ldyoung

Has anyone experienced this before? This weekend after driving my '79 C3 about two hours on the interstate, I started losing petal and my brake light came on. After inspecting the brake system, I couldn't find any leaks. So I bled the brakes and everything was back to normal until I took on another hour drive then same thing happened again. A mechanic friend says that my fluid might be getting hot. I'm running DOT 3 and all original equipment except the front calipers. Any suggestions? :banghead:


[Modified by ldyoung, 12:38 PM 8/11/2003]

Larry B.

Rotor runout will pump air into the system. The rears are the worst. If you have ever turned the rotors off the car they TEND to do that unsless you indicate to eliminate any run-out.

dath

I agree that you probably have a runout problem. I've heard (and am doing this myself) that you can just shim the runout out of the rotors if it isn't too bad. Basically, the issue at hand is that the factory machined the rotors and spindles as a unit to remove runout, so you may have some runout in the spindle and a "true" rotor would still have runout when installed. Part of the problem is that the Corvette calipers have springs behind the pistons which forces them into constant contact with the pad, so the pistons will be rapidly pulsating if you've got runout, acting like a pump and sucking air back into your brake system.

You may also need new calipers or at least to rebuild the ones you have. I'd recommend getting the stainless steel sleved calipers. I had Napa "rebuilt" calipers that were sucking air back in (I didn't shim the rear rotors as I didn't know about that at the time) and couldn't figure it out. I decided to replace the calipers with sleeved ones and took the old ones apart. I was agast at what I saw. There was quite a lot of visible pitting in the cylinders, so it was no wonder they were able to injest air...


[Modified by dath, 1:48 PM 8/11/2003]

76Frankenstein

Apologies for the hijack, but I am experiencing the same problem. I would think that in order for air to be pumped in, fluid would have to be displaced in a sealed system. There is no evidence of any fluid leak that I (or the local mechanic) can locate. Can the air be getting in without loss of fluid?

bloodvette80

periodically my brake pedal will go down farther than other times. I had a look at my master cylinder with no apparent problems. I have been driving the car like that for months. It may be a squeek or air getting in there, but it seems like it get pushed back out (which i know is impossible). but thats the excuse i will use for now on.

dath

Air can get to places that fluid may not due to molecule size I would guess. You can get air back into the system without displacing fluid. I cannot give much more explanation, but that it can happen. Some containers will hold liquid, but they are not air tight, right? Same concept...

bloodvette80

no i think the theory, or at least the one that I'm gonna make up, is that in the calipers, the seals have a lip. the lip will prevent fluid from leaking out because as you apply the break, this lip is pressed hard against the piston. Air on the other hand coming from atmosphere can more than likely easily pass back passed that lip. Like a circuit setter or one way valve. Of course that would only happen if a negative pressure was generated in some way in your brake system. Might be possible with the rapid pumping motion caused by vibrating brakes. That was jsut a stab in the dark so feel free to take shots at me, becuase everyhting above is totally made up. :boxing