Please help with brake issues

[JayBee]

Here's what I have:
10 inch drums, non-power assist. Lots of lining on the shoes. NO leaky wheel cylinders. Master cylinder is full and no loss of brake fluid.

Here's what's happening:
If I have to stop suddenly, the pedal goes real low and the brake light comes on, BUT if I give the pedal even just one pump it doesn't go low and the car stops decently. Also, once stopped, the pedal stays there. It doesn't creep down while I'm sitting there and giving it pressure.

What could be wrong? I've adjusted the front brakes so that there's just a bit of resistance to free wheeling when I spin the tires. Should I adjust them further? More questions. Can the rear brakes be adjusted the same way as the fronts? How do you tell if there's some spinning resistance what with gears and the Sure Grip holdin it back?

Thanks for any replies. Oh, before it's suggested, a disk brake conversion is not happening any time soon. 

[MEK-Dangerfield]

John,

  Back in the day I had a 74 Dart that acted the same way. I would give it a quick pump, then I would be fine stopping. The pedal was hard after that initial pump. I thought it was the brake system not being bled properly, but back then I wasn't capable of such a task, so I lived with it. Have you checked if there is air in the lines?

[JayBee]

Thanks Mike. They say there's no dumb questions, but these sure sounds dumb. How do I check for air in the lines? Is re-bleeding the way to find out? I'm still curious about adjusting rear brakes too.

[MEK-Dangerfield]

Yeah John,

  I was thinking about re-bleeding.

[72rtchallenger]

sounds like it needs rebleeding for sure

[CHL2T]

The (manual) brake pedal in my Challenger was the exact same way, quick pump and rock hard after. After the disc swap and tons of bleeding.......same thing

[tman]

How old is master cylinder?  Sounds like the beginning of the master cylinder failing, internal leak between seals.  You can rebuild it or just get a new one. 

[72cudamaan]

Usually you can feel the resistance on the brake drum.  Other possibility is to over adjust the rear shoes, then back off the adjuster a coupla clicks.

[BIGSHCLUNK]

John, have you done any thing like new lines/wheel cyls??? My buddy had a wierd prob on his RT/SE and it was  due to unmatched parts. Degree angle wise that is....  Other than that bleedem' my friend! 

[Chryco Psycho]

it could be it needs to be adjusted again , often if a second pump bring the pedal up the adjustment is off

[mopar12372]

  if it still goes to the floor and you dont have a fluid leak replace the master cylinder

[JayBee]

John, have you done any thing like new lines/wheel cyls?

New wheel cylinders installed last spring and after that the brakes were great. No need to pump and high pedal.

Maybe I should have mentioned that this all started happening last September when I had to come to an emergency immediate stop from 50mph because someone 2 cars ahead of me didn't know how to merge onto a highway.

Thanks for all the suggestions. My plan of attack will be: 1st to re-adjust the fronts and try my best on the rears. I think if I disconnect the drive shaft there may be a better feel at the rears. Next would be re-bleeding and if those fail then a new master (it is pretty old).

[UKcuda]

if it still goes to the floor and you dont have a fluid leak replace the master cylinder

I also agree it sounds like it could be a seal is going bad in the M/C.  Once it seals the pressure holds it out against the bore so it seals fine then and doesn't creep down.  A clue is they sometimes do it worse when they are cold so if it seems to get better after driving for a while then probably it's a seal.

[tman]

After your note that the m/c is "old", that is most likely the problem.  The next thing is to check rubber brake lines.  When they get real old, they expand like a rubber hose that is about to burst under pressure.  The hose itself is failing if that is happening.  Don't cut corners, it is your life and car you are saving.  M/C and hoses are cheap insurance and not that expensive.   

[Road_Runner]

My vote is master cylinder too.  I've had a couple go out in the Roadrunner through the years and the first sign of failure was this type of behavior.  It's cheap insurance just to go ahead and replace it because I came very close to rolling through a busy intersection years ago when I didn't immediately replace mine after it went to the floor the day before.

Later, Jim