Spongy front brakes


Information and questions on GL1100 Goldwings (1980-1983)
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Bombasstic
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Joined: Sun Dec 02, 2012 9:49 am
Location: Worcester, Western Cape, South Africa
Motorcycle: 1980 GL1100

Spongy front brakes

Post by Bombasstic »







I have bled my brakes using various methods but to no avail. I just can't get any decent pressure built up. If I pinch either tube, it is better - but with both open it is not good. I found some pitting on the cylinders and had them repaired but still no joy.
I have had new tubes made so "bulging" is not the issue.
What I did find is the 2 Shims (#11 in pic) is missing but I have been told by our local "expert" that these are not necessary and were discontinued.
I bought an aftermarket master cylinder but found no difference so re fitted the origional.

Any advice will be appreciated.


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Rambozo
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Re: Spongy front brakes

Post by Rambozo »

Try pressure bleeding or reverse bleeding. That always works for me.
Some folks have found strapping the brake lever overnight can also help to get that last bit of air out.

How is the lever travel?
Is it the same stationary as when moving?
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Bombasstic
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Location: Worcester, Western Cape, South Africa
Motorcycle: 1980 GL1100

Re: Spongy front brakes

Post by Bombasstic »

Thanks for your reply.
I have bled every which way but loose and I'm sure that air is not the problem.
I took the tubes in to our local hydraulic shop and they confirmed the pipes were good.
When I clamp the left tube and bleed the right side the pressure is perfect ... and when I camp the right tube and bleed the left side it is also good... but as soon as I release both tubes the pressure drops and the lever needs to be pulled way back to get any decent pressure.
My thinking is now, athough the master cyinder is working perfectly, is it the right master cylinder for my GL1100? Coud it possibly be a master cylinder from a bike with only a single disc brake ? iow coud it be the MC is not pushing out the correct volume per lever pump?
Clutching at straws I measured the volume to be +- 7ml per pump.
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OldguyGlen
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1980 GL1100 STD/Vetters
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Re: Spongy front brakes

Post by OldguyGlen »

Spongy is different than stroke or "pumping" problems. Spongy is a softness feeling and is attributed to air since you have ruled out hose bulging. On the other hand needing a very full stroke, or even pumping the lever to get pressure, can be capacity problem. Is the feeling soft (spongy), or is it hard and firm after executing a nearly full stroke, or pumping of the lever.
If Spongy, then there is still air in there. Try bleeding at the master cylinder hose fitting. I have had success with the "bungee strap the lever overnight" technique.
You can double check master cylinder capacity by part numbers, or bore diameter, if the lever ends up firm but takes too much travel or pumping to get there.
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Bombasstic
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Location: Worcester, Western Cape, South Africa
Motorcycle: 1980 GL1100

Re: Spongy front brakes

Post by Bombasstic »

I followed the advice of clamping the brake lever overnight and there was a definate improvement but still not what it should be.
Would anyone have the bore measurements of the correct master cylinder. I don't find any marking on this one but I have measured the diameter to be 12.5mm.
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Bombasstic
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Location: Worcester, Western Cape, South Africa
Motorcycle: 1980 GL1100

Re: Spongy front brakes

Post by Bombasstic »

CORRECTION - The diameter is +-16mm
slickster
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Re: Spongy front brakes

Post by slickster »

I have had success by tapping on the calipers, lines, and connections lightly, then slightly squeezing lever, a tiny bubble comes out every time for a while, the bore diameter should be ok


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