Help! 1978 brake problem

[gaC5]

On my 78 I've had it in 2 garages trying to fix my brakes but neither one has fixed my problem. Just driving in town braking works fine. If I drive it on the highway any. Even for just 10 miles when I go to brake the pedal goes down almost to the floorboard and the brake light comes on and stays on. I've taken it to my mechanic twice and he says he has checked everything on the brakes and that the only thing he can find is that there is air getting into the lines. So he bleeds the air out of the lines and they are ok until I drive it on the road again. After paying twice for doing this work and it didn't fix the problem I decided to take it somewhere else. I took it to Best Buy and the mechanic there said the other mechanic might not have checked the rear brake lines. So he says he will check everything out. When he gets back with me he said he looked at everything about the brakes and that the only thing he could find was the air in the brake lines. He or the other mechanic didn't know air was getting in them and said there was nothing else he could do. Would aprecciate it if anybody would know anything about how to fix this problem:eyerole

 

[bill81vette]

you took this vette to Best Buy to get fixed??????

how old are the brakes on your vette,are they original,been replaced????
does you steering wheel wiggle back and forth when you step on the brakes????

 

[Vettehead Mikey]

My guess is that one or more of the brake rotors has been removed and turned or possibly replaced with a new rotor. Although common practice on modern cars, doing this on C2 or C3 Corvette runs the risk of creating lateral runout on the rotor surface. If not corrected, the side-to-side movement of the rotor will 'knock' the pistons back into the caliper and draw in air past the seals. The air gives the soft pedal and bleeding it out restores braking action- till you drive the car again.

Take the wheels off to see if the retaining rivets holding the caliper on the hub or spindle are still there.

 

[gaC5]

you took this vette to Best Buy to get fixed??????

how old are the brakes on your vette,are they original,been replaced????
does you steering wheel wiggle back and forth when you step on the brakes????

bill81vette I meant Best One:L

 

[gaC5]

My guess is that one or more of the brake rotors has been removed and turned or possibly replaced with a new rotor. Although common practice on modern cars, doing this on C2 or C3 Corvette runs the risk of creating lateral runout on the rotor surface. If not corrected, the side-to-side movement of the rotor will 'knock' the pistons back into the caliper and draw in air past the seals. The air gives the soft pedal and bleeding it out restores braking action- till you drive the car again.

Take the wheels off to see if the retaining rivets holding the caliper on the hub or spindle are still there.

The brake rotors haven't been removed or turned for a long time. But it won't hurt to take the wheels off and check the retaining rivets. Thanks

 

[SVO]

The brake rotors is/was riveted to the front hub or the rear spindle. The brake caliper is bolted to the caliper support. But what you are experiencing is classic excessive rotor run-out. The factory shop manual has the procedure and the spec's for checking the run-out.