dcm1

The brake pedal on my 76 vette goes to the floor and I barely have brakes. The brake light on the speedo comes on too. I replaced all calipers three years ago along with new master cylinder and front rubber hoses. I have no leaks anywhere and I am not losing fluid. The first thing I tried to fix the problem was to bleed the brakes. I flushed the entire system by having someone continually pump the brakes while I held a hose into a bottle and on the fitting. This didn't help. I then replaced the master cylinder, bled the master cylinder, then bled the entire system again. Still no good. I also checked vacuum at the power booster and it is strong. The pedal also goes smooth and easy when it goes to the floor. The parts store says that the new master cylinder could be defective and that if I can't find anything else, they would give me another one to try.

Before I do, does anyone have any ideas?

daniel77350

check your rubber lines...they may be collapsed inside. This means when you press the breaks down fluid goes through, and when you let the brakes up the fluid won't come back up the lines. So the next time you press the peddle, its soft.

Perhaps your rotors are untrue, this would pump air in the system...unless you have stainless sleeved calipers.

If thats not it...then I have no idea. I tried to repair my breaks, but it stumped me and i ended up taking it to a vette shop...He charged an arm and a leg, and all he replaced was the rubber lines, and the booster...which are expencive parts, but his laybor charges where crazy.

Daniel

lbell101

I'm not sure from your post if this is what you did but...
If you continually just had someone pump the pedal without opening and closing the bleeder then that could be the problem.
That method would add air everytime the pedal was released.

The method that works best for me is:
Two persons - one at pedal - one at bleeder.
1. Push and hold pedal.
2. release bleeder and fluid.
3. Tighten bleeder.
4. Release pedal.
5. Push and hold pedal.
and so on until there are no air bubbles coming out.
Start at the farthest bleeder from the MC first.
If you put a piece of clear hose on the bleeder it keeps things cleaner but it's not absolutely needed. Ah- and make sure the MC never gets empty!

68427

Sounds just like the problem with mine. I have literally run gallons of fluid through the system without being able to get a hard pedal. I have changed all of the parts, some more than once. Here is how you can isolate where the problem is. Get some brass flare unions and caps, get two for the calipers and larger ones for the master. Start at the master, cap it and bleed - you can do this single handed. If you can get a hard pedal, the master is okay. Then connect rear lines, then front, beeding system at each step. I traced my problem to the front calipers, which I removed, blocked the pads and rotated and bled to get all the air out - which got more air out, but didn't solve my problem. I then swapped in some supposedly good used calipers which didn't help either. Nor did new brake lines.

So, I gave up and bought some Willwood Superlights, the bracket adaptor is 5" long x 1 1/2" wide 1/4" steel strap bolted in place. Some grinding of the original bracket is required. This will work on stock rotors or you could upsize. The cheapest superlights are about $115 each, or you could use the dynalights which are a little cheaper yet. Look for Keith who posts regularly on this forum, he has a link for some nice looking aluminum dynalight brackets.

The Corvette calipers are heavy cast iron antiques. Good luck

American Boy

To check the master cylinder, when you depress the pedal;

When you pump the pedal, does the pressure build up? And then, the pedal return to the floor. In that case, it's usually the master that is bad.

If you have air in the system, the pedal will go down but if you pump it, the air will get pressurise and then pedal will stay up.

Hope this help

Stephan

R. Bruno

If you haven't already done so, I would take a really close look at the calipers. You can't always see leaks on the outside but you may when you remove them and look at the pads and pistons. The MC could very well be bad, not uncommon for rebuilts in my experience. Rubber hoses also as suggested. The isolation method of blocking each component suggested by someone else sounds like a good idea in MHO. As usual great advice around here. Good luck. let us know wheh you figure it out.

dcm1

I think I'm going to start by replacing the master cylinder again. It's pretty easy but I'll have to bleed the system again. After that I'll probably replace the hoses that go to the calipers.

One other thing. If I take the master cylinder off, and then start the car and press the brakes. How far should the rod from the power booster travel and is it ok to do that with the master cylinder off?

R. Bruno

Not sure why you would want to do that. I'm sure someone will give you a technical answer one way or the other but I would not do it.

BeachinVette

Make sure they are giving you the right master cylinder also. The rod travels about an inch and a half. Remember in the 76 the rod ia adjustable. I have mine adjusted almost all the way out. Don`t buy Auto Zone Master cylinders. I went through 9 once on my wifes Camaro "NO poopie" When they ran out I went to Napa the first one worked.
Hope this helps.
Bob

dcm1

I didn't get the the master cylinder from a chain store. I got it from my local parts store where I've been going for years. We have an Advanced Auto Parts store and a National Auto Parts store locally and I have had problems the couple of times I did get parts from them. I very rarely have problems with my parts store. I have to wait until Thursday until they get more in because I took their last one. I'll let you know how it goes.

If there are any other ideas until then, let me know.