Dsmith

Ok, I am really getting annoyed. '80 55k miles mint. All new calipers at four corners. Bled the brakes. Good stiff pedal. Drive about 100 miles. Pedal gets mushy. Brake real hard, light comes on. Pump brake pedal, it goes off. Dangerous to drive. Not noticing fluid loss. Will need to get her on stands again and fully examine for leaks. I know all about leaks with the factory calipers. Don't really suspect a leak. How the heck is air getting into the system? I have the factory rotors on. So perhaps they may no longer be true to spec. But does the movement against the pistons cause air to be sucked in through the much improved stainless sleeves that quickly? When I bled the brakes two times ago I did let the rear reservoir fluid level drop way too low, kinda dry. I just added more, bled and then bled weeks later. Now this? You know I have a '87 Cavalier Z-24 w/160k+ miles and never had to worry about it's brake performance. #@%& me off! :confused: :mad

Jenny

I have the same problem. My bleeders were not holding brake fluid in. They leaked very slowly, but when fluid goes out, air goes in... and that != good. This is happening to me with Stainless calipers aswell... make sure to check all four bleeder screws on the back calipers. you can usually tell if there's fluid leaking by feeling for moisture or looking for channels where fluid dripped down the side of the caliper. Hope this helps!! And yes, it is VERY VERY annoying. :mad

427V8

Check your rotor runout. It should be .002 to .005 inches. No more no less!

If the runout gets too high it will pump air into your brake fluid causing said spongy pedal :(

Barry's70LT1

Dsmith,
As Keith said, rotor runout is the main cause of the problem you described.
A little detail, you may already know this stuff.
On "regular" cars, when a rotor has runout (warped), you sometimes can
feel the brake pedal pulsing when you are stopping.
Corvette brakes cannot tolerate any runout/warped rotors, even if you don't
feel it in the pedal. The brake pistons follows the warped rotor and acts as an
air pump, pumping air into the brake system/lines.

As Keith said, all four rotors need to have less than .005 runout.
You need a dial guage to check it properly.
New rotors or "turning" the rotors is not necessarily a fix, as the spindles or
hubs may be the cause, and the rotors are actually "true".

If your rotors look to be in good shape you can always "shim" them back
to an acceptable tolerance.
If you need help with shimming information, just ask. Lots of folks here
have "been there, done that".

Barry

Dave68

FYI: o-ring sealed caliper pistons are more resistant (ie-can tolerate more runout) to air inclusion due to rotor runout. However, since you already have good calipers, shimming may be necessary.

68427

I am fed up with Corvette calipers and am installing Willwood billet superlights on front, I should have is completed and installed by the end of the month. This is an easy conversion, you can use stock rotors and a simple bracket made from 1 1/2" wide 1/4" thick steel stock. Some grinding of the stock bracket is required. An added bonus, save about 10lbs per wheel.

jerryp58

I sympathize with you. I think the big reason I got rid of a '68 Mustang years ago was because I was so disappointed in the brakes after all of the work I did on them.

You say you let the fluid in the master cylinder get low. Did you bled the master cylinder after that?

Dsmith

No I didn't bleed the master cylinder after I left one bank get too low. I will post a question on how to bleed the master cylinder.

427V8

These are the exact reasons I am also changing over to Wilwood calipers, except I'm using Dynalites instead since they are quite a bit cheaper :)

Of course I did it the hard way with all new brackets :rolleyes: