first thing,the car has a standard corvete master power booster setup with disc brakes at all 4 wheels.on the cars first long outing ,driving to a club meeting.15 minutes on the freeway and the car starts getting "heavy",then it starts smelling like hot brakes,so I get off the road into a gas station.to let it cool down.i walk around the car and notice brake lights are on.which tells me there is pressure in the brake system,but i am out of the car...what gives?as it cools down,the brakes lights shut off.and the car brakes seem to have released.....what do u guys think is the problem..and starting the drive back home by street.i will check back in a while see what ideas u guys have as to what I should check.thnx in advance...
The push rod length is most likely too long holding the master cylinder too far down in the bore. Does this EVERY TIME...
Make sure the master is returning all the way. If the master is in a little it blocks the return hole in the master then holds presure witch get worse as brake fluid gets hot.
If the pushrod from the pedal to booster has the correct clearance and an effective return spring, the pushpin on the booster may be set too long, an easy way to check this is to loosen the two master mount bolts and slip body shims or slotted washers between the booster and the master and retighten them. If the problem is gone, you can go back and reset the pushpin.
Agreed. This is what caused the very same problem in my Corvette.It has an adjustment, shorten it a bit and try it again.
okay i will try shortening the pushrod length. question though. ive driven the car on the streets for the passed two weeks working out all the "mechanical bugs" and have not had this problem. but today that i get on the freeway, it does it? to me, would the brake system (fluid) get hotter when driving in the streets (idling at red lights) vs constant air flow on the freeway?
Have had this happen on a few cars as well-had to drive them a ways before brakes started dragging-neighbor had a Nomad that did this when built and only went about 3 miles before the front discs totally locked up-Rich B has the solution to try-I have done the same with shims to find the issue.
Yup! Happened to me once in my trusty ol 47 caddy. Rebuilt the master cylinder and re-adjusted the pushrod because it was a little sloppy...ran around town for about a week before I took a trip to Portland, oregon...an 85 mile trip. By the time I'd reached portland, my brakes were stinking and dragging. Slid under the car with an end wrench and adjusted a little more slack into the pushrod...instant fix! Make sure your return spring is bringing your pedal/pushrod all the way back and keeping it back while driving.
"notice brake lights are on"......what activates your brake light switch and/or where is it mounted ?? If it is mounted under the dash, and it is the plunger style, it may be misadjusted so that it is holding very slight pressure on the brake pedal arm.....the slight pressure will cause the brake pedal to depress the pedal rod into the master cylinder......the slight brake drag will heat up the calipers and increase pressure slightly.....adding more brake drag in a vicious cirlce. This was a problem on many "stock" GM vehicles for years.....including Corvettes.
I've had air in the lines at the calipers, calipers get warm and air expands and brakes come on by themselves the more you drive...
My buddy replaced the M/CL on his 64 Ford and after a few miles to a show, the same thing happened. We added washers between the firewall and the M/CYL to get it home. We were sitting in it in the garage and he gave it a big push and something popped. He said what was that? I said you just fixed your problem. That particular Ford has a spring steel clip on the end of the rod that holds it into the M/CL When he finally applied enough pressure to seat it in place the problem was eliminated. I was shocked to see that there was no way to adjust the length of the rod. We removed the washers and it was in fact just fine. Make sure you have a brake return spring to pull the pedal all the way back up to the stop and take any pressure off of the M/CYL. leaving a slight gap between the rod end and the piston.
GM plunger style brake light switches turn the brake lights on when the plunger is not in contact with the pedal so it wouldn't hold the pedal down and turn the brake lights on at the same time. The vehicle likely has an older Ford brake light switch that turns the brake lights on when there is pressure in the hydraulic system.
This worked out for me too. Most likely the pushrod between the booster and mastercylinder is to long.
x2 My front right caliper locked up like that for a bit till I bled it again and got all the air out.
Ok guys,ur help is priceless....turned out to be the rod between the m/c and booster...1/8" to long! Now they work perfect...thanx..
Also, I had roughly the same thing happen to my Model A...the flex lines going to the calipers was old and the inside of the lines had deteriated....you could use thbrakes a few times and the pressure couldn't release from the caliper.....thus, letting the pads have pressure enough to make the brakes get hot which increased the pressure even more.......Sometimes brakes can make you put your hair out before you get it working right.............Flex line...give them a check it the rod length adjustment doesn't work.
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