Brake Problem Help Needed
Thread Starter
Instructor
Joined: Jan 2006
Posts: 165
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From: Richmond Tx
Brake Problem Help Needed
I have a brake issue that is driving me nuts. Driving along the brakes start applying by themselves and by the time I get stopped, the pedal is rock hard. Sit for 30 minutes and pedal releases and I can drive on sometimes for 50 miles. All of the calipers have been changed along with the master cylinder and rubber lines.
Any suggestions on where to look? Thanks
Any suggestions on where to look? Thanks
Thread Starter
Instructor
Joined: Jan 2006
Posts: 165
Likes: 0
From: Richmond Tx
I did some test. Drove applying brakes often until started to lock up. Temp gun on rotors, and the rears where 50 deg. hotter. Must be the rears causing the problem. Could the problem be with the proportional valve??? Brake fluid getting hot and locking the system down? Just chime in if you can. Thanks
Drifting
Joined: Apr 2004
Posts: 1,651
Likes: 11
From: Seattle WA
Originally Posted by Higs
I did some test. Drove applying brakes often until started to lock up. Temp gun on rotors, and the rears where 50 deg. hotter. Must be the rears causing the problem. Could the problem be with the proportional valve??? Brake fluid getting hot and locking the system down? Just chime in if you can. Thanks
I had to have a new rotor and another new caliper. Not fun.
Good luck
Tech Contributor
Joined: Aug 1999
Posts: 15,116
Likes: 3,911
From: Connecticut, USA
You have an issue to deal with and I would start from the beginning. Sounds like a rubber hose is swollen and locking a caliper, coul dbe a stuck piston too if the car sat for a while. I would look over the system, something is wrong, are you sure you have the correct M/C?
Thread Starter
Instructor
Joined: Jan 2006
Posts: 165
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From: Richmond Tx
I had this problem last weekend for the first time. I had changed the front calipers a month ago and the rears were fairly new when I got the car. That is why I replaced both rear calipers and the rubber lines this morning and bled them really good to remove alot of the old fluid that might have gotten hot last weekend. Something is causing an expansion or not releasing the rears. Thanks for the comments.
Le Mans Master
Joined: Mar 2001
Posts: 6,638
Likes: 287
From: Ann Arbor Michigan
One more thing to look at is the Master Cylinder. If the pushrod is holding the M/C piston partically in, and covering the compensation port, then the fluid will not return from the caliper to the M/C as it heats up and expands. The quick way to check this is to crack one/both of the brake lines at the M/C when the brakes are locked up. If they don't release, then it's somewhere else as others have suggested.
Melting Slicks
Joined: Dec 2000
Posts: 3,407
Likes: 2
From: Carmichael CA
The heat may be coming from another source. I had the same problem and it was the rear spindles due to the lack of lubrication in the rear bearings causing the heat which in turn made it feel like the brakes were being applied...the pedal also felt stiff probably due to the brake fluid getting heated up. A spindle finally snapped...it wasn't pretty.
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Thread Starter
Instructor
Joined: Jan 2006
Posts: 165
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From: Richmond Tx
I can drive it all day long with no problems as long as I dont use the brakes so I don't think it is the rear bearings. Something is causing the rear calipers to not release and then the heat builds up from there. Are there any other rubber lines other than the short ones by the calipers that might be swelling? By the way, this is on an 80.
Le Mans Master
Joined: Mar 2001
Posts: 6,638
Likes: 287
From: Ann Arbor Michigan
Originally Posted by Higs
I can drive it all day long with no problems as long as I dont use the brakes so I don't think it is the rear bearings. Something is causing the rear calipers to not release and then the heat builds up from there. Are there any other rubber lines other than the short ones by the calipers that might be swelling? By the way, this is on an 80.
Thread Starter
Instructor
Joined: Jan 2006
Posts: 165
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From: Richmond Tx
The MC is new and only been on a couple of months. The problem is I can't figure out what is starting the sequence of lock up. In the garage, everything looks fine. Bleed process goes smooth etc... I will re-check that fulid is returning to MC when bleeders closed. Something is wack and I WILL FIND IT! Thanks for the input folks.
Burning Brakes
Joined: Feb 2002
Posts: 752
Likes: 31
From: Melbourne Australia
What was the outcome?
I just looked at a 74 with the same problem! The pushrod was adjusted wrong after a M/C replacement...about 3/16" too long. I'm thinking that not allowing the piston to return completely will allow pressure to build up in the fluid. I just sent the owner home after I adjusted it properly...we'll see if that fixed it. Duke94 had the same idea earlier in this thread.
Did you get to the bottom of your problem?? I'd like to know how you fixed it.
Cheers,
Joe
Did you get to the bottom of your problem?? I'd like to know how you fixed it.
Cheers,
Joe
Burning Brakes
Joined: Oct 2004
Posts: 763
Likes: 0
From: Loveland Colo
Just throwing out a couple thoughts here... Have you tried cracking a bleeder valve when it's locked up to see if the lines are pressurized? Or checking the master cylinder fluid level to see if any change in level between free and locked up? Did you bench bleed the master cylinder prior to installation? Engine compartment lines heating from proximity to headers, etc?
(I had a brake sieze one time on my bike when I came from SoCal at sea level up to Colorado at a mile high due to a bit of air which expanded from the change in atmospheric pressure. Master cylinder level came way up, but once I relieved the pressure, all was OK till I could re-bleed.)
Perhaps a drum brake master cylinder with a check valve instead of a disc brake unit with no check valve? I never thought about this as pertaining to my car, don't know that it does, but it is a source of problems for those who convert the old Harley drums to disc...
John
(I had a brake sieze one time on my bike when I came from SoCal at sea level up to Colorado at a mile high due to a bit of air which expanded from the change in atmospheric pressure. Master cylinder level came way up, but once I relieved the pressure, all was OK till I could re-bleed.)
Perhaps a drum brake master cylinder with a check valve instead of a disc brake unit with no check valve? I never thought about this as pertaining to my car, don't know that it does, but it is a source of problems for those who convert the old Harley drums to disc...
John
Burning Brakes
Joined: Feb 2002
Posts: 752
Likes: 31
From: Melbourne Australia
John,
Interesting thought about the drum brake M/C with the one way valves......
In any case, adjusting the M/C push rod correctly, fixed the problem in the 74. It seems that the brakes unlocked once the nuts on the M/C were backed off allowing the M/C to move forward and the piston to return fully. This suggests the fluid return port was not being opened because the piston did not return far enough.
Cheers,
Joe
Interesting thought about the drum brake M/C with the one way valves......
In any case, adjusting the M/C push rod correctly, fixed the problem in the 74. It seems that the brakes unlocked once the nuts on the M/C were backed off allowing the M/C to move forward and the piston to return fully. This suggests the fluid return port was not being opened because the piston did not return far enough.
Cheers,
Joe
