Brake problem

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Mar 11, 2012 | 10:09 AM

#11

mrfikser

Outstanding HDF Member

Joined: Oct 2009

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From: Maryland near DC

the problem is definitely in the master cylinder...if the bore is the correct diameter then the seals must not be 'right'.......as far as correct fluid, it normally say on the cover what to use...but the wrong fluid wont cause the problem you have ...

Mar 11, 2012 | 10:23 AM

#12

sgdiesel

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Joined: Nov 2008

Posts: 1,296

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From: Cheltenham, UK

Quote:

Originally Posted by mrfikser

Directly the fluid would not cause this problem, I agree. However, there is a potential compatibility issue between the seal material and the fluid, and that can certainly lead to a break down in the integrity of the seal. This has been debated many times here, and my intention is not to take the thread in that direction. The key point is that, whilst doing this, especially when you are mixing and matching systems, you must pay special attention to the seals you use and ensure the entire system has full integrity.

In terms of the master cylinder, depending on which seals you installed, some of the seals do need to be put in the correct way around - although to be fair I am not familiar with this specific master cylinder and it's seal configuration.

Otherwise, look for score marks in the bore of the master cylinder

Mar 11, 2012 | 10:34 AM

#13

sgdiesel

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Joined: Nov 2008

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From: Cheltenham, UK

Quote:

Originally Posted by marvincbr

Forgive me as I do not know, is it possible that I should be using Dot 5 fluid? 2008 was the first year of the new Brembo system on the baggers. Did they use Dot 5 and then go to Dot 4 after that? This is really beginning to get frustrating......

Thank you for helping out...

If I am reading this correctly, you changed out all the seals when you serviced the MC. I don't wont to over complicate things for you, but basically the rubber compounds used are different, depending on the fluid being used.

Ideally, when buying the service kit it should say what fluid it is for. If it is an original kit, then I guess the only thing you can assume is that the compound is compatible with what the cap of the reservoir says.

The breakdown of the seal is not immediate, so if you have just done the change and experienced this on first test then I doubt the seals have broken down already.

In summary though, you should ensure calipers and MC are sealed for the same fluid. In addition to this, and ideally, it should be the same fluid you used originally if you want to reuse the rubber lines.

Mar 11, 2012 | 10:49 AM

#14

DTTJGlide

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Joined: Dec 2009

Posts: 2,561

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From: North Cental Iowa

As others have said it sounds like it is a MC problem, doesn't your original 07 MC use DOT 4 also? If so try putting that MC on & see if that solves your problem, as long as the fluid is the same the earlier MC is compatible, it doesn't work quite as well as the Brembo MC but it will isolate your problem. I'm always leery about using brake parts from a chromer, they just take in cores & as long as they look OK on the outside they chrome them & send them out to the next guy.

Mar 11, 2012 | 01:43 PM

#15

X Iron Butt

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Joined: Jun 2011

Posts: 974

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From: Chesapeake Virginia

Quote:

Originally Posted by marvincbr

I did rebuild it if putting new plunger/seals/spring and retaining ring in is rebuilding....

I did buy this m/c from a chromer on ebay. Is it possible there could be something inside the seal/plunger area causing it not to seal and hold correctly? Would that cause the problem I am describing? Fluid getting past the m/c seals and releasing pressure....

Rebuilding should include honing the bore. If the plater did not plug the hole in the plating process the bore may have been smooth enough to take the chrome. If it was a goog plater it will have copper and nickle under the chrome. My plater did not plug any holes and I had to hone everything he did. The chrome and nickle are pretty hard and took quite a bit of honing to get through it. You have to be careful as if you get through the nickle the aluminum is soft and you can oversize the bore enough the new seal kit will be too small. You don't have to remove all of the plating but should give the bore a good smooth cross hatched look. Be sure and flush real good after honing.

Mar 11, 2012 | 06:19 PM

#16

marvincbr

Thread Starter

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Joined: Dec 2006

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From: Shorewood IL

It seems it was the m/c that I got from the chromer. I pulled it apart to see if I could see any issues in the bore, couldn't really tell. Cleaned it up and tried it again, same problems. Put my original one back on and works like a charm. I will either try to have the bore cleaned out or just bite the bullet and get a new chrome one from my favorite dealer. I want to thank all who helped and were most informative trying to help me figure this out....