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Old 06-26-2017, 12:50 PM
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Sudden brake failure

While driving yesterday the brake pedal unexpectedly went down to the floor when pressure was applied. I could get the brakes to work poorly if I vigorously pumped the pedal. I managed to limp home. Where should I look first? The reservoir is completely full. I checked the vacuum hoses where I could access them from above and all look ok. I would like to get the brakes working even a little bit to drive to the mechanic and save the tow fees. Any suggestions?
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Old 06-26-2017, 12:55 PM
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I wouldn't risk driving it with inefficient brakes. Even a low speed crash would cost more in repairs than the fees for a tow. And if a child ran out in front you suddenly...
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Old 06-26-2017, 01:03 PM
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Quote:
Originally Posted by Temerian View Post
While driving yesterday the brake pedal unexpectedly went down to the floor when pressure was applied. I could get the brakes to work poorly if I vigorously pumped the pedal. I managed to limp home. Where should I look first? The reservoir is completely full. I checked the vacuum hoses where I could access them from above and all look ok. I would like to get the brakes working even a little bit to drive to the mechanic and save the tow fees. Any suggestions?
Brake Booster
Master Cyl
Fluid leaking from any of the brake calipers themselves?

The risk vs the reward isn't worth it IMO, you don't know what you don't know and a transporter will be way less than an insurance claim.

Please be careful!

S
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Old 06-26-2017, 01:04 PM
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You are right, Ewan. It's probably not worth the risk. I thought there might be a simple fix.
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Old 06-26-2017, 01:32 PM
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Definitely check for leaks at each caliper and inspect all lines, hoses, etc...

If fluid level is good and no leaks, a seal may have failed in your master cylinder.
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Old 06-26-2017, 06:05 PM
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Rick....first, it's not worth the risk...call a flatbed truck. OK ?

Second...The brake system is a "closed" hydraulic system, if you push the pedal down to the floor with no or little resistance, one of two things is at fault.

Either you are "pumping" brake fluid out on the floor thru a leaking hose, pipe or caliper seal.....(but you say there is no change in the fluid level at the reservoir).....or.....you are "bypassing" fluid from the compression chamber in the master cylinder past a split or broken seal, to behind the seal where the fluid can return to the reservoir.
If you were seeing the reservoir fluid go down, I would also check the joint between the reservoir & the m/cylinder for leakage, or even the carpet inside since it is possible to have fluid leak thru the booster also.

It sounds like your master cylinder is at fault, if it is not scored or scratched inside, it can be easily rebuilt.

Gary

PS: I already have a kit here for mine, full brake job is on my list of things to do.
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Old 06-26-2017, 08:35 PM
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It should have a dual circuit to every wheel so that if something fails you still have braking on every wheel. If you have lost both circuits I would suspect the master cylinder has had moisture in it for some time and the whole system will need an overhaul.
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Old 06-26-2017, 09:56 PM
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Correct, Al. The system is a true dual circuit. I agree that its the master cylinder not building pressure.
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Old 07-13-2017, 09:54 AM
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So what was the verdict on the failure?
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Old 07-13-2017, 12:53 PM
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A vacuum hose rupture. Replaced the hose and it's working fine. I'm going to replace all the belts and hoses now just to reduce the number of things that can fail.
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Old 07-13-2017, 03:02 PM
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A leaking vacuum hose will cause the brake pedal to be very hard to push in but cannot cause the symptoms you described. I hope you don't find out the hard way that this was not the cause of the pedal going to the floor.
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Old 07-13-2017, 04:13 PM
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A leaking vacuum hose will cause the brake pedal to be very hard to push in but cannot cause the symptoms you described. I hope you don't find out the hard way that this was not the cause of the pedal going to the floor.
Correct. Could be a bad master cylinder.
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Old 07-13-2017, 05:14 PM
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You are correct, Al. I mis-described the symptoms. The pedal was super hard to push but it would stop the car.
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Old 07-13-2017, 07:20 PM
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If the system is similar to my Rolls ('67 Shadow), there is no "master cylinder" or vacuum brake booster.
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Old 07-13-2017, 07:47 PM
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Glad you found it and a simple fix. Good call on replacing the other stuff!
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  #16  
Old 07-15-2017, 03:44 PM
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Originally Posted by kevfla View Post
If the system is similar to my Rolls ('67 Shadow), there is no "master cylinder" or vacuum brake booster.
This post made me curious so I investigated. Good Lord, talk about needless complication.
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Old 07-15-2017, 06:26 PM
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Back in 1994 when I bought a 1985 Maserati Biturbo while I was still only 20 years old, I joined AAA before going to pick it up. 23 years later, I am still a member. For like $75-$90.00 per year on the gold membership, you have up to 4 tows per year, up to 100 miles each! Throughout the years, I will run out of my 4, and then get a card for the ex to use up her allotted tows at whatever price the membership comes out pro rata 6+ plus months in.

Trust me, its worth it. I just used my 3rd tow on Friday as of March and have peace of mind.
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Old 07-16-2017, 11:47 AM
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A vacuum failure is unnerving, a failed master is nerve wrecking. I experienced both (yes on a dual system) and ever since I have a master overhaul on every car's maintenance list (apart from 36 month maximum fluid changes).
One overhaul or replacement every two decades or so costs peanuts and believe me, it's very much worth it.
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Old 07-16-2017, 04:45 PM
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[QUOTE=OttoB;145478963]
Back in 1994 when I bought a 1985 Maserati Biturbo while I was still only 20 years old, I joined AAA before going to pick it up. QUOTE]

Sounds like you knew what you were in for.
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  #20  
Old 07-17-2017, 10:47 AM
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Some bad news. Going through the coolant system we found engine oil in the radiator.
Looks like I'm going to have to pull the motor. Any advice other than expect to spend a lot of money?
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