Rear brakes locking up WHY???

[jeryst]

I had a similar problem with a car that I bought long ago. After a lot of  messing around, I found that the previous owner had replaced the vacuum booster  on the master cylinder with one that was not correct, even though it looked the same. Once I changed it, everything worked fine.

['Cuda Hunter]

  And you had only one tire in the rear locking up because of the vacuum booster.  Interesting, I will look at that.

[matt63]

Just to elaborate on my original theory, you could back the rear brakes off totally or somehow temporarily disable them to see how effective the front brakes really are.

['Cuda Hunter]

  I did block off the rear brakes and the front didn't work as well as I had expected so I replaced the proportioning valve.  The same problem persists. 

[heminut]

If you are only locking up one rear wheel that is usually caused by improperly adjusted shoes (one shoe adjusted out more than the other) or the shoes on one wheel being contaminated with oil or brake fluid. I would suggest putting a new set of shoes on the back and having the drums turned.

[Chryco Psycho]

are the shoes new ? are they contaminated with oil or are they hardened or cracking ? the shoes may need to be replaced

['Cuda Hunter]

  I am going to replace the shoes and maybe the drums.  The one wheel would still lock up after I had totally unadjusted the self adjusters.  The pads aren't the best looking nor are the drums.  Drums mostly look crappy because of a lot of rust has eaten away some of the exterior, however the inside of the drum still looks reasonable.  There is no hardening or cracking or contamination.  There is a slight amount of glaze on the pads.  I will change the shoe pads next and see if that really makes a diffrence.  I have been trying to fix this without just throwing money at parts that could be replaced.  I seem to throw a lot of money at stuff to get it fixed. 

[Bullitt-]

For what it's worth, the 73 manual references that lock up on drum brakes can be caused by stuck piston in the brake cylinder. I suppose that means the piston can't retract keeping it in the on position therfore when you apply pressure there is little travel before contact.

[wiging19]

If you are only locking up one rear wheel that is usually caused by improperly adjusted shoes (one shoe adjusted out more than the other) or the shoes on one wheel being contaminated with oil or brake fluid. I would suggest putting a new set of shoes on the back and having the drums turned.

  I had the same problem with my car.  Nearly drove me insane.  I replaced practically every part of the braking system before I realized that the spring to one adjuster was slipping lose when I braked.  Causing uneven braking and causing the car under hard braking to dance all over the road.   My solution was to bend the spring a little more so that both adjusters worked correctly.   Check this out.   Took me three years to figure that one out and it cost me close to 3 grand in parts.

 

[Mt.St.BigBlock]

Try disconnecting the E-brake cable inside the drum on that side. It could
be hung-up by rust and hasn't returned to its "home" position. Jeff

[Challenger6pak]

You could have a partially blocked line that is not allowing the wheel cylinder to retract all the way.  When you hit the brakes it is closer to engaging than the other side causing it to lock first. 

['Cuda Hunter]

  Sorry guys,  I am very busy running a business during the days and don't get many chances to talk during the day nor do I have a chance to work on the Cuda much at nights.  Once or twice a week at night and one day on the weekend is all that I can afford.  I will be checking into each one this weekend.  This is driving me nuts.
  Lots of these thoughts and experiences are pretty good and I have given many consideration so far.  Everything helps.  One of these suggestions is bound to work.  THANKS

['Cuda Hunter]

  I figured out that the brake booster is not working.  First I properly adjusted the brake booster push rod then the booster still would not provide any assist.  Next I pulled the metering valve stem to overide the metering valve.  I gave it a good brake stand and drove it for a little while and got the vehicle warmed up.  I was still getting lock up in the rear but at least with the front manually operated I could get a little of front brake.   After driving around the neighborhood for a little while I pulled back in the garage and pulled the rear tires and drums.  Since I got the rear axle warm for the first time I noticed that the brake pads looked glazed again.  I touched them and it felt like glue.  Upon this I realized that the rear axle seals were leaking on the brake system hence causing the rear brake to lock up.   Now I just need wheel bearings seals and a brake booster.  I had a good friend who happens to be ASE certified who helped and pointed out simple things that me as the amateur did not see. thanks to everyone who gave their thoughts.  I will post again next weekend when I have everything put back together and it works, hopefully and probably. 

[Chryco Psycho]

locking brakes is generally caused by oil on the shoes / pads

[Jacksboys]

Good luck on the fix.