I have a 68, witha 383. Everything from the firewall and up is brand new. including every piece of the braking system, including all of the lines etc.... My question is, I went for a ride yesterday, and everything was fine. Then all of a sudden, my brake pedal got rock hard and would only go down about .5 inch or less. I had to double foot it to barely slow down. Luckily I was aroud the corner form home and nursed it home. I got home a saw the rear brakes smoking and I got that bad brake smell from the rear brakes. I took the wheels off, and the drums came right off.. I saw no problem in the rear brakes. No craking or anything unusual. I had the wife hit the pedal while I tried to turn the drum and they braked normal, but the pedal still feels like a rock, no movement from the pedal, like it should. I also looked at the front and saw no problem. It feels like a have a crushed brake line or something similiar. But I inspected all lines and found none!!! Any ideas. I thought maybe proportioning valve. but would like feedback before proceeding. Thanks guys

 

It sounds to me as though your brake servo has stopped working!
The best way of testing whether this is the case is to hold your foot on the brake pedal as you start the engine. The pedal SHOULD go down a bit as the vacuum in the intake manifold operates on the servo. If it stays where it is yor servo has gone bad.
All the best.
Graham.

 

Servo?????
You did not say, but do you have power brakes? I have in the past had a booster go bad and did exactly what you are experiencing. Check your vacuum lines to make sure you have a good source of vacuum to the booster also, maybe the line there has collapsed. If the vacuum is at the booster check how much, to operate at maximum the booster needs at least 17 in of vacuum. On engines that have a healthy cam that can sometimes not be attainable especially if the booster vacuum line has a tee in it, like to the PCV.

 

Yes I have power brakes, and I checked the vacuum lines. All ok. The car previously had manual brakes, I changed every single brake component out for brand new. Including all lines, wheel cylinders etc.... I know how manual brakes feel, I could still stop the car when they were still there. The brake pedal barely moves, with next to no braking effort from the brakes. How about a blocked proportioning valve??? I have a new one but don't want to change if I don't have to. Thanks guys....

 

There is a couple of things I would check on the vacuum first. With the car running pull the line off the booster to make sure there is actually vacuum going into the chamber. Next plug the line back in and let vacuum build in the booster. Turn off the engine then pull the line off, you should hear a rush of air letting you know the booster holds vacuum. If not the booster may be bad (leaking) or the check valve is not working properly. I have never run into a plugged prop valve, but it could be possible. Before taking it off I would have someone push the brake pedal and open a bleeder to see if there is flow through the system. Start with the rear brakes, if there is no flow, move closer to the front and try again. By doing this you will be able to localize the blockage. I'm thinking the master cylinder or the booster might be the culprit here. Are you sure you have the lines at the master & prop valve hooked up correctly? (reversed)

 

Yes everything is hooked up right. It has been working perfectly for about a year now with no problems