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Discussion Starter #1
Original problem was brakes stay engaged after lever released. Calipers were sticking.

Completely disassembled both calipers, cleaned them up. For completeness I also replaced the master cylinder plunger, seals, washer and snap ring.

There are no leaks. The calipers no longer stick. I bled both calipers until no bubbles (probably flushed 3/4 of a quart of fluid).

But the brakes are still spongy as if there is air still.

If I clamp off either rubber brake line (left or right) one at a time the lever is firm and does not pump up at all.

But as long as both lines are unclamped the lever is spongy and pumps up, then when released immediately is soft and goes all the way down.

Any ideas what to try next?
 

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Take the calipers off 1 at a time and hold them up as high as the line will allow with the bleeder straight up and see if you get any air from them.
 

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Discussion Starter #4
Bled by hand. Tried gravity bleed but no flow. Tried vacuum but drew air from around nipple.

Did not tie lever to throttle, nor raising calipers one at a time. Will try both next (one at a time starting with lever since that is easiest).
 

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Bad idea clamping the rubber lines. The old lines may be brittle and the rubber inside the lines will crack and restrict the flow, or act as a check valve not allowing the fluid to flow in one direction. I had this happen on an older Oldsmobile after front brake service, laying the caliper on the frame, bent the hose. When I pulled out the brakes worked one time, then locked up.
 

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Consider replacing the rubber lines with braided stainless steel lines.
 
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Discussion Starter #8
Thanks for these comments. Indeed I worried about clamping 40 yr old rubber lines. But figured if they split that was their way to tell me to replace. They are still in good condition (at least from outward appearance).

None the less replacing lines might be appropriate as recommended.
 

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Are you bleeding by hand, or do you use a pump?

Did you try tying the lever to the bar overnight?
Dennis, what is the theory behind this? I've been rebuilding the brakes on my 1100. I think the front still has a little air in it.
 

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From totally empty lines you need a mighty-vac to get them full enough to bleed them in the traditional way, speed bleeders are good for the final operation, especially if help is hard to find.

But if the brakes not coming off was the initial problem then you need to pay particular attention to the small return hole in the master cylinder when you do your cleaning, I still have nightmares about how that almost affected me!
 

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Discussion Starter #13
Update: the technique from "Bike... and Dennis" of tying the brake lever to the throttle overnight worked. The brakes are firm even after sitting for a few hours.

As an avid SCUBA diver I was particularly pleased to read the wiki article an learn all my brakes needs was a decompression stop ;-)

Thanks for all the help. I will of course follow up on replacing the brake lines.
 

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Update: the technique from "Bike... and Dennis" of tying the brake lever to the throttle overnight worked. The brakes are firm even after sitting for a few hours.

As an avid SCUBA diver I was particularly pleased to read the wiki article an learn all my brakes needs was a decompression stop ;-)

Thanks for all the help. I will of course follow up on replacing the brake lines.
This is interesting, I read the Wikipedia page too, but have a question. Henry's Law states that the amount of dissolved gas in liquid is proportional to its partial pressure above the liquid. If I'm understanding this, air above the MC reservoir is one atmosphere and does not change with the MC piston compressed. What changes is the pressure of any air bubbles in the system. After all, with the MC piston compressed the check valve at the end of the piston is closed blocking the brake fluid from the atmosphere. Fluid does not compress, but any air bubbles would. In effect any air in the system will dissolve into the fluid in the system.
My last two bike builds have resulted in varying satisfaction with the brakes. On my CB450 the front is spongy and I have redone it twice. On the GL1200 the rear pedal is spongy, but the front came out nice. On the 1200 I used the plugged hole in the bottom of the caliper to reverse bleed. It pumped fluid up from the bottom and from the vary beginning it worked perfect. I have tried reverse bleeding, vacuum bleeding and old fashioned pumping the brakes.
I'm working on my GL1100 now and bleed the brakes last weeked. The front is OK, but could be better. The rear on the 1100 came out like the 1200 and is very disappointing. I will go down to the garage tonight and tie the front down on the 1100 and I will report back if it got any better.
I worked in a gas station when I was a kid and one of my jobs was to bleed brakes when the shop guys did a brake job. I will never forget the pressure bleeder they had. There was a plate that sealed to the top of the master cylinder and shop air would pressurize a tank that fed brake fluid under pressure to the brake system. Once the system was setup, all that was needed was to go to each slave cylinder and let off the fluid. There was never an issue with spongy brakes.
I putting together a similar system to use on my bikes. I have an older air conditioning flushing tool that I'm converting to a similar tool. I should have it ready to goo next week. I will report back.
 

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I worked in a gas station when I was a kid and one of my jobs was to bleed brakes when the shop guys did a brake job. I will never forget the pressure bleeder they had. There was a plate that sealed to the top of the master cylinder and shop air would pressurize a tank that fed brake fluid under pressure to the brake system. Once the system was setup, all that was needed was to go to each slave cylinder and let off the fluid. There was never an issue with spongy brakes.
I putting together a similar system to use on my bikes. I have an older air conditioning flushing tool that I'm converting to a similar tool. I should have it ready to goo next week. I will report back.
I have one of those but I haven't gotten around to making an adapter for motorcycles. They do a much better job than vacuum bleeders.
 
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I have one of those but I haven't gotten around to making an adapter for motorcycles. They do a much better job than vacuum bleeders.
Dave, I don't want to hijack dbnewton's thread, so I will start a new one with the bleeder. One question, what pressure does your bleeder work at? I got into a debate with a BMW guy and he thinks 2-3 psi is enough. I was thinking 15 psi would be OK. He was concerned the device would come apart and blow brake fluid all over.
 

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Dave, I don't want to hijack dbnewton's thread, so I will start a new one with the bleeder. One question, what pressure does your bleeder work at? I got into a debate with a BMW guy and he thinks 2-3 psi is enough. I was thinking 15 psi would be OK. He was concerned the device would come apart and blow brake fluid all over.
I always ran it at 15-20 PSI on cars. Probably less would work on motorcycles.
 

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Teflon tape on the bleeder thingie... 2..wraps to try to keep air from being sucked past the threads if using an E bay $1 1" bore syringe and clear hose sand and super glued to the end of the plastic syringe (also avail at farm supply stores). then can watch the air bubbles cum thru the hose while sucking the old nasty brake fluid thru the system... should use turkey baster to suck old nasty brake fluid out of master cylinder, before starting to bleed the system so don't run all the old nasty fluid thru the brake system. tap the caliper with small hammer to release any air bubbles that are caught in the caliper?


I thought I read something abt the rear brake being BAD to bleed cuz of the proportioning valve for the combined brakes or whatever the thing is called that use the foot pedal to operate one of the front calipers and the rear caliper. was watching some MotoGP riding teacher telling the class, at the beginning of class, "forget that rear brake"... Moto GP riders go into turns carrying the rear tire off the ground... back brake is not going to do much good with the wheel off the ground. FOLLOWING DISTANCE... its NOT nutt to butt at any speed... contrary to what u see in ur rear view mirror more often than not.
 

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Discussion Starter #20
1980 did not have the proportioning, so no worries there. The challenge bleeding the back brake is being on both sides of the bike at the same time, but it's doable.

I will now get a chance to try some techniques mentioned above. My front brakes continue to work fine but yesterday during a ride the rear lever was way too high. The snap ring in the rear master cylinder popped out. So I'm rebuilding the rear now ?
 
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