Rear brake rubbing pt.2

[Acooljt]

Yeah, we had this discussion before but some new info has come to light. I put the bike(79 GS850) up on it's stand and gave the back tire a spin and it barely moved 1/8th of a turn. Yeah, so something is definitely wrong with my rear brake.

As of right now, the bike is not in my possession(it's at the shop having the valves timed which was causing my poor running issues, or so I hope) so I can't bleed the rear brake, but I feel pretty confident that it doesn't need bled. The kid who owned it before me rebuilt the entire rear caliper and I figure if he's smart enough to do that, surely he's gotta know to bleed the brakes, not to mention that it would have to be a pretty big air bubble in the line to cause that much drag(remember, barely an 1/8th of a turn).

So, any ideas?

[SkeletonLake]

My first thought is that the rear wheel nut was way over torqued. My second thought is never mind what the previous owner 'fixed'. Get a Clymer manual and trouble shoot on your own (or with a buddy) or have the shop give it a look see. Is the rear wheel aligned properly? Remove the caliper from the rotor to see if the piston is moving or was it forced back in cock eyed on the reinstall. My last concern from what you posted would be looking for bubbles, at least at this point. Good luck and take your time, you'll find the problem in time.

[renobruce]

Your master cylinder is probably gunked up and won't allow the fluid to return to the reservoir. Or you have an alignment problem with the rotor/caliper? The piston could also be sticking.

[SqDancerLynn1]

MAKE sure the brake pedel move freely, not sticking

[SabreJim]

Hello, I have repaired several master cylinders with this problem. As Renobruce stated, the return hole in the resevour is probably filled with rust and gunk. I had to disassemble the master cylinders (so you dont poke the seal) and work a strand of wire (from a wire brush) into the return hole. It is that small of a hole.

[JayH]

More than likely one of the 2 pistons in the rear brake caliper aren't retracting because it is stuck from dirt/gunk getting past the seal.

[SabreJim]

2 holes in the master cylinders, the larger one puts brake line pressure to the calipers. The smaller one that is the size of a piece of wire from a wire brush, allows the fluid to return to the resevour. If the return hole is clogged, you will get a ratcheting effect on the caliper piston and it wont retract causing the brakes to bind. If you bleed the caliper it will only releive the pressure for a period of time. I think this mess only happens on these older bikes that sit for long periods of time but unsure. It realy is a simple fix if this turns out to be the case with your bike.