning it at first and adding some new fluid. Dont waste the money if it only takes a lil elbow grease. But if you try the above steps and it doesnt work it can be the caliper.