Master cylinder leaking at booster gasket. Could my brakes fail suddenly as a result?
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RWD 19xx-1984 DeVille and Fleetwood,
1985-1996 Fleetwood and Brougham Forum Discussion, Master cylinder leaking at booster gasket. Could my brakes fail suddenly as a result? in Past Cadillac Vehicle Discussion; My '79 DeVille has recently started leaking two streams of brake fluid between the master cylinder & power booster. I ...
  1. #1
    Benzilla's Avatar
    Benzilla is offline Cadillac Owners Connoisseur
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    Exclamation Master cylinder leaking at booster gasket. Could my brakes fail suddenly as a result?

    My '79 DeVille has recently started leaking two streams of brake fluid between the master cylinder & power booster. I first noticed it a couple months ago when I had new calipers, wheel cylinders & pads installed & the system bled. I just thought it was overflow from the bleeding. Yesterday I noticed it leaking, so I wiped it off, later drove it, & today went out to find the leak in full attendance.

    According to my research, it's likely a gasket problem, but I read somewhere that the fluid getting where it's not supposed to can weaken the brake booster, and possibly cause catastrophic failure unexpectedly while driving... is this true? I'm up at my parents' house, was planning on leaving today or tomorrow, but now I'm feeling uneasy about the 150 mile trip.

    Bottom line question: Could this problem cause my brakes to just go out & kill me on the way home, or will I be able to drive home safely & get it looked at later?

    Also, does this mean I should expect to replace my master cylinder + booster, or am I over reacting? This is another first for me

    Thanks!

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    outsider is offline Cadillac Owners Connoisseur
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    Re: Master cylinder leaking at booster gasket. Could my brakes fail suddenly as a res

    I don't know if it could cause the brakes to fail suddenly or not but how do the brakes feel?

    My main concern would be that you'd run out of fluid from the leak and then your brakes would fail (or rather, get very unresponsive)

    I, personally, would try to make it home. 150 miles isn't that far. I'd keep a bottle of brake fluid handy and give it a shot. If the brakes still feel good then I wouldn't be too worried about them just dying. But I've also driven my 95 with a blown brake line for like a week before getting it replaced...

    ----------

    As for what to replace...have you tried tightening the nuts that hold the master to the booster? give that a shot and see if your leak goes away. If not, get the gasket. Chances are if your brakes are feeling ok then your cylinder and booster are still good.

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    Re: Master cylinder leaking at booster gasket. Could my brakes fail suddenly as a res

    When the master cylinder leaks, it's usually the piston bore which is at the back of the MC where the rod for the brake pedal is. That's why it leaks between the MC and the booster. There's no gasket there to my knowledge.

    As long as you keep fluid in it, it should not cause a sudden failure. It's not something that's going to suddenly fail - it's just a worn bore. Eventually enough air will get in there that it will affect braking even when the fluid is full.

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    j2rossit is offline Cadillac Owners Enthusiast
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    Re: Master cylinder leaking at booster gasket. Could my brakes fail suddenly as a res

    A leak between the MC and the booster means the MC is bad. There is no gasket, it is a seal that the MC piston has. You might be able to replace the seal, but they are cheap enough that I'd just replace the whole unit (you would need to rebleed the brakes anyway). If the brake fluid spends enough time on the booster, it might (but I don't know for sure) cause a vacuum leak which would kill your power breaks (think of how your brakes feel if you move the car around without the engine running, that is how it feels if the booster fails).
    Boosters are expensive and can be replaced without needing to re-bleed the system, so I might be inclined to inspect the booster you have to see how it is. If the booster starts failing, you'll probably hear a hissing noise when you touch the brake pedal.

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    Re: Master cylinder leaking at booster gasket. Could my brakes fail suddenly as a res

    I might limp it home, if the drive requires very little braking. HOWEVER, a leak before the prop valve means if you lose fluid, you can have no brakes at both ends. If you have time, change it out before you leave.

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    Re: Master cylinder leaking at booster gasket. Could my brakes fail suddenly as a res

    Thanks guys! As for brake feel, I've had an ongoing complaint that the pedal seems to engage lower than it should, but I haven't experienced any fade-away while they're applied, that I've noticed. About a week ago, I was stuck in traffic & had to idle mostly with the brakes applied for about 15-20 minutes, facing slightly downhill, and they didn't fade then. Is it possible for the leak to get rapidly worse to where I wouldn't be able to keep up with the fluid during the trip?

