i had to replace the rear caliper pistons on my 85. the hard chrome was worn off and there were burrs on them. the burrs wouldn't allow the pistons to retract. replacements were available from the dealer, i got them from chicago hd and got the 20% discount. if i remember correctly they were about $40 each and i needed two.

 

I also had this problem about two years ago on my 88 FLHS and rebuilt the master and caliper. The other day on a ride the back brake started to drag to the point where it was almost locked up. I am thinking that it might be the hose to the caliper collapsing and acting like a one way valve holding fluid in the caliper.

 

I have had a very similar issue with my Performance Machine rear brakes. Keep in mind, this is a rigid, in which the brakes are directly mounted to the frame, as well as the motor, with "NO" rubber motor mounts, etc... so maybe vibration is causing some of the issues in my case, not sure.

Seems like after 5 or 10 miles lately, I have to stop on the side of the road and bleed the rear brakes because they gradually start locking up (pedal gets hard, can't push the pedal down at all).

Any advice?

 

Chris, most likely either the rear master cylinder itself or a misadjusted master cylinder. See if you can adjust the return point of the pedal so the rod is further out of the MC.

 

Thanks guys for all the great advice. Here is what I found.

I pulled the caliper and the pads were in good shape, about a 1/4" material on both sides, they are in good condition. The bottom pad shim(stainless steel) was kinda notched and cracking/broken, the top one was in good shape. The brake pins were clean w a bit of lube. The piston to pad shim had seen better days and was kinda falling apart. The piston was fairly clean and the boot was in good condition. I cleaned the brakedust from the caliper and bled the brake. The fluid was dirty, I say this cause in the resivor it had what appeared to be a "milk drop" in the fluid, Maybe condenstation/water?? I bleed/flushed the rear caliper with about 4 oz. It seemed hard to build pressure when bleeding (like it took 7-10 pumps after to be "tight", dont know if this is normal as this is the first time I have bleed HD brakes. when pumped the pedal action was good. I cleaned the MC but could not find a "vent hole". Not having spare brake hardware, I massaged the bad pad shim and put that on top and the bad shim on the bottom. cleaned and slighty lubed the brake pins.

After a ride it has appeared that the prob is gone. The brake pedal action is good with no binding.

Chris76, my bike would act up as you described, when it dragged the pedal would be hard the last time. I did not find any binding in the caliper piston, no leaky fluid and all componets seemed to be in good working order except for aformentioned pad shims. I dunno maybe air or water in fluid was my cause along w/ pad shims. It seems to be working ok now. I still need to get new pad hardware I think, but did what I could with what I had at the time.