Rear Drum Brake Lock Up: How Have You Fixed This?

[Road_Runner]

Had another opportunity to panic stop in the Barracuda today when the minivan right in front of me on the highway decided they didn't want to be in the exit-only lane so she came to a complete stop on the highway waiting for an opportuniy to change lanes!  So I stabbed the brake pedal pretty hard and the rear brakes locked immediately sliding the tires while the fronts were a good ways from locking and I really wanted to stop faster but didn't want to swap ends so I let off a little.  The Roadrunner has 11" drums all the way around and never was this easy to slide the back tires.  The Barrracuda is a 73 with std front discs and the smaller 10" rear drums which probably have something to do with it, but the car isn't really safe as is so I'm asking what others here have done to resolve this.  I know aftermarket rear discs are an option, but I have to believe there are changes to make these drums work better than mine are working now.

Thanks in advance, Jim

[wiging19]

Just have to ask don't you have a portioning valve you could adjust to get them where you want?  If not I'd just replace what you have with one that has an adjuster.  Then adjust them under a few panic stops in a parking lot until they are the way you want.  Many cars today still use drum brakes on the back and stop fine.  The key is finding the balance on yours where the rear doesn't lock up.  I had drum brakes all the way around on my 70 challenger.  I converted to disc on front.  It was significantly better but I wanted more.  So I converted to police size rotors using Chrysler parts outlined in this forum.  Now that I'm putting 750 horse power engine in I'm putting disc brakes on the rear because the momentum I'm able to call on is significantly above the norm for my cars original design.  After all the money and love I've put into the car I don't want to lose it if I have a stupid moment with the throttle.

It has been ten years since I bought all new brake parts for my car but I replaced everything (springs, pads, etc.).  The end result was as the brakes were as good as the Honda which basically had the same setup.  Just my opinion.  I'm sure others have opinions.

[brads70]

When I first got my car and was replacing all the brakes. I read on here about using truck wheel cylinders on the rear to prevent rear wheel lock up. At the same time as I installed them I also installed a wildwood brake adjuster. I never needed it and it still sits wide open. This was with discs up front and drums out back.
Thought this might be an option for you? Cheap to try?

[Road_Runner]

Just have to ask don't you have a portioning valve you could adjust to get them where you want?  If not I'd just replace what you have with one that has an adjuster.  Then adjust them under a few panic stops in a parking lot until they are the way you want.  Many cars today still use drum brakes on the back and stop fine.  The key is finding the balance on yours where the rear doesn't lock up.  I had drum brakes all the way around on my 70 challenger.  I converted to disc on front.  It was significantly better but I wanted more.  So I converted to police size rotors using Chrysler parts outlined in this forum.  Now that I'm putting 750 horse power engine in I'm putting disc brakes on the rear because the momentum I'm able to call on is significantly above the norm for my cars original design.  After all the money and love I've put into the car I don't want to lose it if I have a stupid moment with the throttle.

It has been ten years since I bought all new brake parts for my car but I replaced everything (springs, pads, etc.).  The end result was as the brakes were as good as the Honda which basically had the same setup.  Just my opinion.  I'm sure others have opinions.

I do need to check the adjuster assuming it has one.  Funny thing is that the only thing I've changed is put bigger tires front & back and the original lady owner I assume drove this car for 130k miles with it set the way it is now.  I may go to 400+ HP with a small block and will put rear disks if I have to, just want to make the disc/drum setup work if I can.

Thanks, Jim

[Road_Runner]

When I first got my car and was replacing all the brakes. I read on here about using truck wheel cylinders on the rear to prevent rear wheel lock up. At the same time as I installed them I also installed a wildwood brake adjuster. I never needed it and it still sits wide open. This was with discs up front and drums out back.
Thought this might be an option for you? Cheap to try?

That could work, do you know what year/model Dodge truck wheel cylinders to ask for, 1973 like the car?

Thanks, Jim

[mopar jack]

Rear wheel cylinders for 1978 and up dodge light trucks and vans are 7/8 inch. Napa p/n 17507 left and p/n 17508 right.

Jack

[HP_Cuda]

Proportioning valve will definitely help you here.

As stated, have a nice wide open area and give her gas, get to speed and stab the breaks. Keep adjusting till the fronts lock up just hair before the rears.

[Road_Runner]

Rear wheel cylinders for 1978 and up dodge light trucks and vans are 7/8 inch. Napa p/n 17507 left and p/n 17508 right.

Jack

Awesome, thanks for the info!

Jim

[Road_Runner]

Proportioning valve will definitely help you here.

As stated, have a nice wide open area and give her gas, get to speed and stab the breaks. Keep adjusting till the fronts lock up just hair before the rears.

I'll definitely try this first.  Plus, I'm going to pull the back wheels and see if anything looks like it needs attention.

Thanks, Jim

[dodj]

I'll definitely try this first.  Plus, I'm going to pull the back wheels and see if anything looks like it needs attention.

Thanks, Jim

The adjuster works well for me. I was surprised how much I had to 'choke off' the rear brakes. Quite a bit.

[Road_Runner]

The adjuster works well for me. I was surprised how much I had to 'choke off' the rear brakes. Quite a bit.

Agreed, my backs lock up way before my fronts are even hauling down the car.  My wife said I'm used to antock brakes and thats probably true, but the Barracuda is flat out unsafe as is. 

Later, Jim

[mopar jack]

Had this same issue on my 71 Road runner all drum brakes after the master cylinder started leaking. Replaced the cylinder but the rear brakes would lock under normal use. Turns out that the safety proportioning valve moved to block off the front brakes and stayed in that position only allowing pressure to the rear brakes. Couldn't repair so I just replaced it and that solved the problem.

Jack

[burdar]

The very first thing to do is make sure the rear brakes are dry.  If a wheel cylinder is seeping, or a rear axle seal is bad, it will cause what you are describing.  Even moisture from a lot of humidity can cause it.  If there is a large buildup of brake dust inside the drums, it doesn't take a lot of moisture to cause problems.

[LRT545]

Consider the age of your rear tires?  Old tires turn into 'hockey pucks'.   They may look good, but will go hard after 4-5 years which will affect traction.

[rattlesnake]

If the rear tires have decent rubber your problem is in the proportioning valve. The front brakes are activated by pressure created by the back brakes. The proportioning valve will not open to the front brakes until a certain amount of pressure is built up. I would say it is not working properly or your tires are junk. Now where the back adjusters come into play is setting the pedal height.