Rear brakes locking up WHY???

['Cuda Hunter]

  The rear brakes on my cuda are locking up everytime I hit the brakes.  I figured for sure it was the combination valve, after I had checked  and bled the entire brake system.  I have installed a diffrent proportioning/meteriing/combination valve from a diffrent car.  The same problem persists even after replacing the valve.  What is my next step.  I figured that I would plumb the front brake system together to get straight hydraulics and diagnose it.  I can't find any parts in my town to put a three way together.   This is driving my crazy.  Or should I say Not Driving me crazy. 

[matt63]

I had a similar problem.  The front brakes were glazed so bad that the back brakes provided all of the stopping power and locked up under even moderate braking.

['Cuda Hunter]

  I figured that was the problem at first.  I changed the brake pads and lightly scuffed the rotor.  The car still had the same problem after that.  I also did the same to the rear brakes along with adjusting the e brake.  thanks

['Cuda Hunter]

  When I am in park and  the car is running,  I hit the gas and my brake pedal goes down around a half inch or so.  When I let off the gas the pedal builds more resistence and comes back up.  I just noticed this when I switched my rear kenstone 14's for a pair of keystone 15's. 

[Bullitt-]

Your brake booster lives on vacuum so higher revs drops the vac, that's not the issue. Different tire diameters will effect braking, have you put much larger tires on the rear than front? Adjustable proportioning valve would be the answer if so.   Earlier when I first read your post made me think of similar problems some friends had back when they used to put air shocks on & jack up the back changing the balance more to the front.

['Cuda Hunter]

  I have had 14's all around the car.  Regular shocks.  I just put the 15's on today and the same problem persisted.  The next step on process of elimination is that the Master cylinder is the problem.  I don't think I have many items left to check or replace.  thanks

[Bullitt-]

BTW congratulations JR MENBER

['Cuda Hunter]

  I forgot to mention.                ROLL TIDE !!!!!!

['Cuda Hunter]

  I have Monday to work on the car and I know that someone has an idea of what's going on.  Anyone?  I guess if I can't figure out my Mopar I will have to work on a Pontiac.   

[Jacksboys]

Are you, by chance, using aftermarket brakes up front?

I had a similiar problem when I changed the front drums to discs(off a 76 dart).  I had to change the master cylinder and got the calipers with the largest pistons I could find.  I am guessing that this solved my problem because I have yet to lock up the rear brakes.

[Hemi Challenger]

Are you useing Dick or shoe if you are useing shoe then recheck your brake again is it the front that lock up or the rear if it the rear then it the way you put them on if they are shoe  that self adjuster was the problem that I was having on mine  GOOD Luck

['Cuda Hunter]

  I have a stock set up for 1973.  I will check the self adjuster and the shoes again.  thanks

['Cuda Hunter]

  I have checked and adjusted the self adjuster and they are working fine.  My shoes aren't in the best shape but the problem is with one rear drivers side tire that locks up as soon as the pedal has any pressure.  I also rebled all fittings and tried to push any junk out of the lines at every connection point.  I found a bubble or two and a bit of junk.  After all this again the rear drivers tire just locks up without giving any of the other brakes a chance to really work.  When I drive it around the block and pull it back in the garage the front disc rotors show just a little bit of warmth so they must be engaging just a little bit anyways but not near enough to equal the rear drivers tire.

[Bullitt-]

Is it possible that the lines out of the proportioning valve were reversed?

['Cuda Hunter]

   No they are correct.