1979 gs850 rear brakes problem...please help

[Gsbori]

Hi i need help with this bike..3 time and mybrear brakes locked ...i can be riding around for 10-15 min and bikr starts to slow down and thats how i know i gotboff bike n look n saw rear brake lock ,try pushing bike and wouldnt move. I had let presure of the bleeder and it release it.. i took everything apart and cleaned it n still nothing ..i vacum bleeded the system and nada. Im not even sure if ear caliper is the right one cus i seen others with a double bleeder screw system and mine only had 1..help please

 

[Nessism]

Did you split the caliper, remove the pistons, and clean out all the crud in both the calipers and master cylinder? If not, now is a good time. A blocked master cylinder return port (the super tiny hole that allows fluid to move back) is typically a problem on old bikes. Oh, and replace the brake line since it's going to be lined with scale after all these years.

One other thing to do is grease the brake lever pivot shaft.

 

[Gsbori]

Hi thanks for supper fast respond ...yes i took everything everything apart.. im going to order a new line..but its just weird even if i dnt even touch the brake not once still does it..

 

[bwringer]

According to the fiche, the original caliper had two bleeders. Some later calipers had one bleeder. Even though it sounds like yours has been replaced, it could still work fine -- just make sure it's centered and that both pistons are extending and retracting normally.

Sounds like one of the pistons is getting stuck, so it's time to take it apart and install new OEM seals -- the aftermarket kits are junk. New pistons don't seem to be available, but you may be able to clean up the old ones or post in Parts Wanted to find good ones.

As Nessism mentioned, it's also common to find a corroded or damaged brake line, or a clogged return port in the master cylinder (since you mentioned that it slowly locks as you ride, I'd strongly suspect this is the problem). Clean the whole system thoroughly.

 

[jsandidge]

The return port that gets blocked is in the master cylinder, not the caliper. It frequently causes the symptoms you describe.

 

[Steve]

Yet another vote for having the return port in the master cylinder as the cause of your problem. "Been there, done that" more than once.

To find that port, remove the fitting on the side of the m/c, look inside. You will see two small holes. The upper one is the one you are wanting to clear. It might be hard to see, but it's there. Even a single strand of wire might be too large to poke through it, depending on the wire you have available. I have some very fine wire that I use to do the job, but some clogs are tougher than others. For them, I have a 0.5mm drill bit that will clean it out nicely. If you do have to drill out the hole, keep it as small as possible. The 1/16" bit that is typically the smallest in a set might be too large (it's almost 1.6mm).

.

 

[Gsbori]

So i can actualy drill this small return hole ..it is a very small hole..what happens if u make this hole a tiny bit bigger will it b a problem

 

[Nessism]

Don't drill. Just clean the system.

 

[Gsbori]

My question is how will this happen even if i dontbpress the brake..i have it all apart n cleaning now n then test ride...im even rexleaning calipers againg ..i may order parts tobrwbuils the calipper and master..if cleaning dnt do it...

 

[Nessism]

Find and clean the tiny little return port in the master. If you brake lines are original they may contaminate the new fluid though.

 

[Gsbori]

I drop the spring and everything else from inside of master cylinder n cant figure wich way it goes now

 

[Gsbori]

Well got it all together n when arou d n ride it n still locked up againg uhg

 

[Gsbori]

I rebuild calippers and master and still sticking any one can help

 

[fastbysuzuki]

I rebuild calippers and master and still sticking any one can help

Assuming your pistons are moving freely in the calipers and your brake pads also, then as in other posts the return hole is either blocked Or your master cylinder piston is not uncovering the return port to release the pressure.
if I read your post correctly you seem to say this happens even though you do not use the brake in this case the build up of heat from the pads even slightly in contact with the disc will increase the pressure and slowly lock the brake this again is due to the master cylinder return hole not being uncovered one question is this the correct master cylinder for the bike? Is the lever allowing the master cylinder piston to travel far enough to uncover the return hole?

.

 

[Big T]

I rebuild calippers and master and still sticking any one can help

Some more detail would be helpful
Did you replace the seals on the pistons? Did you use OEM parts?
Did you replace the brake line?

 

[Nessism]

And did you run a wire through the small return port hole in the master?

 

[chuck hahn]

Wire from a wooden handled wire brush works for the hole. As for the order of parts. Spring goes in first with the big end going in first. then the cup with the flat side to the top. Then the piston. Then the rushrod secured with the circlip.