Weeping Front Brake Master Cylinder

1260 Views 11 Replies 9 Participants Last post by imst0ked, May 21, 2022

thehueg

Discussion Starter · May 10, 2022

I changed out my brake fluid and after carefully placing cover back on the master cylinder, it weeps a very slight, but noticeable amount of break fluid. I wiped the lid and the tank perimeter and tightened the screws down firmly. What might I have missed that’s causing this?

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Ponch

· #2 · May 10, 2022

You put too much in? I have the old style reservoirs. Could be the rubber seal is bad.

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thehueg

Discussion Starter · #3 · May 10, 2022

It’s below the “Max” line.

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6speedTi

· #4 · May 10, 2022

I had the same thing happen. I cleaned debris from under the seal grove and replaced the seal for the cover. Still ended up seeping out. Was told by the BMW technician that this is normal if you fill it to max level or just above. When the reservoir is tilted to one side or another it will seep out. Keep the level below "MAX" when the reservoir is level or close enough. If it still seeps lower it a small amount again. This solved my problem.

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thehueg

Discussion Starter · #5 · May 10, 2022

6speedTi said:
I had the same thing happen. I cleaned debris from under the seal grove and replaced the seal for the cover. Still ended up seeping out. Was told by the BMW technician that this is normal if you fill it to max level or just above. When the reservoir is tilted to one side or another it will seep out. Keep the level below "MAX" when the reservoir is level or close enough. If it still seeps lower it a small amount again. This solved my problem.
[/QUOTE

thanks. I’ll try that.

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chatrider3

· #6 · May 10, 2022

rubber isn't seated correctly

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beech

· #7 · May 10, 2022

New rubber bellows seal needed once and a while. Don't wait till this happens.

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6speedTi

· #8 · May 10, 2022

Item # 10

BMW PART NUMBER:

32727722331
Boot

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pathy

· #9 · May 12, 2022

I had a small crack on mine in that corner. Check it very carefully, to me in the photo it looks like a crack to me. It's only has to be a hairline crack.

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RTinGB

· #10 · May 13, 2022

My '10 RT had the same thing. Ate the paint off the cover, so I cleaned the seal, and repainted. It happened again, so I ordered a new seal.

While I was waiting for the new seal, I looked at the old one and it looked fine.

So I figured the top was not sealing well. I mounted a Dremel metal grinding bit in my drill press, and ground the area where the screws go through the cover down (not much, half a mil or so, and be sure to shim the cover so it is ground even). Now the cover squeezes the gasket more.

Stripped and repainted the cover, have ridden 300 or so miles and have not had a problem.

Well, one problem - I have an extra master cylinder seal now.

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Brunhilde

· #11 · May 13, 2022

6speedTi said:
I had the same thing happen. I cleaned debris from under the seal grove and replaced the seal for the cover. Still ended up seeping out. Was told by the BMW technician that this is normal if you fill it to max level or just above. When the reservoir is tilted to one side or another it will seep out. Keep the level below "MAX" when the reservoir is level or close enough. If it still seeps lower it a small amount again. This solved my problem.

I had same result on my 2007 RT. Dealer suggested might need new master cylinder, but removing a small amount of fluid did the trick.

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imst0ked

· #12 · May 21, 2022

Brunhilde said:
I had same result on my 2007 RT. Dealer suggested might need new master cylinder, but removing a small amount of fluid did the trick.

A dealer that suggests the most expensive solution. Hmmm. How odd.

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