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    jamespowers is offline Cadillac Owners Connoisseur
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    Re: Master cylinder leaking at booster gasket. Could my brakes fail suddenly as a res

    Quote Originally Posted by Benzilla View Post
    Is it possible for the leak to get rapidly worse to where I wouldn't be able to keep up with the fluid during the trip?
    Now you are getting me into the what ifs here. I have had problems with my 75 Eldorado's brakes in a similar vein. I think if I were stuck 150 miles from home with the same problem I would likely find a way to stop the leak. This doesn't mean I would take it to a mechanic though. I would find a stop gap method that might work. Right now, I am thinking that I might go for the plumber's putty and stop the leak with that by sealing the area where the master meets the booster. I have no idea if it would work or for how long but it is what I think I might try. Then again, you always have your foot brake if that goes out. That might take a bit of getting used to for a long trip though.

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    Re: Master cylinder leaking at booster gasket. Could my brakes fail suddenly as a res

    The issue isn't where the master meets the booster. There's no fluid seal there. All you'd do by sealing that up is force more fluid into the booster which is worse. The master cylinder is bad and needs replaced. It has everything to do with the brake pedal travel issue you've been experiencing. It will likely be fine until you get home, but I would replace it as soon as you can.

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    Re: Master cylinder leaking at booster gasket. Could my brakes fail suddenly as a res

    Also, if your e brake doesn't work really well, don't even think about driving it home.

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    Re: Master cylinder leaking at booster gasket. Could my brakes fail suddenly as a res

    A well bench bled master cylinder replacement requires no additional brake bleeding. This was the normal way to replace master cylinders back in the day.

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    A friend of mine (who isn't the smartest car wise) drove for over a month with a bad MC in his roadmaster. I drove it, and pushing the pedal hard (like you would in a panic stop) was equal to lightly pushing the brakes. I would not advise driving with a bad MC (especially if you have to stop alot), but it is doable.

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    Re: Master cylinder leaking at booster gasket. Could my brakes fail suddenly as a res

    Quote Originally Posted by cadillac kevin View Post
    A friend of mine (who isn't the smartest car wise) drove for over a month with a bad MC in his roadmaster. I drove it, and pushing the pedal hard (like you would in a panic stop) was equal to lightly pushing the brakes. I would not advise driving with a bad MC (especially if you have to stop alot), but it is doable.
    Why is all this reminding me of the scenes in Fletch Lives where his 59 Cadillac doesn't have brakes so he ends up running into things to stop? Parking meters for instance:
    i087701.jpg

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    Re: Master cylinder leaking at booster gasket. Could my brakes fail suddenly as a res

    My e-brake cable is snapped so I don't have a back up plan. Driving out to Vermont I was eyeing up those runaway truck ramps and wondering whether I would ever need them. Turned out the transmission failed and going was the problem - not stopping.

    Thankfully I've never had to purposely ram an inanimate object to get my car stopped. I've involuntarily done it, though. Word to the wise - trees stop you FAST. They may be all green and pretty but there's not much give there. Telephone poles have a bit more give, but not a lot. I would avoid both trees and telephone poles as a means to slow a Fleetwood down. Just sayin.

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    jamespowers is offline Cadillac Owners Connoisseur
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    Re: Master cylinder leaking at booster gasket. Could my brakes fail suddenly as a res

    Quote Originally Posted by turbojimmy View Post
    My e-brake cable is snapped so I don't have a back up plan. Driving out to Vermont I was eyeing up those runaway truck ramps and wondering whether I would ever need them. Turned out the transmission failed and going was the problem - not stopping.

    Thankfully I've never had to purposely ram an inanimate object to get my car stopped. I've involuntarily done it, though. Word to the wise - trees stop you FAST. They may be all green and pretty but there's not much give there. Telephone poles have a bit more give, but not a lot. I would avoid both trees and telephone poles as a means to slow a Fleetwood down. Just sayin.
    The emergency brake cable would be the first thing I would fix if mine broke. I saved myself a few times with different cars due to them. One being a 55 Chevy and another a 57 Chevy. No brakes, no problem----we have a hand brake. You have to be really coordinated to do this for long distances though.

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    Re: Master cylinder leaking at booster gasket. Could my brakes fail suddenly as a res

    E brakes were REALLY important back in the single res MC days (pre-67).

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