Rear brake master cylinder


Information and questions on GL1200 Goldwings (1984-1987)
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1taimar2
Posts: 4
Joined: Sun Apr 21, 2013 1:02 pm
Location: California
Motorcycle: 1985 GL1200 Aspencade

Rear brake master cylinder

Postby 1taimar2 » Sun Apr 21, 2013 1:11 pm



I just rebuilt my rear master cylinder on my 1985 Aspencade and cant get any fluid to flow to my calipers on the rear or the front. I can't find an exact diagram on the rear master cylinder. I am sure I put it bake together the same way it came apart. Doe's anyone know if both rubber plungers go in the same direction or what is the orientation of the the whole piston and plungers. Or doe's anyone know of a diagram and breakdown of the rear master cylinder.



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virgilmobile
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Re: Rear brake master cylinder

Postby virgilmobile » Mon Apr 22, 2013 9:29 am

The rubber has a leading lip...it goes in the bore first...
Be certain both holes are clear.There's the main feed hole and in front of it is a tiny bleeder hole.
Bleed all the air out of the master cylinder before installing it on the bike and bench test it.
Bleed the fluid fron the front brake slave cylinder first and then the rear.
Use the Mity Vac system if it's avaiable.

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Fulcrum
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Re: Rear brake master cylinder

Postby Fulcrum » Mon Apr 22, 2013 12:26 pm

Did you install the rebuilt master cylinders dry? If so then they can't pump any fluid. You will need to prime them and the lines first.

1taimar2
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Motorcycle: 1985 GL1200 Aspencade

Re: Rear brake master cylinder

Postby 1taimar2 » Tue Apr 23, 2013 6:49 am

Thanks for the information guys. I have done all the things posted, bench bleeding and such. my problem is that no fluid is leaving the reserviour. I have checked both front and rear calipers to make sure they are not stuck. Is it possible the bore on the master cylinder is worn and by-passing back to the reserviour? The bike has 96,000 miles on it, other than the rear master cylinder and tire and oil changes thats all I have had to do to it. I don't think I mentioned that this is the second time I have had to rebuild the rear master cylinder. Anyone have any ideas?

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virgilmobile
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83 GL1100 I
83 GL1100 standard
84 GL 1200 I

Re: Rear brake master cylinder

Postby virgilmobile » Tue Apr 23, 2013 9:14 am

Just one idea.the piston is not returning back to the "C" clip.if it is short stroked due to the linkage adjustment,the seal won't pass the feed hole.
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If it bench tested OK it should also work on the bike.loosen the lever till there's free play.

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WingAdmin
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Re: Rear brake master cylinder

Postby WingAdmin » Wed Apr 24, 2013 8:36 pm

virgilmobile wrote:Just one idea.the piston is not returning back to the "C" clip.if it is short stroked due to the linkage adjustment,the seal won't pass the feed hole.
Follow me?
If it bench tested OK it should also work on the bike.loosen the lever till there's free play.


Right. When the brake lever is released, the stirrup/pin should be loose - if they are tight, and still applying pressure to the master cylinder, that could be the problem.

1taimar2
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Re: Rear brake master cylinder

Postby 1taimar2 » Fri Apr 26, 2013 10:52 am

What is the exact positioning of all the components of the rear master cylinder? If I were looking at the master cylinder like it was mounted on the bike, what is the order of all the internal parts of the cylinder. i am thinking something may be in backwards not pulling fluid into the cylinder.

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WingAdmin
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Re: Rear brake master cylinder

Postby WingAdmin » Mon Apr 29, 2013 10:09 pm

1taimar2 wrote:What is the exact positioning of all the components of the rear master cylinder? If I were looking at the master cylinder like it was mounted on the bike, what is the order of all the internal parts of the cylinder. i am thinking something may be in backwards not pulling fluid into the cylinder.


Hopefully this will help:

Rear Master Cylinder
Rear Master Cylinder

1taimar2
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Re: Rear brake master cylinder

Postby 1taimar2 » Wed May 01, 2013 1:30 am

Thanks for all your help Wing Admin, I am still having troubles with this d#%*n thing. I looked at the drawing you sent and I am certain everything is correct. Any suggestions on a fool proof bench bleeding technique? I have tried a Vaccula system to try to pull fluid through and just about every other thing one could try. I am not a shade tree mechanic I have worked on cars and trucks my whole life and motorcycles can't be any more different, just smaller components. One question I do have is if I use a Vaccula system do I have to press the brake pedal down? Or do I just use it like a normal master cylinder?

highplainsbubba
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Motorcycle: 1986 GL1200 Interstate

Re: Rear brake master cylinder

Postby highplainsbubba » Wed May 01, 2013 8:35 am

What I have done in the past is to get a clean oil squirt can and put a hose on it. Fill the can with brake fluid. I put the hose on the brake cylinder bleed port and pump fluid from the brake cylinder back to the master cylinder. Then I watch for fluid filling the master cylinder reservoir. The brake system on my bike seems to be notoriously difficult to bleed, so this works for me. This is the way I do the front brake system as well.

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WingAdmin
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Re: Rear brake master cylinder

Postby WingAdmin » Sun May 05, 2013 10:55 pm

highplainsbubba wrote:What I have done in the past is to get a clean oil squirt can and put a hose on it. Fill the can with brake fluid. I put the hose on the brake cylinder bleed port and pump fluid from the brake cylinder back to the master cylinder. Then I watch for fluid filling the master cylinder reservoir. The brake system on my bike seems to be notoriously difficult to bleed, so this works for me. This is the way I do the front brake system as well.


That's the way airplane brakes are normally bled as well, and it does work well if you can do it. You could also try using a small grease gun - the grease fitting will fit over the bleed nipple, and you can use the grease gun to pump the brake fluid up into the master cylinder. Use a brand new, clean grease gun! You don't want to pump grease into your brake system.




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