: Master cylinder leaking at booster gasket. Could my brakes fail suddenly as a result?



Benzilla
06-04-13, 01:47 PM
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!

outsider
06-04-13, 01:56 PM
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...

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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.

turbojimmy
06-04-13, 02:09 PM
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.

j2rossit
06-04-13, 02:32 PM
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.

jayoldschool
06-04-13, 02:33 PM
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.

Benzilla
06-04-13, 02:50 PM
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?

jamespowers
06-04-13, 03:52 PM
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. :p 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. :p

turbojimmy
06-04-13, 04:13 PM
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.

jayoldschool
06-04-13, 06:26 PM
Also, if your e brake doesn't work really well, don't even think about driving it home.

The Ape Man
06-04-13, 06:52 PM
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.

cadillac kevin
06-04-13, 07:33 PM
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.

jamespowers
06-04-13, 07:42 PM
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? :p Parking meters for instance:
113449

turbojimmy
06-04-13, 08:22 PM
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.

jamespowers
06-04-13, 08:36 PM
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. :p 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. :p You have to be really coordinated to do this for long distances though. :p

jayoldschool
06-04-13, 09:22 PM
E brakes were REALLY important back in the single res MC days (pre-67).

jamespowers
06-04-13, 09:54 PM
E brakes were REALLY important back in the single res MC days (pre-67).

I had power brakes on the 55. :p They are still important even today if your brakes go out. :p

Benzilla
06-04-13, 10:45 PM
Thanks for all the advice. I decided to move some things around & get it fixed before I leave, there's a local shop that I trust (as much as any shop) here in town that I had my alignment done at. They were worried about finding parts, but I lucked out & found a Cardone master/booster combo & already picked it up. Going in tomorrow.

jayoldschool
06-04-13, 11:09 PM
Good call, Ben.

turbojimmy
06-05-13, 07:54 AM
The emergency brake cable would be the first thing I would fix if mine broke. :p 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. :p You have to be really coordinated to do this for long distances though. :p

Well, it's another one of those limo-specific things. The 5-foot extension installed by the coach builder snapped. I need a custom cable made up. I bought some cable and random fittings as a temporary fix but haven't had time to mess with it.

The Ape Man
06-05-13, 10:49 AM
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? :p Parking meters for instance:
113449

Back in the 80s I had a beater '76 CDV. Insurance was due to run out and I was putting a nice '77CDV back on the road and the car was going to be an engine donor. I used to slam into the dumpster at work every day on the way in. No brakes needed.

deVille33
06-05-13, 11:00 AM
I had to laugh at turbojimmy's description of his experience. Those truck ramps are filled with loose gravel and the vehicle that goes into one is supposed to sink into the gravel to stop it. It then has to be towed out of the trap by wreckers. I've used snow banks to stop some of my cars when needing emergency measures. A friend once used those old pillar type guard rails. They do a lot of damage to the car.:)

jayoldschool
06-05-13, 11:48 AM
When the brakes failed on my 87 Caprice (line broke before the prop valve), I used a Tercel to stop. I was going about 45, the Tercel was not. It wasn't pretty for the Tercel.

jamespowers
06-05-13, 12:05 PM
Well, it's another one of those limo-specific things. The 5-foot extension installed by the coach builder snapped. I need a custom cable made up. I bought some cable and random fittings as a temporary fix but haven't had time to mess with it.

Gee, if you were out here I would have a guy I know make you one. He is at a place called California Push Pull. He would be able to knock one out in about twenty minutes. :p

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Back in the 80s I had a beater '76 CDV. Insurance was due to run out and I was putting a nice '77CDV back on the road and the car was going to be an engine donor. I used to slam into the dumpster at work every day on the way in. No brakes needed.

A friend of mine stopped his Mustang with fifty feet of fence, a VW bug and ultimately a telephone pole when he dropped the linkage one time. :p He only got a cut on his arm doing all that. The VW lost its rear end. :p

Benzilla
06-05-13, 11:18 PM
Done. My shop said it was a PITA to get it changed, but that did it pretty fast. I can tell a difference in braking already, they're more springy & responsive. (I still think the pedal could start grabbing higher, but I think ApeMan on here said that was a design flaw of sorts in '79?) Also, I didn't realize how bad my pedal return was until the new master cylinder & power booster... Now the pedal almost chases my foot back up, before there was a good delay, not enough to catch my attention, but it wasn't snappy. Glad to cross that off the list! I'll have to link back to this when I get the consolidated thread for my Phaeton started.

:)

72DeVilleCT
06-06-13, 04:42 PM
I the same thing, it went on for some time but the brakes did fail, and fail BIG! I would fix this ASAP. No breaks in a Cadillac is literally a runaway train.

83 Fleetwood
06-06-13, 07:29 PM
I have blown the brake lines on my caddy and glad it happened at my ex-wife's house when it did, and not on the highway. The only brakes I had left was the e-brake and it was interesting loading the car onto the trailer to tow it to say the least.

Get it fixed asap would be my recommendation

James