Brake Pedal Low
Thread Starter
Heel & Toe
Joined: Mar 2006
Posts: 24
Likes: 0
Brake Pedal Low
Hi, I have a 73 vette and recently took it to the garage because the brake pedal was low. It needed new rotors, calipers, master cylinder and a booster. After the work was done, I picked up the car and within a few hours I had no brakes again. I have subsequently taken it back three times and they checked everywhere for leaks (they said they found a very, very small leak at the proportional valve which they fixed). The last time they bled the brakes, they used a Power Bleeder because they thought maybe conventional bleeding was not working right. I picked it up again the other day and drove 2 hours on highway. When I exited, no brakes. The car has headers and the Proportional valve and lines are fairly close. When I opened the hood, I saw some brake fluid towards the driver end of the master cylinder (leaked from cap?). This is the first time I have seen that. The Master cylinder was hot. Could it be that the fluid is boiling and putting bubbles in the lines (brakes get no better when the car is cold).
I am really perplexed about this one and would appreciate some expert advice ....Thanks!
I am really perplexed about this one and would appreciate some expert advice ....Thanks!
Team Owner
Joined: Aug 2006
Posts: 24,125
Likes: 15
From: Columbia Missouri
One thing I can think of, is rotor wobble, also called runout, is causing the caliper pistons to suck air into the system. If the new rotors were installed and the runout was not checked and fixed then you might have pumped a lot of air into the brake system. That might explain why fluid was puked out of the master.
If the runout is not checked and fixed you'll never get all the air out of the system.
If the runout is not checked and fixed you'll never get all the air out of the system.
Le Mans Master
Joined: Dec 2007
Posts: 6,422
Likes: 591
From: McHenry Illinois
You might try some header wrap or insulation to keep the lines and valve cool and try it again. Did the shop say where they found the air, front or rear?
Another thing that can happen on C3's is that if there is too much rotor run-out, the caliper seal can let air into the fluid while driving. Do you know if they checked for rotor run-out ?
Another thing that can happen on C3's is that if there is too much rotor run-out, the caliper seal can let air into the fluid while driving. Do you know if they checked for rotor run-out ?
Last edited by '75; Oct 21, 2008 at 06:11 PM.
Thread Starter
Heel & Toe
Joined: Mar 2006
Posts: 24
Likes: 0
Thanks, I have seen this mentioned in others posts as well. So air can be sucked into the system at the calipers without any evidence of a leak ? I will have the shop check the runout. I think I read somewhere it should be under 0.003 inches ?
Do you think the heat idea is possible or likely not?
Do you think the heat idea is possible or likely not?
Thread Starter
Heel & Toe
Joined: Mar 2006
Posts: 24
Likes: 0
Thanks for that idea as well !
I will wrap the headers and protect the lines as well as take it in to have the rotor run-out checked. Now that I am thinking about it, nothing has really changed with the headers (I have always had them) so maybe they did not get the run-out correct.
I will wrap the headers and protect the lines as well as take it in to have the rotor run-out checked. Now that I am thinking about it, nothing has really changed with the headers (I have always had them) so maybe they did not get the run-out correct.
