Brake pedal wont come up

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hardcharger426

hardcharger426

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Hey Mopar guys,

I need help. I have a 71 duster with the 73 disc brake conversion on it.
Problem is my pedal will not come up. If I pump the brakes by hand it locks up the front brakes. If I open the bleeders, brake fluid comes out and they release.

I ran it on stands and the back brakes seem ok.

I have new brake lines, hoses, 73 disc brake master cylinder (second one), and caliper pads and rotors also stock prop valve.

I bench bled the master and bled the brakes all the way around about 5 times, I also put a block of wood under the pedal so it wouldn't over extend.

My only guess would be that the fluid isn't returning to the reservoir.

The car has a booster on it and the car was a manual brake car originally.

Are the master cylinder brake rods different lengths?

I also assume that there is not a return spring for the brake pedal and the master cylinder spring pushes the pedal back out.

Any help or ideas would be appreciated

Thanks guys.
 
The piston is likely not returning past the compensating port, and likely due to the pushrod length.

To find out, pump up the brakes and lock them up, then crack the nut right at the master. If you have pressure there, it's the master
 
already did that. The brakes were still locked up.

Anybody know the correct length of the pushrod for 73 disc brakes with a booster on it????
 
Is this a completely new swap,or no? What have you recently changed? Let's start there.
 
When you changed it over did you use every part of the doner car?

I agree that it is a release issue on the master cylinder.

Years ago (you are jogging the cobwebs in my head) I bought a stock replacement master cylinder for a 78 CJ-7 I had at NAPA.
For some reason I had the same problem you are describing.
Turned out the master cylinder looked identical but where the rod mated up with the plunger, there was two different distances on the plunger depth depending on the year.
They gave me the wrong year master cylinder, or it was boxed wrong.
 
I bought a non running project car that already had the conversion on it. I doubt it had been driven with it. It was on its way to becoming a drag car.

I kept the spindles and a arms and replaced everything else with new parts for a 73 except the booster, prop valve and rod.

I did try the master that was on it before, same thing.

Bleeding was done with a vacuum RR,LR,FR,FL.

I don't know what the rod came from, it was in the booster when I got it.
 
make sure where the bolt and nut that goes thru the brake pedal and push rod is not over tighten..
 
67Dart273 said:
The piston is likely not returning past the compensating port, and likely due to the pushrod length.

To find out, pump up the brakes and lock them up, then crack the nut right at the master. If you have pressure there, it's the master
Click to expand...


Dart. I did the above. When I cracked the nut the brakes were still locked up
 
Is there any chance the proportioning valve is plumbed backward?
 
I've loaded some pics of the master and the rod
Can anybody verify that this is the right rod length????
Also have a pic of how the prop valve is plumbed, Anybody think this is wrong?
 

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I had a similar thing happen when a small amount of crud got into the return hole at the bottom of the master cylinder. Other than that the pistons could be in wrong ?
 
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