Front brakes 1981 GS850G

[Guest]

I have rebuilt the front master cylinder twice (the second time to ensure that the return hole was clear), tried to bleed the brakes manually but had to resort to the mityvac which got fluid to come out of both bleeders. There seemed to be a ton of air in there which I have been patiently trying to remove, but do not seem to be getting anywhere. I know from the search that this can be a difficult task. Presently I get only brake fluid through the right bleeder, but still get air bubbles through the left. I have checked all the connections for tightness etc. The brake lever comes back to the handlebar. I would appreciate any hints or advise on this topic.

[2BRacing]

During my previous rebuilds of front m/cylinder, I used a plastic medical syringe to "inject" brake fluid into the inlet hole at bottom of reservoir to first prime the m/cylinder and get rid of most air before connecting to brake hose. This resulted in only a little bit of air needing to be bled from caliper end. Also I used OEM kit for rubber seals - in my opinion brakes are too important to trust to unknown quality aftermarket rubber parts which could swell / fit badly. Hope you easily find the cause of your problem!

[salty_monk]

You may need to bleed the banjo bolts....

Dan

[chef1366]

Take off the line at the junction going up to the M/C. Put the end in the brake reservoir and make sure the hole is submerged. Squeeze the brake lever slowly and watch all the pretty bubbles until they are gone. Now the M/C is bled out. Now you should be able to push fluid to the calipers.

[ardbeglily]

more help

Thank you chef1366, the bleeding of the m/c worked well as I got all those bubbles out. Unfortunately there is still a ton of air coming out of the bleeders. I am just not sure if this is normal or do I have a leak somewhere in the system. There just seems to be no way there is that much air in the system. My other concern is that the pistons are pushed all the way into the calipers in order to get the calipers back on. When will they actually move and allow fluid into that space. Still confused, but constantly learning.

[Nessism]

When using a mity-vac there will be lots of air sucked into the bleeder hoses unless you wrap them with some teflon tape. Has the hand lever firmed up? If so, there might not be as much air in the system as you think.

[ardbeglily]

Thank you Nessism

thank you once again Nessisim for your help. I have wrapped the bleeders with Teflon tape. The handle is still soft and easily pulled to the hand grip. There just seems to be a ton of air. Thank you

[SqDancerLynn1]

Do you have the original brake lines ? The one bike that I had problems bleading ended up having bad brake lines..

[ardbeglily]

I have installed new SS lines.

[ardbeglily]

befuddled GS850 brakes

I rebuilt the front calipers and the master cylinder. I replaced the OEM lines with SS lines from HEL. I wrapped all the banjos and bleeders with Teflon. I have had lots of air in the lines and the brake lever comes all the way back to the grip. I even got the Mityvac on the job. Currently there does not seem to be much air coming out but the lever still goes back to the grip. I am concerned that the pistons have never come out of the calipers since the rebuild and wonder if this could be contributing to the issue. The front wheel still runs free and there seems to be no brake pad friction (the brake pads are new). I have tied the lever to the grip for a few hours but on my return all the banjoes are leaking. HELP

[chuck hahn]

I would say take a second look inside the master cylinder..is everything in the right way? one of the rubber cups in backwards maybe?? You can go to bikebandit and look at the exploded view to double check how everyhing goes...

[ardbeglily]

thanks chuck

At this point I'll try anything including getting that damn circlip off again. I have been able to bleed the lines all the way to the calipers so that all the bubbles come out and then just fluid, so I think the m/c might be ok. I will next pull the calipers off and see if the pistons move, which is someone else did on this site. Thanks again.

[chuck hahn]

I may be wrong..but it seems to me that if the master is working properly, you have disassembled the calipers, cleaned the pistons and seals, got fluid from the calipers and no bubbles... then the master cylinder should have no problem pumping and causing enough pressure to seat the brake pads against the rotors. this is whats making me think theres something wrong in the master.. might generate enough pressure to push fluid to bleed the lines, but not generate enough to push out the pistons.. I have lots of experience rebuilding calipers and masters and they all basically work the same in principal, so thats whats driving me to believe theres a cup in backwards or something..just my thoughts here..

[ardbeglily]

thanks chuck

Thanks again Chuck, the only cup in there is the one that sits on top of the piston and under the spring. The pictures on Bike Bandit etc do not give a great view, but I think I put them back in exactly as I found them. Back to work and thanks again.

[coolksprt]

hopefully this helps. I had a problem for a while as well. The rubber expanded, but that doesn't sound like your problem.
Kev