new front disk brakes lock up.....

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darthdustre

darthdustre

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I have a 1974 duster power brakes , front disk , back drums,new porp valve, new lines, new calipers, new drums and shoe, new master, new power booster......

I started the car for the first time and applied the brakes and the calipers locked up...I used the bleeder to release the pressure but the next time i applied the brakes the same thing happen....


please help
 
Possibly the prop valve is not correct or stuck and not re-centering itself when released? The fluid cannot return to the MC. My guess is it defintely is in the fluid since bleeding allows it to release. Are the rears experiencing the same issue?

Grant
 
Got two suggestions:
  1. You said "I started the car for the first time and applied the brakes and the calipers locked up..." Did you try to drive the car at all? The piston is pushed back into the caliper by the minute wobble of the rotor when driving.
  2. I'm assuming you have the floating caliper system with "ways" that locate the caliper on the spindle. Remove the brake pads and slide the caliper back and forth on the ways. It should slide without hanging up. Check the way for rust or nicks. If it hangs up, use a flat file for metal on the way. I prefer the flat file as it avoids creating peaks and valleys I might create with a grinding wheel.
 
BigBlockMopar said:
Pushrod between brakepedal and MC is too long. Keeps fluid from going back into the MC.
Click to expand...

X2 Figure out if it's really a pressure problem or not and whether it's the master or valve.

So first lock them up, and determine that you can release pressure and calipers at the valve, then try the same thing but release the line at the master
 
2 Darts said:
...........The piston is pushed back into the caliper by the minute wobble of the rotor when driving.....................
Click to expand...


This might be "accidently" functionally true, but it's not by design

The pistons are returned a small amount by the flex of the seal ring. That's why it is so important to have calipers in good shape, IE not all gummed up and with good seals, so the rotors/ pads don't run too hot.

This is a generic drawing, but the idea still applies

calliperseal.jpg
 
The local NAPA sold me a new master cyl and assured me it was for disk brakes. It was a drum master cyl and it did exactly the same thing yours does. I replaced it with the right MC and it worked fine. I went back and they let me talk to their " brake pro" and that dummy swore there was no difference. Check your MC, it could be the same problem I had.
 
Yes, I'd agree with above. It sounds like you got a master cylinder with the residual pressure valve for drum brakes. They are designed to hold pressure in the line and prevent the drums from collapsing the full distance. Disc bakes require no residual pressure.
 
Haven't heard the OP weigh in since starting the thread. Is problem fixed?

Telling whether the MC is for disk brakes or not is easy. The drum brake MC has equal size reservoirs. The disk brake MC reservoirs are not the same size.
 
thanks BIgBlockMopar...you are correct..the booster i have is for a mopar but i believe is for a large car or truck....i need about 1/4" plate or new booster.

thanks everyone for your help
 
darthdustre said:
I have a 1974 duster power brakes , front disk , back drums,new porp valve, new lines, new calipers, new drums and shoe, new master, new power booster......

I started the car for the first time and applied the brakes and the calipers locked up...I used the bleeder to release the pressure but the next time i applied the brakes the same thing happen....


please help
Click to expand...

To unlock brakes, you need to lessen the pressure on the brake pedal until the wheels start spinning again. This is called feathering the brakes.
 
curtmaxwall said:
To unlock brakes, you need to lessen the pressure on the brake pedal until the wheels start spinning again. This is called feathering the brakes.
Click to expand...

He's not talking about "during driving". He's saying he applied the brakes, they locked up, and STAYED locked. This is a mechanical/ hydraulic/ component problem, not operational.
 
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