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Low Hard pedal on 69 Plymouth gtx power drum brakes

B

BADASS 69R/T

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Hi Guys. I have a 69 Plymouth gtx power drum brake car. I bought the car with the problem of a low hard brake pedal that would barely stop the car. So I went and changed the wheel cylinders and shoes. Bled the whole system several times running out all the old fluid with new fluid. So there is no air in system. But still have the same problem. I then checked out the check valvery on booster and made sure that I had enough vacuum to the booster. All was good. The booster even holds vacuum because after I run it I get air out of booster when I removed the check valve. I even replaced the master as a last ditch effort. Still the same problem. Please help.
 
Could you post a photo of the master, the booster, and the firewall adapter plate?

First thing that comes to mind is that the parts you have may be for a disc/drum setup, and that the replacements you have were matched to incorrect existing parts.

Just throwing some ideas out there. Would be easier to see what we're working with though.

-Kurt
 
I was thinking the same thing. Is the rod length different on the back of the booster from a power drum set up to a power disc? I know that the booster is a 10" factory as well as the master is an original with a rebuild kit installed. I will get pics tomorrow. thanks
 
hope i explain this correctly; there's a rod that goes from the linkage on the back of the booster to the brake pedal. those rods were made in different lengths. i think you have a short one and need the longer one to raise the pedal. a hard pedal is probably not enough vacuum or could also be the linkage has been bolted together too tight.
 
BADASS 69R/T said:
I was thinking the same thing. Is the rod length different on the back of the booster from a power drum set up to a power disc? I know that the booster is a 10" factory as well as the master is an original with a rebuild kit installed. I will get pics tomorrow. thanks
Click to expand...

I know that there are different MC/booster firewall mounting plates for non-power drum vs. non-power disc vs. power disc, vs power disc w/426 Hemi; but I'm not sure if power drum uses yet another plate. Some factory power disc setups also use a bellcrank on the pedal rod.

It'd be nice to put together a thread for this and document it visually for once. In fact, I think I'm going to do just that...

-Kurt
 
If the booster is stock original it is probably not working.
 
TxDon said:
If the booster is stock original it is probably not working.
Click to expand...

So far, we don't know anything about what he actually has. That's why we need pictures of the MC, the booster, and the firewall plate.

Guesses at this point are just that, guesses.

-Kurt
 
My 67 GTX has kind of the same issue. The question is, how do the brakes work? Mine seem to stop the car fine and straight with no pull left or right. The pedal on PB cars seems to be about the same as the gas pedal and I believe they were designed that way to allow going from gas to brake without raising you foot. I guess that may mean that people who bought cars with power brakes wwere also deemed to lazy to pick up their foot to move it to the brake.
I chased the same problem, changing wheel cylinders, shoes, brake lines bleeding etc. and then finally gave up. The pedal is somewhat hard for power brakes and the pedal seems sensitive since it has minimal travel. I do have a shorter aftermarket booster. The car stops fine, and I am used to it. I wanted to upgrade to disk brakes initially also, but have changed my mind. I am used to the drum brakes now after having not driven a drum car for 40 years and now they seem a part of the old car feel. You do just learn to leave yourself some stopping room.
 
Have any of you had the brake shoe to drum arch checked or the drum itself checked. Brakes need full contact to work right. This in no way explains a low pedal. Also no one has mentioned actually checking brake pressure. Quite assuming new parts always work.
 
67GTX440 said:
My 67 GTX has kind of the same issue. The question is, how do the brakes work? Mine seem to stop the car fine and straight with no pull left or right. The pedal on PB cars seems to be about the same as the gas pedal and I believe they were designed that way to allow going from gas to brake without raising you foot. I guess that may mean that people who bought cars with power brakes wwere also deemed to lazy to pick up their foot to move it to the brake.
I chased the same problem, changing wheel cylinders, shoes, brake lines bleeding etc. and then finally gave up. The pedal is somewhat hard for power brakes and the pedal seems sensitive since it has minimal travel. I do have a shorter aftermarket booster. The car stops fine, and I am used to it. I wanted to upgrade to disk brakes initially also, but have changed my mind. I am used to the drum brakes now after having not driven a drum car for 40 years and now they seem a part of the old car feel. You do just learn to leave yourself some stopping room.
Click to expand...
Rock hard pedal. No pedal movement. Doesn't stop. Owned multiple b body power drum cars and have never seen or heard of this before. Thanks for your response.
 
