Suddenly soft brakes
Thread Starter
Burning Brakes
Joined: Jan 2006
Posts: 1,223
Likes: 174
From: Fort Wayne IN
Suddenly soft brakes
I was taking my 76 with power brakes out a few nights ago, about 2 miles from home I notice my BRAKES light on. First thing I do is pull the parking brake up a notch and let it back down. Didn't go out. So I cautiously press on the brakes a few times and they get softer with every press, but still have some brake power. With a little downshifting I make it home fine. Once I get it back in the garage, I pop the master cylinder cover and shockingly it is full of fluid. I look under the car, no drips. I have my wife hold the brake to the floor, no leaks. Proportioning valve is dry too.
So if I had a firm pedal before I left, what would make it suddenly go squishy? I have not re-bled them yet, but if there is air in the lines now, where did it come from?
So if I had a firm pedal before I left, what would make it suddenly go squishy? I have not re-bled them yet, but if there is air in the lines now, where did it come from?
Melting Slicks
Joined: Feb 2003
Posts: 3,053
Likes: 4
St. Jude Donor '03,'11
when you press the brake do you slowly lose pedal like there is a leak? If so the master is bad. You won't see any external leak because the fluid is just bypassing the seals internally.
Race Director
Joined: May 2006
Posts: 16,528
Likes: 53
From: Dayton, Ohio
Melting Slicks
Joined: Feb 2003
Posts: 3,053
Likes: 4
St. Jude Donor '03,'11
yea, you have one circuit putting out pressure and the brake fluid leaking past the plunger on the other circuit causing a differential pressure in the switch.
I'm pretty sure i've experiened that before. I've toasted everything on my car in about everyway possible over 30 years.
it could very well be what you suggested first. just another possibiltiy. easiest thing is to bleed the brakes first as you suggested.
I'm pretty sure i've experiened that before. I've toasted everything on my car in about everyway possible over 30 years.
it could very well be what you suggested first. just another possibiltiy. easiest thing is to bleed the brakes first as you suggested.
Last edited by turtlevette; Jul 21, 2010 at 09:35 PM.
Advanced
Joined: Oct 2007
Posts: 59
Likes: 0
My master went just a week after I replaced the calipers. Looked for a leak and bleed the system for hours........replaced the master and problem was solved.
Instructor
Joined: Jun 2010
Posts: 199
Likes: 0
had the same issue mine was the left rear sucking in air into the system. there was a very lil tiny spot where it was leaking when breaks applied i mean really tiny. but it was enough to suck air into the system and my breaks got real squishy. i had to drive home with the E-brake oh that was fun 
.
Found it when i tried bleeding the brakes that my left rear was empty.
. Found it when i tried bleeding the brakes that my left rear was empty.
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Race Director
Joined: May 2006
Posts: 16,528
Likes: 53
From: Dayton, Ohio
I would also bet(but only a dollar)that the RR will be the culprit.
Good Luck and I hope this isn't the start of a body off.
Former Vendor
Joined: Nov 2006
Posts: 2,482
Likes: 3
From: Carmichael ca
If you do find air in one of the rear calipers, check for play in the wheel bearing. I've seen wobbly bearings cause this problem. If there is no air try gently pushing on the brake pedal. If it slowly sinks that's a bad master cylinder.
Le Mans Master
Joined: Oct 2000
Posts: 8,897
Likes: 1,356
From: Santa Ana CA
Sounds like "air pumping" through the rotors due to excessive runout (been there, done that, and lost my brakes on the freeway 
).
Re-bleed all the brakes and take it up on the road for a cruise. If the problem returns, have the rotors checked for runout.
).Re-bleed all the brakes and take it up on the road for a cruise. If the problem returns, have the rotors checked for runout.
