Technical Drum Brake Problems

I need help. I have a 1955 Plymouth Plaza with factory drum brakes all the way around. They have always work fine but a couple of years ago I upgraded to a dual pot master cylinder for safety. I also either rebuilt or replaced all my wheel cylinders at that time. Everything worked fine until this past fall. My car had sat a while and when I went to drive it the master cylinder was dry. One of my front right wheel cylinders and my right rear wheel cylinder were leaking. I finally got the car up on a friend’s lift and rebuilt both wheel cylinders. Now for the problem. When I go to bleed the brakes, I am sucking air. I can bleed the front but when I move to the back, the peddle goes to the floor and lots of air. The reservoir still has fluid in it. Any ideas on what is happening?

 

Did you start bleeding at the right rear?

 

Start bleeding at the rear, farthest from the master cylinder. do both rear, the front farthest from the master, then the other front. Even if you only rebuilt 2 wheel cylinders, you will need to bleed them all. Any other way will not remove the air. Gene

 

If you are sucking air at the wheel cylinder you didn't happen to reverse a cup in one of the cylinders? I've fixed a couple sets of "we changed the brakes on Saturday" brake jobs where someone reversed the cup because they couldn't get it to go in the way it should.

I've also seen a few guys who tried to bleed the brakes with the drums off and that doesn't work well at all.

 

Try a wrap of Teflon tape on the Bleeder Screw threads, that's been know to help at times.

 

Have you bled the master also, being you say it went dry?

 

Definitely go with bleeding the master first in this case. A good power bleeder may work well too. Unhook the lines at the master and bleed it, will probably require a helper.

 

I made a mistake in my post. I can bleed the back but when I move to the front, the peddle goes to the floor and lots of air.
I bled the MC and can get 2-3 good bleeds and then lots of air. The MC never gets low during this.
The old setup was a single pot MC that had one line that split at the fender well and went front and back. The new MC has two lines. I didn't change anything else and this setup has been working fine until recently.

 

you have another leak somewhere

 

Your master may be toast. If you push it past the limits of normal use, the bottom of the bore is where moisture and other crud collect, even rust. Push a rubber cup past that line and it can be damaged.

 

I'm with Bob.
Master cylinder may be bad

 

I'm with Bob also as the master when it went dry saw air first and possibly rusted the bore and is ripping the cup . `

 

Sounds like Bob is correct. Don't forget to ADJUST the shoes PRIOR to bleeding the wheel cylinders.

 

I will change out the master cylinder and report back.
Also, do you think since I went from a single pot MC to a dual pot MC that I need to install a proportioning valve?