Not trying to be a wiseguy, but are the brake shoes self-adjusting, or police-type, manual adjusted only?
 
And do we know anything about what setup is actually installed under the hood yet? Which master and bore? Which booster? Which firewall plate?

Tons of things being taken here at face value as being correct, but there's still a problem, and I don't see anyone getting closer to a solution.

Ignoring the specifics is an easy way to wind up with a brake system that doesn't work in the first place, much less diagnose it.

-Kurt
 
My bet is someone will post something that will turn the lights on and he will know the answer because he read it here.
 
Had to add this in response to Mopar 3 B:

Following are just about all the potential factors that could affect braking performance for a single Mopar (and with a few exceptions, most any other brand of claptrap we love) that is knowingly running four wheel power drums, save any other information about the system presently installed:

  • Firewall adapter type
  • Master cylinder-to-brake pedal pushrod type
  • Master cylinder-to-brake pedal pushrod length
  • Master cylinder condition/quality (condition if used, quality if new)
  • Master cylinder type (reservoir types, residual valve)
  • Master cylinder bore size
  • Master cylinder preparation quality (Was it bench bled properly?)
  • Vacuum booster condition
  • Vacuum booster type (drum or disc?)
  • Brake line condition
  • Brake line routing from distribution valve
  • Distribution valve type (is it a prop valve where a prop valve shouldn't be?)
  • Distribution valve condition
  • Proportioning valve type, condition, and if present, why is it there? It's a drum brake car.
  • Brake fluid condition
  • Brake fluid type
  • Brake fluid possible contamination (by particulates or mixing DOT 3/4 with 5)
  • Brake fluid bleeding - quality of job (Sure all the air is out? Sure you never ran the master dry when bleeding?)
  • Brake cylinder condition
  • Brake drum condition
  • Brake drum contamination
  • Brake drum adjuster condition
  • Brake drum adjuster installation direction
  • Brake drum adjuster adjustment
  • Brake drum hardware direction of installation
  • Brake pad/shoe wear
  • Brake pad/shoe contamination
Of that laundry list of things that can be screwed up, the only things we know are the following:
  • Vacuum booster: New, operational, type unknown.
  • Pads: New.
  • Wheel cylinders: New.
  • Fluid: New, system bled, presumably correctly.
We don't know anything else.

In short, NOBODY is going to come in here out and by magic know the issue with the OP's car - not without a one-in-a-million wild guess, or a lot of expensive WRONG guesses. Experts are not experts because they're clairvoyant, it's because they use a proper checklist of troubleshooting steps. And part of that troubleshooting involves knowing what equipment is installed in the car in the first place. That can't happen by guessing when the details are this vague.

-Kurt
 
Just for grins...since it's been said, the car already had the problem. Do the basics, meaning does it have the correct parts?
Drums all around...have the right master? For that year car, master should have two pots, both the same size. If one's big, one small...that's for disc/drum...wrong master.
 
miller said:
Just for grins...since it's been said, the car already had the problem. Do the basics, meaning does it have the correct parts?
Drums all around...have the right master? For that year car, master should have two pots, both the same size. If one's big, one small...that's for disc/drum...wrong master.
Click to expand...

Funny thing, even though I agree entirely on the importance of using the proper master with the residual valve for drum brakes, my '69 Valiant 4-wheel drum car came with an incorrect disc master on it - and since it was the proper bore size, one wouldn't know by pedal feel that the wrong master had been installed.

This is not to say it shouldn't be changed if incorrect, but I'd be willing to make an educated guess that bore size would be more likely to cause an issue than a disc/drum master on a drum car.

-Kurt
 
Only reason I brought it up, is the pistons/ports are different, for brake types.
One thing for sure...low hard pedal...'something' is causing it, probably something simple!
 
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