Brakes Staying On

[JedIEG]

I am out of ideas with this. On my dad's '74 Cuda, the brakes will stay on when you press the peddle. You have to lift up the peddle with your foot to get it to come off. Parked at idle the peddle hangs up a little so that the lights are on, but going down the road it keeps them on enough that there is drag on the car. It is originally a front disc car, that we upgraded with SSBC rear discs years ago and this was always a problem. (It made learning to drive a stick a real treat). Also swapped from an auto to a 4 speed.

We have tried everything. New master cylinder, new master cylinder with the residual pressure valves removed, bleeding the system, adjustable proportionally valve, a return spring on the peddle, and most recently a cardon reman brake booster...
I am open to any ideas on what's wrong and how to fix it.
Dad wants other people besides me and him to feel comfortable driving it.

 

[Ron H]

How much playing was required, if any was done, with the pedal linkage adjusting? This can be a number of things (as I found out after a brake conversion including from manual to power). Seems elementary; but make sure the pads are not binding in the calipers watching them with a partner applying and releasing the brakes. Could be a bit more deburring and lubing the guides is needed.

Other thing with the pedal adjustment, make sure there’s no ‘pre-charging’ going on with the booster. This is pedal linkage adjustment. A bit of ‘free-play’ is necessary for the pedal in its home position. This can cause pedal-sink down. You may want to check the MC to booster ‘gap’ if you haven’t, using a booster gap gauge, this makes this an easier chore. Is your ride built up, such as hotter cam? This can create issues with ample vacuum for the booster, I think around a minimum of 17-inches is necessary for most power brakes. Of course, I figure you've checked all the vac hoses, connections, and valve.

 

[ckessel]

Where did you get that gauge?

 

[Ron H]

Where did you get that gauge?

I bought it a few years ago online as the auto stores I checked didn't stock them, at least then. They're on Amazon for dirt cheap...lol, think I paid more for this one back when! How can this be possible?

 

[ckessel]

What is it called? Disregard, just found it. Thank you.

 

[Black_Sheep]

I second what Ron H says. If the push rod from the brake booster to the master cylinder is too long, it will cause the brakes to hang up. Do you know if it’s all the brakes hanging up or the fronts or rears? If it’s all four, I would definitely check the booster pushrod adjustment.

 

[Ron H]

Another couple cents for the OP in case you haven’t come across it: The MC bore size is different for manual and power brakes; doesn’t sound applicable if you already had power brakes, nor would the pedal ‘ratio’ – things I encountered with my conversion. Also sounds like you have pretty much installed all new components. If no, the rubber lines age, they can balloon under pressure and collapse. Something I’ve come across, once. Buddy had this issue on his front lines. Assume you had bench-bled the MC, if there’s air trapped in the MC, line bleeding only won’t get it out. Other thing is to recheck your install A to Z case something was overlooked.

All stuff you likely already know, but just tossing out some ills I’ve come across, learning a few the hard way; seems like it could be the rod adjustment or possible pad hang up, least it was with mine.

 

[Kern Dog]

If the brake PEDAL is rusty where it swings from the brackets in the dash frame, it will hang up. This happened to me with a 72 Duster that sat in a field for 10 years before I got it. Both the clutch and brake PEDALS would hang up and drag. I had to replace the whole set to get it to work right. Now I’m of the mindset that sand blasting and/or Evaporust could have saved the rusty stuff.
If need be, you could modify a clean automatic car brake PEDAL by cutting it down to the smaller size.

 

[BigFlo]

Looks like the ‘peddle’ really hit a nerve