I have an '80 corvette and the brake light stays on. Sometimes you can push down the brake pedal about 15 times and the light goes out, but as soon as you are coming to a stop out on the road it comes back on. I replaced the master cylinder, proportioning valve, both front calipers (one was leaking) and bled the whole system. When I bled the brakes I didn't seem to get as much pressure in the back as I did in the front. Can anyone please help?I forgot to include I dont have any rear brakes...

 

Sounds like your rear is leaking, however before checking it all..make sure it's not the handbrake handle/switch that's giving you the problem. If not, check all the lines carefully especially at the junction blocks..they're hard to see in the rear tucked up in the frame.

How did you notice you didn't get as much rpessure in the back as the front???

 

When I was bleeding them there was not as much pressure in back as in front. Eventually I will not have any rear brakes if I dont pump the brakes before every stop. Oh, and Ive checked all the brake lines and they look good....

 

I have a 79 and had the same problem. I had to replace all four calipers and pressure bleed the brakes.

 

if you removed all the calieprs there's air in all the lines, meaning that as you complete the bleeding on more claipers the epdal will get firmer, so if you start at the rear and the front is full of air bubbles then the rears will feel a lot less firm....however if you loose pressure and have to pump it up either one of the calieprs is leaking or the master cylinder itself is internally leaking (if the lines are all fine) If the caliper is leaking you should be able to see fluid on the piston or dust boot, for the MC check the weep slot on the underside.

 

I chased this on my 72 for 2 years. It turned out to be air in the rears exacerbated by the runout on the rear calipers being off. This after 2 sets of calipers and much foul language.

 

OK, here it is---
You have one of two problems, either the brakes have air in them or the rear lines are swelled inside causing a partially stopped up line....I`m betting it`s air.

But you have to bleed these brakes in the following order/pattern. Right rear, then left rear, then right front, then left front.----when you bleed do only three compressions on the brake pedal then bleed, until smooth clear fluid occurs, the pedal compression must be done slowly, instead of fast and slamming.
If you still do not have a strong pedal, replace the rear flexabile brake lines. when they go bad they swell inside choking off the brake fluid.

This will work!!

 

nothing on weep spot underneath

 

I will bleed them once again tonight...let you know what happens...thx art

 

Okay.... I bled the brakes and the same thing is happening. I have no rear brakes. When I slam on the brakes the front locks up. Actually only the left front locks up. To my understanding when you put on the brake the first half is rear brake then the second half is front brake... I have no first half really. Someone please help?!@#

 

This would be my guess...no pressure, no rear brakes...

 

In reply to your private message that you hear a whoose when you step on the brake. A whoose means a seal or the diaphram in the brake booster is leaking. A whoose isn't always bad but can be in indicator if the symptoms are consistent with a bad brake booster. Your symptoms are not consistent with a bad brake booster. Let me recap. You have replaced the master cylinder, the proportioning valve and both front calipers. The brake light on the instrument cluster can come on for two different reasons. One is that the park brake is on and the other is a significant differential in pressure between the front and rear brake "circuits". From your description, I would think it is the latter. So, the hypothesis is there is either a leak in your rear circuit, a bad or sucking seal in the rear circuit or you aren't bleeding the brakes correctly. I assume you are bleeding the brakes properly such that you get a solid pedal before and after you start the car. The pedal will get hard closer to the floor after you start the car. Does it then go soft after you drive? If so, does it happen immediately or does it take a while? Are your rear wheel bearings good? Rotors that are out of spec can cause the problem by allowing the pistons extend too far and suck air. Use a micrometer and see if they are in spec. I think it says how thick they have to be on the rotor. If they don't then give me a shout and I'll look it up. If they are bad, install new ones, bleed the system and see what happens. Bad wheel bearings can cause the problem you are having by making the calipers suck air and not leak fluid. If you do a search on the forum you will find instructions on how to check wheel bearings. If you suspect that a wheel bearing is bad, take it to a service center that is familiar with vintange corvettes and get their opinion - it should be relatively cheap. If a wheel bearing is bad, replace it (or have it replaced - relatively expensive). Then bleed the brakes and see what happens. If the wheel bearings are good, the most likely culprits are the rear calipers or the hoses. I would first recommend replacing the hoses with braided hoses (I got mine from VBP). Get a whole set and put them on front and back. It will give you a significantly more solid pedal in the end. If that doesn't work then replace the rear calipers. I recommend o-ring calipers (ditto there on VBP). If that doesn't work then you will have to think about replacing the steel lines from the master cylinder. We'll talk about that if the former remedies don't work. By the way, you made a statement that "When I was bleeding them there was not as much pressure in back as in front". How did you determine that? Did you actually hook up a pressure gage?