master cylinder not compensating

[willy]

If my master cylinder was not compensating how do you fix that? new master cylinder? what would the brakes feel like? I have a 1968 Charger R/T with 4 wheel power drums and have been fighting a brake problem at low speed. I originally thought I had a vacuum problem but I adjusted my timing and idle speed and now have 17" of vacuum. I bench bled the master cylinder and all 4 wheel cylinders and adjusted the brake shoes so they are just starting to touch. When I back out of the garage I have to stand on the brake pedal to stop the car. Any suggestions?
Thanks,
Willy

[Plumcrazy]

Check to make sure you also have 17" of vacuum at the booster, if you do you have a problem in the power brake booster.

[willy]

I do have 17" of vacuum at the booster and the booster has been rebuilt and is working fine.

[elacruze]

do you have new shoes and fresh drums? If not worn in a little they will feel like crap.

How long have the wheel cylinders been sitting without moving? They can stick.

[willy]

My wheel cylinders, shoes and drums have about 1,000 miles on them. This has been an ongoing problem for a couple of years. Nothing I have tried seems to work. I even took out the power booster and went totally manual and still have the same issue. That's why I asked about the master cylinder not compensating. I don't know what that means or the symptoms if it isn't compensating.
Thanks,

[John_Kunkel]

Not compensating means the rear piston in the MC isn't fully returning when the pedal is released, this keeps the compensating port closed and won't allow fluid to return to the reservoir.

When this happens the front brakes usually lock or drag excessively and the pedal is very hard.

[willy]

Thanks for the explaination. I guess that isn't my problem since the front and rear pistons are all one piece instead of 2 seperate pieces and they are returning all the way. It is almost like I don't have enough travel. I made a plate to bolt onto the brake booster that is .920" thick so i could acurately measure the pushrod distance, so i think i am getting all the travel i am supposed to get. Any other things to look for?
Thanks,

[b5blue]

  I can tell you for a fact if it's working (Booster) and you have no air in the lines, it will be VERY power brake! I had a crappy (New) booster for a year and when I changed it out I darn near knocked my front teeth out on the steering wheel! That booster isn't up to par, 17 lb is plenty of vacuum.
  I had to re-learn how to brake it was so sensitive. I could lock up the brakes with just my big toe! Is it a Midland Ross booster?   

[willy]

Yes it is a midland ross booster. How is the best way to test it?

[Plumcrazy]

How is the best way to test it?

With the engine off put your foot on the brake pedal. When you start the engine the brake pedal should drop slightly.

[maxwellwedge]

Have you got the proper master cylinder - for drum brakes?

Have you bled the brakes with everything hooked up?

[bakerhillpins]

When I back out of the garage I have to stand on the brake pedal to stop the car. Any suggestions?
Thanks,
Willy

How do they work going forward? Same or fine?

[b5blue]

Yes it is a midland ross booster. How is the best way to test it?

I think it's not working (Best I can do online.) because of your complaint. For a year I ascribed my problem to the low vacuum from a 509 cam. I installed a vacuum reserve canister and that gave a second but weak shot of power braking. My symptoms were much as you describe, due to the bell crank assembly from the peddle to the booster, braking is very difficult if the booster isn't right.
  True the adjuster nut on the end of the booster rod that pushes the masters plunger must be just short of the plunger to allow it to fully seat rearward for the next stroke. I used a coffee stirrer stick as a gauge, that is easy to set. I spent a year farting around changing masters, bleeding and re-adjusting that nut before just being fed up and buying a new reman booster.
  Even with 9-11 for vacuum the difference was startling! When this booster (the second one.) failed I converted to manual. I know it failed (Last year.) as it all at once started acting just as you describe...you could barely stop the darn car! Had one of my kids been driving (18-22 yrs.) they would have crashed into something/someone. The first booster worked but weakly, the second worked super until total failure and that was really bad. 

[Chryco Psycho]

the pushrod could also be tto long , did you adjust it when the master was installed

[willy]

I think B-5 Blue is onto my problem. I started the car this morning and didn't feel the pedal do anything. With the vacuum guage hooked up to the second port on booster I had 17" of vacuum at idle. I loosened my master cylinder and heard vacuum escape from behind the master cylinder. Is there another test I could do?
Thanks,

[b5blue]

Mine gave no sign of a problem (both) other than no boost. You may rig some kind of test to draw down a vacuum and see if it retains it for a length of time. (?) 

[willy]

Where can I send mine for rebuild since it is a correct midland ross unit?

[b5blue]

 

[resq302]

booster dewey?

[willy]

I have not heard of booster dewey does he rebuild midland ross boosters?

[willy]

Just to update my post. I sent my booster off for re-build and got it reinstalled last weekend. What a difference I now have brakes at low speed. There must have been a small leak somewhere. Thanks for everyones input in solving this problem for me.
Thanks again
Willy

[resq302]

 

[b5blue]