Sloppy Brakes

[73'cuda]

I hope I am doing this "posting" correct. Hi everybody, who reads this . . . My name is Jim and i bought a 1973 'cuda this last Decemebr and man, was it a mess.
I have replaced everybit of the rear drums and all brand new parts for the front discs. I've rebuilt all of the braking system and today just repalced the master cyclinder.
My brother and I can get the brake pedal really hard without the car running. It has power brakes. I have not replaced the power booster.

As soon as the car is running, the brake pedal gets real sloppy and will go more than 1/2 down to the floor. The minute, you turn it off, the pedal goes back to being rock hard.
ANY IDEAS?

 

[Chryco Psycho]

Welcome Jim
Did you adjust the length of the brake pushrod out of the booster , when you swap master that will usually need adjusting . It may need to be lengthened
Other then that try driving it , you very rarely push the brake to the point where the pedal is hard , you may have good feel with mild [typical] brake application

 

[Big Jim]

You may just need to adjust the rear brakes, loose shoes eat a lot of pedal travel to engage. Old school way of being sure all air is bled out is to step on pedal and drop car in gear- when trans takes hold if pedal moves down, there's still air in the system.

 

[ramenth]

The brake pedal is going to be rock hard with the engine not running on a power assist car. No vacuum, no boost. Crank the engine, get vacuum, get boost.

A few other questions for you. Is this the first time you've used the brakes since you rebuilt the system? Remember, after doing a brake job, especially on front disk, you need to pump the pedal several times to get the pads moved.

Did you bench bleed the master?

Did you re-bleed the entire system after you replaced the master? Sometimes not necessary, but I do it any way as cheap insurance.

 

[73'cuda]

we bench bled the master cycleinder and then bled each wheel from the closest wheel to the farthest wheel. As we did each wheel the pedal got firmer and tighter as we bled. Did all 4 and the pedal went from the floor to like an inch down and firmness.
We thought we were good. We then started the car and the pedal traveled 1/2 way to the floor. Turn the car back off and the pedal is real tight again.
We did not do anything with the "proportioning valve" i think it is called.
Does anybody know anything about that? Could that vavle do this?
I will adjust the shoes in the back, once more and check the brake rod length.
THX

 

[Chryco Psycho]

generally it is better to bleed the furthest wheel first & work back to the closest for future reference , I doubt it is affecting the way it is now

 

[burdar]

Re-bleed the system starting with the farthest wheel from the master. End with the closest wheel from the master. After that, adjust the rear shoes so that there is just a slight amount of drag when spinning the wheel. The rear shoes are adjusted by turning the star wheel at the bottom of the backing plate. There are access holes in the backing plate so you can make adjustments. MAKE SURE TO USE JACK STANDS WHEN YOU ARE ADJUSTING THE REAR BRAKES. DON'T GET UNDER THE CAR WITH JUST A JACK FOR SUPPORT!

If the pedal still hasn't improved, pull the master off and check the pushrod length. You should have about a 1/16" clearance from the end of the pushrod to the inner master piston.

 

[73'cuda]

THank You all, i will try adjusting the rear brakes. That sounds like the only thing left, beside pulling the master cyclinder back off.
THANKS ALL