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Master cylinder leaking into vacuum booster, fluid being sucked into manifold.
R&R master cyl. Flush interior of booster with Brake Clean (If it's the type you can clean out) If the booster cannot be cleaned, you should probably replace it as the brake fluid will cause internal deterioration and eventual failure. Clean out all vacuum lines or replace as well. Brake fluid absorbs moisture, and can cause rust on metal, and deterioration of rubber components.
Gordon Raymond
 

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Why exactly would brake fluid damage a booster? I've had plenty of them filled with brake fluid, but haven't lost one yet. I just suction/wipe out the fluid and install the new MC. Seems like the rubber diaphragm would be just as resistant to brake fluid as the seals in the cylinders. What am I missing, anyone opened up a booster and seen a diaphragm damaged by the fluid?
 

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Seems like the rubber diaphragm would be just as resistant to brake fluid as the seals in the cylinders.
Seems like and actually being resistant are two different things. Who can really say that the diaphram was designed to be in contact with brakefliud?
Two other thoughts. One is that with fluid in the booster, part of the diaphram is being pushed against a vacuum while another part is being pushed against a liquid. Granted, the liquid won't cause the equivalent of hydraulic lock but the diaphram could eventually weaken due to non-uniformity of motion. The second thought is the resulting rust caused by the moisture in the brakefluid.
 

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Hmm, you might be right, Jim. Especially about the rust. As for the rubber, I can't imagine the manufacturers would use something that wasn't resistant to the effects of brake fluid (unless we're talking about English cars ;) ). I've got a nasty, rusted booster somewhere. I should open it up, cut a piece of the diaphragm out, and put it in a jar of brake fluid for a few years.
 

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Potential booster failure

I only had one diaphram fail, but that was enough. The MC rear seal leaked into the front section of the booster. This was a Ferrari booster, I believe a Girling, but I am no longer sure. I cleaned it out and could SEE :rolleyes:the rubber appeared fine, no cracking, or hardening. After reassembly, about 3 months later, the pedal became hard, then harder:confused:. The Ferrari Girling discs, weren't great to begin with. Real STOPPING was nearly impossible:eek:. Took it apaty again to find the still soft diaphram had a crack in the bottom of it where there still was some fluid:eek:. As this was an expensive booster replace, since that time I have always washed out the brake fluid with Brake Clean spray. Sometimes, there is rust in there too:p. I don't feel you can be too careful with any brake work on valuable cars;)! Good enough, may not be good enough, and the final result may be disaster:eek:. :DGordon Raymond
 
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