Ajmceachron

PLEASE HELP! I just bought a 79 and it needed a new break job. I installed brand new rotors, front calipers, and pads. I also rebuilt the rear calipers. I went through bleeding them out, kind of a PITA. But anyway, I have great break pressure.

UNTILLLL, I start the car, I loose Break pressure. But also it doesn’t roll. It’s almost like the breaks are engaged. I pulled it out of the garage thinking that maybe the pressure would build, it did not. When I went to back it into the garage, the front left break locked up so the wheel could not move at all.

I would assume that when the car gets turned on, the breaks engage which would be why it doesn’t roll, one break locks, and the pedal looses most pressure. Please help me, I’m not sure how to fix this.

TCracingCA

Brake booster maybe stuck in boost essential, when you start it.

mikep3

Tell us if you replaced or modified;

master cylinder
brake vaccum booster
hoses
how did you bleed the system
What brake fluid

HeadsU.P.

First of all, a Booster is strictly an assist. It does not apply the brakes, nor does it release the brakes. The booster was invented because years ago sissy foots said they had to push too hard on the pedal. Today, the booster assists to the point where a barefoot little girl could use her big toe to lock-up all four tires. BOOST!

The brake pedal height reacts when the engine is started or shutoff because vacuum has been applied or removed from the booster. Again, assist.

A brake system that feels lazy is a booster air leak., not a fluid leak.
A brake system with a pedal to the floor is a fluid leak, not a booster leak.

When you started your engine, you didn't lose brake pressure. Its normal for the pedal to drop.
And the brakes do not engage just by starting the engine.

Your issue of brakes dragging, sounds more like: Pads too thick. Rotors too thick. Caliper not releasing, maybe collapsed rubber hoses.

Ajmceachron

I didn’t replace any of those things. I bled the breaks RR inner, RR outer, LR inner, LR outer, FL, FR. I used prestone break fluid from autozone.

Ajmceachron

The pads and rotors are for this car so I feel that they should not be to big. And the front break is completely locked. The pedal doesn’t quite go to the floor. Therefore I feel that the breaks are all engaging once the engine is on, I just don’t know what could be cause if this.

Rescue Rogers

Your rubber brake lines may be collapsed. Take the front rubber lines off and try and put air through them in both directions....it will also make brakes hard to bleed.

If you have power brakes, a way to check The booster is put your foot on it then start the motor, it should depress as the vacuum builds

mikep3

At the price of a brake hose kit, why wouldn't you just change them out. A plugged hose would allow one caliper to lock up.
https://www.ecklerscorvette.com/corv...1963-1982.html

HeadsU.P.

You could have the correct rotors & pads for your car. But, as noted from a forum post a while back, some rotors / pads are made too thick by the manufacturer.
So, they are doomed right from the get-go and will never wear down correctly. But that's another story.

Another possibility is a ****-eyed pad. Slim chance, but it does happen. The pad gets jambed in the caliper and will lock the rotor.
Also.
The engine doesn't care if the brake system works or not.
The brake system doesn't care if the engine runs or not.
Two different systems that have little to do with each other.
Either the brakes engage and release or they don't. Has NOTHING to do with the engine.

So. In a nut-shell, either the pads / rotors (new I might add) have binding issues, which does happen.
Or, you have one if not two bad rubber brake lines not allowing the brake-fluid to release the caliper.

How do you test the hose? With that tire off the ground, open that bleeder screw. If fluid just dribbles out, the hose is ok. If fluid shoots out like a water cannon the hose is defective. Then the tire will rotate.

Techno

I suggest you take another look at the locked up brake. It might have a visible solution. I don't see how you could have put it together if the pads were too thick, they wouldn't slide in.
These 4 piston calipers are floating piston design- the pistons **** and adjust to the pad. The piston seals allow for this.
Versus the single large piston where the entire caliper floats and thus ***** to adjust.
You also mention the pedal goes to the floor. It shouldn't do this. I think you may have to bleed the brakes again. These may be related. The piston cocked or is bad and thus introduced air into the system.
BTW whatever reason you had to change the calipers could also mean other parts need it. I discovered that brake fluid will absorb water over a long period of time. My open brake line(rear) was ok. My front line(sealed) was rusted and shot. Along with the master cylinder where the cup seals sat.

I totally agree with HEADSU.P. on his assessment for the need of PB.
The only power in my car is the engine and windows.

71chimera

suggest R&R all 4 rubber brake hoses; Rockauto has all 4 in either acdelco or raybestos for under $40 total.

for safety sake alone, they should be replaced every 8 - 10 years anyway.

derekderek

Concur. Don't check the flex hoses. Chuck them.

HeadsU.P.

This procedure is correct except the left front being closest to the master is done last.

Ajmceachron

If I take the caliper off, fluid comes through the lines. So the lines should be fine.

Rescue Rogers

if you step on the pedal and it squeezes the caliper, put doesnt release the pressure after your foots off the pedal, then theres something acting like a one way vavle in your system. You could release the front brake line at the proportioning valve adn see if that release the pressure. If yes then its the valve or the master. If not then theres a blockage down stream acting like a one way.

Ajmceachron

I will give this a try, thank you!

HeadsU.P.

You don't understand. Yes, fluid will come out the line. But will the fluid reverse itself? In other words, will brake-fluid flow both ways in the hose?
That's what we need to know, you need to know. If a rubber hose has internal damage, brake fluid may only flow one direction (applying brakes) but may not release the pads because of a faulty hose. Then you have a wheel lock-up.
To test for that, you open the bleeder screw as mentioned before. If the bleeder drips the hose is fine. If the fluid shoots out under pressure, the hose is bad.

Ajmceachron

I just took another look around, I think that you are right, I need new break lines upfront. I also think that the pedal goes so far down because I need to re-bleed the lines. That is what I am going to do first, because the front lines on the car look original and they need to be replaced anyway. If anyone else has any ideas feel free to share them, thank you so much. I’m glad to see the corvette community is so welcoming and helpful😁

carriljc

Get all four hoses.... and better yet get a braided stainless hose kit and do all four. Make yourself a pressure bleeder if you can fabricate things. Otherwise buy one from Motive. It will make your Corvette life a lot easier.

HeadsU.P.

Now you got it. Those rubber brake lines can fool even the best mechanics. They can appear perfectly fine from the outside, but be defective inside. This allows fluid to travel in only one direction, towards the caliper, but not towards the MC.