Spongy brakes


Information and questions on GL1100 Goldwings (1980-1983)
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binder49
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Joined: Wed Apr 13, 2011 8:26 pm
Location: Mapleton ND
Motorcycle: 1980 GL1100 Goldwing

Spongy brakes

Postby binder49 » Sun Mar 11, 2012 3:09 pm



The brakes on my 1980 GL1100 were spongy. Tried bleeding them, no help. Just switched to braided steel lines. They still feel spongy. I'm sure I have the air bled out. Any help would be appreciated

Thanks
Mike



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seabee_
Posts: 494
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Location: sterling heights, mi
Motorcycle: 1985 Honda Goldwing GL1200
117k miles
1977 Kawasaki kz400
1978 Suzuki GSXr750
1980 Kawasaki GPZ400
1975 Honda CB360T

Re: Spongy brakes

Postby seabee_ » Sun Mar 11, 2012 6:35 pm

Which brakes? Front, back or both? If it's the fronts, you might still have some air in the system. You can try putting the bike on the side stand, turn the handle bars so the brake master reservoir is level(as possible), pull the brake lever and zip-tie it(or use rope) and let it sit over night. That will allow any trapped air to come out of the lines through the reservoir. Did you use a vacuum brake bleeder ?
Paul
CE1 Navy Seabees/RET
1981 to 2002
ASE Mechanic

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binder49
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Joined: Wed Apr 13, 2011 8:26 pm
Location: Mapleton ND
Motorcycle: 1980 GL1100 Goldwing

Re: Spongy brakes

Postby binder49 » Sun Mar 11, 2012 7:31 pm

I used the old method of the two person bleed, one running the lever, the other opening the bleeder. It is both brakes

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seabee_
Posts: 494
Joined: Sun May 29, 2011 8:17 pm
Location: sterling heights, mi
Motorcycle: 1985 Honda Goldwing GL1200
117k miles
1977 Kawasaki kz400
1978 Suzuki GSXr750
1980 Kawasaki GPZ400
1975 Honda CB360T

Re: Spongy brakes

Postby seabee_ » Sun Mar 11, 2012 7:53 pm

The MityVac brake bleeder is the best way to go. @$30 Harbor Freight. You might still try the zip tie overnight trick though. Don't know if it works for the back master cylinder though. Worth a try. Good luck.
Paul
CE1 Navy Seabees/RET
1981 to 2002
ASE Mechanic

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SilverDave
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Location: Langley, BC
Motorcycle: 1985 GL1200 GoldWing Aspy

Re: Spongy brakes

Postby SilverDave » Mon Mar 12, 2012 2:51 pm

Zip tie ( or a binder made of Duct tape), or a brick hanging on the pedal will definitely work on the rear brake as well... Needs overnight !!

The way I had it explained to me was small bubbles in the hose / resevoir, and the sustained , long time pressure allows the bubbles to re-dissolve in the brake fluid.....it may not be true, but that was my mechanics friend's story.....

And once you have gotten the tiny bubbles out ( Overnight ) then carefully bleed with fresh fluid to allow new fluid to replace the old fluid all the way down the lines.


SilverDave

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Re: Spongy brakes

Postby WingAdmin » Mon Mar 12, 2012 3:11 pm

SilverDave wrote:Zip tie ( or a binder made of Duct tape), or a brick hanging on the pedal will definitely work on the rear brake as well... Needs overnight !!

The way I had it explained to me was small bubbles in the hose / resevoir, and the sustained , long time pressure allows the bubbles to re-dissolve in the brake fluid.....it may not be true, but that was my mechanics friend's story.....

And once you have gotten the tiny bubbles out ( Overnight ) then carefully bleed with fresh fluid to allow new fluid to replace the old fluid all the way down the lines.


SilverDave


What happens is when you pressurize the system, the air bubbles get squeezed, and under pressure they become smaller, so that they can migrate up (via gravity) through orifices that they might not otherwise normally fit. For that reason, I don't know that it will work for the rear brakes. Can give it a try, anyway. But best advice is to give the Mity-Vac a try.

That's what I've heard, anyway. :)

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binder49
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Location: Mapleton ND
Motorcycle: 1980 GL1100 Goldwing

Re: Spongy brakes

Postby binder49 » Mon Mar 12, 2012 6:08 pm

Thanks for the advice guys, gonna give the pressure thing a try. You guys make this a great site to go to for help

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SilverDave
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Re: Spongy brakes

Postby SilverDave » Mon Mar 12, 2012 6:18 pm

Well it does work for rear brakes...

and I think the jury is still out on exactly how this works : see here for a long discussion :

http://forums.noria.com/eve/forums/a/tp ... /621104403

and here too ( Myth Busters )- even longer :

http://community.discovery.com/eve/foru ... 2319093301

There appears to be no clear exact answer to the (scientific) puzzle of exactly WHY this works ..
as " Old Guy " points out, he has a 1200 Goldwing and the rear brake lines go above the resevoir and above the two calibers ... If it was gravity only, then the bubbles should congreate at the two high spots ... and not be removed... but they are removed by this method ... so its a puzzle.

The best possible explanation appears to be the hydroscopic nature of the brake fluid. The dry brake fluid adsorbs the water, and changes the ( slight ) solubility of the gases in the fluid..... perhaps the gases dissolve in the water part of this solvent mixture ..............
Time passes ( overnight ? ) ................ the pressurized, possibly partially dissolved gases are now dispersed over a much wider volume of brake fluid , and when the pressure from the tie-down is released, some of these gases/bubbles are released in the resevoir, (where they do no harm)... but much of the bubbles are removed from the lines ... and the brakes become firmer ...
.......
Possibly ...........
................................. maybe .....

Here is a patent for detecting the dissolved air in brake fluid :

http://www.freepatentsonline.com/5361624.html
<Sensor for dissolved air in brake fluid>

so we know some gases can dissolve in brake fluid.

All liquids can ( and do ) dissolve some amounts of gases. Sometimes just traces ... sometimes huge amounts .
That solubility is influenced by the outside barymetric pressure ....
and by the chemical " Likeness " of the solute/solvent .

The chemistry question is :
Is it just a trace amount of oxygen/nitrogen dissolving in brake fluid ?
Or can enough dissolve to purge the lines of some of the air, when under pressure ??

see also here, second last paragraph :
http://www.rs683.com/abc.html

In any case, it does work... whether we scientifically understand it or not ...

SilverDave ( Retired Chemist )




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