rear brake drum piston?

not a big job remove wheel. brake drum. &brake shoes .grip the flexi hose leading to the cylinder with mole grips or some sort of clamp to stop fluid leaking when you disconnect the pipe. remove the
2 or3 securering bolts at the rear of the back plate you may have to tap it out. replace with new one normaly about a tenner or under. fit new cylinder replace shoes and drum release thepipe clamp and bleed the brake the rest of the system should be ok

pops
September 2008