Rear brake lock up 78 gs 750

[Tryan31]

So today was my first attempt at brake maintenance on my 78 gs 750e. I have noticed when simply rolling the bike out of the garage a resistance that had been getting more and more severe until today when I went to roll it out and the rear tire wouldn't budge. Upon investigation, the pistons on the rear caliper were pinched tight against the disc. Having never done this before, I troubleshot with BikeCliff's site and Clymer's and went one step at a time. Originally I bled the brakes, nothing changed. I removed the pads and pushed on the pedal a few times, now the pistons were locked flush against the disc. Oops.
Took the rear caliper off, took it apart and cleaned it up according to Clymer. Really nasty stuff in there. 35 year old dirt perhaps? Some rust existed on the pistons but I did everything next to steel wool to clean them up as best as possible. I didn't replace the seals and o ring in the interest of trying to do this in the least cumbersome way possible, but I cleaned them up real shiny and lubed them up with the proper brake fluid.
Threw them back on and went to put new pads in and the disc was sitting snug against the caliper so much that I had to force the outside pad into place. The inside pad had plenty of room. This seemed odd to me, but the pictures on bike cliff's site looked similar enough so I went with it. So now with the pistons pushed in all the way, one pad was already flush against the disc. I bled brakes again, ensured no air bubbles existed, and in the process of doing that, the inside piston had once again compressed on the disc and won't release. The outside piston has nowhere to go, but the two have locked the rear wheel.
A repair kit with seals and O rings was ordered. I'm wondering if I should find new pistons as well? Hopefully I don't need a whole new caliper, but I am thinking that the reason it is so snug against the disc is because the bracket might be bent. It does not look as though that would be the case, however I don't want to rule anything out.
Thank you in advance for your advice. I am about ready to throw the entire thing in the trash and buy everything new... Hopefully it doesn't come to that!

 

[Gonzo]

Sounds like a blocked return port in your master.

 

[Nessism]

If the piston are pitted on the sealing surface they must be replaced or the caliper will leak. You are also strongly advised to replace all the seals and dust covers in the caliper, replace the brake line since it's all full of sludge and the rubber is aged, and tear down the master cylinder to inspect all the parts and clean it out. If the caliper bore is pitted then it should be replaced.

It's ill advised to short cut the process when it comes to brakes.

 

[daturat100r]

Had same problem with mine, new pistons and seal kit from suzuki sorted it for $110 nz.

 

[jwhelan65]

Simply put you have a failed system due to age and lack of maintenance. Start fresh and replace everything that was mentioned above. Calipers usually lock up because the fluid has turned to sludge. A complete tear down and rebuild is your only option IMO.

 

[chuck hahn]

If you remove the seal from the groove in the caliper youll find it full of oxidation and scale. As the scale builds up it takes up space and something has to be displaced because of this scale. The thing that gets displaced is the seal. The seal gets tighter and tighter and tighter around the piston until it will no longer retract the 3 or 4 thousands that it normally would if the seals were properly seated all the way back in the groove. Remove the seals and clean the grooves and the seals and youll not have this problem again...