Brake problem.
Thread Starter
Pro
Joined: Jul 2004
Posts: 639
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From: 1985 L98, Auto. O'FALLON, IL
Brake problem.
I had to slam on the brakes yesterday for a deer and when I did I heard a pop and the pedal went about 3-4 inches farther down before the brakes worked. I did a good physical inspection today and don't see anything obvious. When the engine is not running the pedal pumps up hard but when started the pedal moves down about 3 inches. Is this a bad booster or would it be the master cylinder? Thanks for any help.
Melting Slicks
Joined: Apr 2003
Posts: 3,110
Likes: 6
From: Red Sox Nation! RI
I've never heard that one before, but it sounds like your booster. The pop you heard may have been the diaphragm in the booster. And since you lose your pedal when the car is running, that would indicate the booster isn't holding vacuum for power assist.....that's my guess, anyway.
If the master is bad, it will be leaking around the mounting flange.
If the master is bad, it will be leaking around the mounting flange.
Instructor
Joined: Jun 2006
Posts: 194
Likes: 0
From: Hartselle Al
I have cracked a pad on my old standard brakes. The pedal went another inch to the floor. Also in a old jeep, I got a similar feeling from a master cylinder that leaked all pressure out the back, that left a fluid trail to follow; easy to see. In a Ford/ excuse me, in a Mercury Grand Marquees, I had a metal line blow out, yes, metal, it was rusted and a chunk came off, Yankee car from my grandparents. So, Look for fluid first, look real close near the master cylinder to booster. Check the vacuum hoses. Then look at the pads and calipers.
I hate brakes…
I hate brakes…
Le Mans Master
Joined: Jan 2006
Posts: 5,621
Likes: 206
From: Orlando FL
I would first inspect under the dash and just check the pedal assembly, rod connection and such to make sure it looks normal.
Popping the diaphragm in the booster is not likely because you would not be able to press the pedal as far as you can. There would be a hard pedal and no almost brakes. And there would be a Hugh vacuum leak and engine idle would be high probably. I wouldn’t think you could do anything to the calipers. If you blew a flex line that would be obvious.
I would pull back the master and inspect that real carefully. Check the rod from the booster for any damage, bending or shortness. I think this area is the highest probably of seeing something.
Popping the diaphragm in the booster is not likely because you would not be able to press the pedal as far as you can. There would be a hard pedal and no almost brakes. And there would be a Hugh vacuum leak and engine idle would be high probably. I wouldn’t think you could do anything to the calipers. If you blew a flex line that would be obvious.
I would pull back the master and inspect that real carefully. Check the rod from the booster for any damage, bending or shortness. I think this area is the highest probably of seeing something.
Instructor
Joined: Jun 2003
Posts: 151
Likes: 1
From: Newark CA
It most likely is not the booster for reason stated above. When the booster goes out the pedal becomes hard, but looses stopping power. Check for fluid leaks, at all 4 corners as well as the master cylinder. Is it making noise while braking?
Le Mans Master
Joined: Sep 2006
Posts: 6,050
Likes: 147
From: Phoenix AZ
2021 C4 of the Year - Modified Finalist
booster
ok..
got vice grips? make 2 little pieces of flat metal and place them on the booster vacuum hose. squeeze them with vice grips and make the hose flat so no vacuum will go to your booster. not too tight, just enough.
don't try taking off the hose, you will just mess up everything.
pump the brakes till the pedal is hard.
drive the car up and down the street. don't go anywhere. is the pedal different?
now take off the vice grips. go up and down the street. pedal different?
if the pedal is different, easier, your booster is working.
If theres no change, you need a booster.
now 2 things...
1, there is a brake bias spring inside the piston in yoiur master cylinder. without really hard stops, this little piston attached to the spring can get stuck, and you could have popped it loose.
2. there is a possibility you could have energized your ABS, and it only relieved once.
try the vice grips first. the master cylinder repair kit is exxpennnsive
got vice grips? make 2 little pieces of flat metal and place them on the booster vacuum hose. squeeze them with vice grips and make the hose flat so no vacuum will go to your booster. not too tight, just enough.
don't try taking off the hose, you will just mess up everything.
pump the brakes till the pedal is hard.
drive the car up and down the street. don't go anywhere. is the pedal different?
now take off the vice grips. go up and down the street. pedal different?
if the pedal is different, easier, your booster is working.
If theres no change, you need a booster.
now 2 things...
1, there is a brake bias spring inside the piston in yoiur master cylinder. without really hard stops, this little piston attached to the spring can get stuck, and you could have popped it loose.
2. there is a possibility you could have energized your ABS, and it only relieved once.
try the vice grips first. the master cylinder repair kit is exxpennnsive
