Brakes keep locking down!
Thread Starter
Instructor
Joined: May 2006
Posts: 181
Likes: 0
From: Atlanta GA
Brakes keep locking down!
Hey Everyone,
First off, let me say thanks to everyone here for helping me get my first project car on the road. Now that it is on the road though, it keeps stopping! The rear brakes progressivly "lock-down" under normal driving conditions, and the only way to get the car rolling again is to bleed the rear at the master cylinder. Originally it was locking down on all four corners, but as I've changed the different parts, the rear continue to do so. Talk about frustrating, finally get the car ready to go, but it won't let me, haha. Here's what I've done so far:
1. New front calipers & pads
2. New master cylinder
3. New proportioning valve
The reason I haven't replaced the rear calipers is because they "appeared" new when I bought the car last June. My questions is, should I just go ahead with new rear calipers, or does the problem seem to lie in the brake lines themselves? Thanks for the help in advance!
First off, let me say thanks to everyone here for helping me get my first project car on the road. Now that it is on the road though, it keeps stopping! The rear brakes progressivly "lock-down" under normal driving conditions, and the only way to get the car rolling again is to bleed the rear at the master cylinder. Originally it was locking down on all four corners, but as I've changed the different parts, the rear continue to do so. Talk about frustrating, finally get the car ready to go, but it won't let me, haha. Here's what I've done so far:
1. New front calipers & pads
2. New master cylinder
3. New proportioning valve
The reason I haven't replaced the rear calipers is because they "appeared" new when I bought the car last June. My questions is, should I just go ahead with new rear calipers, or does the problem seem to lie in the brake lines themselves? Thanks for the help in advance!
Team Owner
Joined: Jul 1999
Posts: 65,492
Likes: 230
From: Orange Park Florida
I would suspect that both rear hoses would not be locking up but just one end...with posi, it would be hard to tell, number one, and releasing the pressure at the m/cyl would cure the problem....AND....
I had the exact same problem with my driver's front caliper.....burnt the damn thing up by time I was able to get home....an O ring rebuild kit from VBP as they were O ringed years ago....and a new hose for both sides from down the street, and they are good to go....again....
damn hose can lock up internally from rot and pass super pressure, but will not release the pads/shoes/whatever......not so long ago I had the same thing on my work van...Dodge 3/4 ton...on the pass side.....
cant win....
I had the exact same problem with my driver's front caliper.....burnt the damn thing up by time I was able to get home....an O ring rebuild kit from VBP as they were O ringed years ago....and a new hose for both sides from down the street, and they are good to go....again....
damn hose can lock up internally from rot and pass super pressure, but will not release the pads/shoes/whatever......not so long ago I had the same thing on my work van...Dodge 3/4 ton...on the pass side.....
cant win....
Race Director
Joined: Sep 1999
Posts: 11,361
Likes: 383
From: Plano TX
Your master is not being allowed to return to the "at rest" position. If you have power brakes, the most common cause is a pushrod that is adjusted too long. Also check your brake light switch in case it doesn't let the pedal all the way up.
Easy check: With engine off, remove reservoir cap. Push pedal down and then slowly up. Right before it is released all the way there should be a squirt in each reservoir when the master opens the passages. Rags are recommended as fluid can squirt out of the reservoir.
Easy check: With engine off, remove reservoir cap. Push pedal down and then slowly up. Right before it is released all the way there should be a squirt in each reservoir when the master opens the passages. Rags are recommended as fluid can squirt out of the reservoir.
Racer
Joined: Aug 2006
Posts: 330
Likes: 3
From: Wellington, New Zealand
I had the same problem with the right rear on my 74, I replaced the pads and the problem went away but I suspect that the flexi hose was the problem and the act of compressing the pistons to fit the new pads dislodged any junk or loose rubber that was acting as a stop valve. I have now replaced the rear flexi lines and I must say the brakes have improved greatly and I would recomend swapping all flexi lines. By the way I have non power brakes
Instructor
Joined: Feb 2005
Posts: 134
Likes: 5
From: North Ga
Verify you have the correct master cylinder. I had a shop change my master cylinder and they put one on that was made for a front disc rear drum car. The correct one for your vette should have roughly equal size front/rear reservoirs the incorrect one that was installed on my car had a small oval front reservoir and a large rectangular rear reservoir.
Could be the parts store gave you the wrong one.
Could be the parts store gave you the wrong one.
Burning Brakes
Joined: Oct 2006
Posts: 1,006
Likes: 28
From: Lutz Florida
Your master is not being allowed to return to the "at rest" position. If you have power brakes, the most common cause is a pushrod that is adjusted too long. Also check your brake light switch in case it doesn't let the pedal all the way up.
Easy check: With engine off, remove reservoir cap. Push pedal down and then slowly up. Right before it is released all the way there should be a squirt in each reservoir when the master opens the passages. Rags are recommended as fluid can squirt out of the reservoir.
Easy check: With engine off, remove reservoir cap. Push pedal down and then slowly up. Right before it is released all the way there should be a squirt in each reservoir when the master opens the passages. Rags are recommended as fluid can squirt out of the reservoir.
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Thread Starter
Instructor
Joined: May 2006
Posts: 181
Likes: 0
From: Atlanta GA
Thanks everyone for the help. I forgot to mention, but it is power brakes. As far as the new master cylinder goes, it was the correct one from Autozone, with the same size front and rear. Also, I did bench-bleed the brakes in case that might be an issue. I will check the push-rod length when I get home from school. Is there any particular length it should be? Just wrenches to adjust it? Also, are the flex hoses just the normal brake lines? Thanks again!
Racer
Joined: Aug 2006
Posts: 330
Likes: 3
From: Wellington, New Zealand
The flexi lines are just the rubber ones, the hard lines (metal) should be fine. Good luck with it, a lot of people have problems bleeding corvette systems I have tried a lot of the fancy gear and found it useless, pedal pumping and gravity have always worked well for me.
Burning Brakes
Joined: Dec 2004
Posts: 918
Likes: 5
From: Gainesville FL
I second (third?) checking the flex lines. These were exactly the same symptoms on a friend's 75. Turned out that his rear flex lines were partially collapsed, even though they looked fine on the outside.
Thread Starter
Instructor
Joined: May 2006
Posts: 181
Likes: 0
From: Atlanta GA
Thanks again for the help. I wasn't able to check the rod-length last night, but will try today. After hearing it, the flexi lines make sense at being the cause of my problem. I guess I'll pick up a new set from Autozone or something. So far, I haven't had any problems bleeding the brakes on the car, I've just been doing it the same way as I do on my racecars, with a person pumping the pedal and me opening and closing the line on all four coners. Thanks again!
Le Mans Master
Joined: Mar 2004
Posts: 7,500
Likes: 1,508
From: Little Rock AR
If the master cylinder is not releasing the brakes because the pushrod adjustment is too long, you could just back off the mounting nuts to verify. If you back off the 4 mounting nuts on the M/C and the pressure releases on the calipers, you probably need to shorten the pushrod adjustment.
-Mark.
-Mark.
