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  #1  
Old 06-05-2006, 11:14 AM
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MasterCylinder/Booster Question

OK, I've searched a bunch of threads, nothing specific to my particular problem.

Here goes: Last year I replaced the grommets on my master cylinder - couldn't get the back one seated all the way in but it did not leak for some time. Just before I parked the car for the winter I noticed there was brake fluid wetness on the booster below the master cylinder. I tried very hard to determine if the fluid was coming from the rear grommet or the seal between the master cylinder and the booster. It looked like the latter, so I ordered a master cylinder gasket from the dealer. This spring (more like summer) when I was doing many interior odds and ends on the car I took off the master cylinder, cleaned the gasket area very well on the the cylinder and the booster, then reinstalled and bled the system. Oh yea, there was some fluid in the booster, not too much, mayber an inch or so. I suctioned that out with my mitycvac. Ok, all is good right? well, after a day or so on the road, the wetness is back on the booster under the cylinder. Great! Ok, it must be that rear grommet that I could not get the resivior to bottom out on. Last night I take the cylinder off, work it and work it and what do you know, I get the thing to bottom out on the grommet. Hooray, problems over - new gasket, properly seated fluid resivior, freshley bled system (again) I'm good to go. Guess what - this morning the wetness is back.
I'm getting irritated now. Questions are:
1. Is the master cylinder to booster gasket just for a vacuum seal? No fluid should be in the vicinity of that connection should it?
2. Is my master cylinder going bad and there is some leakage that the gasket cannot hold back?

My brakes work well, no pedal fade whatsoever. What is the problem??

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  #2  
Old 06-05-2006, 11:20 AM
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I almost suspect with you finding brake fluid in the booster last year that perhaps the rear master cylinder seal had been leaking. Or could have been a previous master cylinder as well. But at some time there was leakage that should not have been. Others will offer opinions.
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Old 06-05-2006, 12:03 PM
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So you are saying that there is a leak internal to the master cylinder? I need to replace the master cylinder and this annoying seepage below the cylinder on the booster will stop?

I'm still getting the slow seepage after replacing the cylinder to booster gasket and finally seating the rear reservoir leg into the grommet properly.
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  #4  
Old 06-05-2006, 01:13 PM
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The gasket between the booster and mc is for vacuum seal. If there's fluid in the booster you need to replace the MC.
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  #5  
Old 06-05-2006, 01:20 PM
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Quote:
Originally Posted by hockeynut

I'm still getting the slow seepage after replacing the cylinder to booster gasket.
The purpose of the m/c to booster gasket is to provide an airtight seal for the booster, not to contain brake fluid in the m/c. You are changing the wrong part for the wrong reason.

There is usually a "weep hole" near the m/c flange where it joins the booster. An internal leak in the m/c rear seal will allow brake fluid to escape there and run down the front of the booster, making it appear that the leak is coming from the m/c to booster interface. Sounds like it's time for a new m/c.
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  #6  
Old 06-05-2006, 03:21 PM
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Weep hole - excellent explanation. I knew you guys would come through. The more I read the more I figured the gasket wasn't for brake fluid, but I ordered it last fall so replaced it when I removed the MC. I really thought it was the rear grommet that the reservoir was not completely seated in that was the culprit. That's what really threw me this morning after I finally got it to seat well last night. I suppose the telltale sign is if you have any level of fluid in the booster you have a MC that is on its way out?

I have a MC standing by from my parts car. The parts car is a manual so the little plastic stub piece is severed to allow fluid for the clutch. Anyone see any problems with using a short piece of hose, plugging and clamping the plug so that I have a seal and using it this way. I suppose I could steal the reservoir and grommets from my current MC I would just like to swap the complete unit to eliminate variables.

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