Intermittent and Tempory Brake failure Issue
Thread Starter
4th Gear
Joined: Sep 2012
Posts: 4
Likes: 0
Intermittent and Tempory Brake failure Issue
The car a 72 without power brakes. The brakes seem fine. I have no leakes, flushed new fluid 5 qts through the all bleeders to make sure I have good clean fluid. Start driving and the brakes seem fine. After I drive 15 or 20 minutes the pedal goes way down and the brake dash light comes on. When it sits a while they are fine again. They are not over heating or being used hard. But it does seem when they get to operating temp it happens and whan they cool it goes away. Any ideas?
Supporting Vendor
Joined: Mar 2008
Posts: 576
Likes: 3
From: Muskegon MI
Sounds like a classic rotor run out issue. Check your rotor wobble. Another possible issue is that a brake line has been run to close to the exhaust and you are boiling the break fluid. Those are the two that immediately come to mind.
Andrew
800-442-0335
http://www.muskegonbrake.com
Andrew
800-442-0335
http://www.muskegonbrake.com
Team Owner
Joined: Sep 2006
Posts: 31,287
Likes: 4,375
From: Westminster Maryland
Hi PRH,
Welcome!!!!
A 72, VERY NICE!!!!
How about a few pictures of your car for us to enjoy?
Since you start with firm brakes before you drive is it possible that the rotor (s) on a wheel (s) are pumping the the caliper pistons and pulling air into your brake system?
Have you checked the rotors for 'run-out? It's especially important on the rear brakes.
Regards,
Alan
Welcome!!!!
A 72, VERY NICE!!!!
How about a few pictures of your car for us to enjoy?
Since you start with firm brakes before you drive is it possible that the rotor (s) on a wheel (s) are pumping the the caliper pistons and pulling air into your brake system?
Have you checked the rotors for 'run-out? It's especially important on the rear brakes.
Regards,
Alan
Racer
Joined: Sep 2007
Posts: 288
Likes: 1
Melting Slicks
Joined: Mar 2007
Posts: 2,520
Likes: 11
From: Hinckley OH
I thought of boiling brake fluid when I read that they come back after sitting.
Thread Starter
4th Gear
Joined: Sep 2012
Posts: 4
Likes: 0
Thanks for tips. A while is an hour or so. I park it and when I go back it is fine. I never timed it. It did it before the fluid flush. That is why I flushed the fluid thinking that might help. The brake lines have not been moved so thats not the issue. I will check the disk wobble. However I would think I would feel that in the brakes. Wouldn't I?
Do you think it is possible that the fluid in the bottom of the calipers is bad and boiling at temp. The bleeders are on the top so the bad fluid could be staying on the bottom. Any thoughts?
Do you think it is possible that the fluid in the bottom of the calipers is bad and boiling at temp. The bleeders are on the top so the bad fluid could be staying on the bottom. Any thoughts?
Race Director
Joined: Jul 2001
Posts: 15,892
Likes: 42
The brake light coming on indicates that there is a flow/pressure imbalance between the front and rear systems. The only way this can happen is if there is an external fluid leak, air in the caliper, or a faulty master cylinder.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Thread Starter
4th Gear
Joined: Sep 2012
Posts: 4
Likes: 0
Update
I checked the disks and they run true so that is not it. I parked the car and let it idle for a long time to see if it was heat from anywhere else. The brakes were still fine sitting in sitting in the driveway. Good pressure and no lights. So heat from other sources is not the issue. It has no leakes. I drive it a short distance, and the pedal all of a sudden starts going almost to the floor and the brake light comes on. But let it sit and it is fine again. I am stumped.
Advanced
Joined: Jul 2007
Posts: 72
Likes: 2
I too suspect it is the master cylinder. If you think your master cylinder is the original then it has had 40 years exposure to the development of rust pits on the sealing surface and deterioration of the internal seals. A new master cylinder that exactly matches the one that came on the car can be purchased for about $125.00. If nothing else shows up in troubleshooting then master cylinder replacement is strongly suggested. I would not drive the car the way it is.
Le Mans Master
Joined: Jan 2000
Posts: 8,918
Likes: 27
From: New Hill NC
If it in fact comes back without bleeding, it has to be something that either boils the fluid or pushes the pads back enough to cause a low pedal. My guess is a collapsed rubber line, or as mentioned a badly adjusted master cylinder. Either would heat the fluid up. Another remotely possible cause would be a sticking hand brake shoe.