Brakes drag unless pedal too high

[daytona kid]

I noticed that my 68 charger's front disc conversion brakes are dragging and maybe the rears are also. Without any pressure on it, the weight of the pedal arm is applying a tad of brakes. I had the car jacked up and had trouble spinning the front wheels. Then pulled the pedal up a bit with a bungee and no brakes dragging, front wheels spin easier. I could just put a spring on it somewhere but the pedal will be too high. Anyone ever had this problem? My charger came with power drums and I went to manual disc, reusing the same pedal, brkts, and other parts. So something isn't right, not sure what, maybe the master cylinder piston rod is too long? Do I need a different pedal arm? Any ideas?

 

[dadsbee]

Linkage must be wrong, as the brake pedal should be a toe lift off the accelerator and onto the brake... without even lifting your heel .

 

[Mike67]

To much preload on the MC need an adjustable push rod

 

[Demonic]

It's either one of the two above, or maybe both! I converted my 69 years ago, from power drum to power A body disc, and had no issues. Hopefully someone who has done a like conversion will reply.

 

[daytona kid]

After I got under there and looked I can see where I bent the brake signal switch brkt so it would work with the push rod I got somewhere, probably ordered the wrong one. Just guessing it appears to be about 1 in too long. Anyone know how long it should be?

 

[ckessel]

Measure the depth of the hole in your old master and compare it to the new one. The hole being where the pushrod goes. There could very well be a difference between them requiring you to adjust the pushrod to compensate. It may be putting enough of a load on the piston to get pressure going and not let it off. Several years ago I put on a master cylinder for an AMC Scrambler. Was SUPPOSED to be correct for the car blah blah blah. It was not. Pressure would not back off due to the piston being pushed in. Had to pull it back off. Did some measuring and found that there was a difference in the hole depth between the two pistons. This car was a pain to do a master on. You have almost zero room back there to get to fasteners. Had to pull the hood off, back off the booster to firewall fasteners[ one flat of the nut turn at a time] to pitch the booster sideways some so you could get at the nuts on the master. All of this was by using multiple wrenches with different angles etc, turning by hand.

 

[daytona kid]

My car was missing a lot of stuff when I got it like the old m/c. The one I bought is a Right Stuff and they make an adjustable rod which only adjusts out to 6in. So I'll either order one of those or cut this one off 1in or so.

 

[threewood]

My Dr. Diff disc break kit master cylinder didn't hold my pedal up all the way. I made a spring bracket to hold it up. No dragging issues.

 

[daytona kid]

My Dr. Diff disc break kit master cylinder didn't hold my pedal up all the way. I made a spring bracket to hold it up. No dragging issues.

I may copy your idea there. Where did you get that spring? and about how long is it? I think I remember seeing that pic before. Back a couple of years ago when I started piecing my brake pedal & m/c setup together. Funny I've been driving this car with the brakes dragging for a while, and racing,. wonder if it'll go faster passes now.

 

[threewood]

I may copy your idea there. Where did you get that spring? and about how long is it? I think I remember seeing that pic before. Back a couple of years ago when I started piecing my brake pedal & m/c setup together. Funny I've been driving this car with the brakes dragging for a while, and racing,. wonder if it'll go faster passes now.

I measured the length I needed and picked one up at Tractor Supply. The plate that holds the steering column on, I drilled a hole mounted a bolt with a spacer up top to hold the spring. Eye bolt would work as well.

 

[RemCharger]

My charger came with power drums and I went to manual disc, reusing the same pedal, brkts, and other parts. So something isn't right, not sure what, maybe the master cylinder piston rod is too long? Do I need a different pedal arm? Any ideas?

View attachment 1058461

For starters, the power and manual brake pedal are different. Holes in a different spot for leverage and travel. But in the current configuration, I would check that the brake light switch is not holding it (loosen it off). You didn't mention which master cylinder you have

 

[daytona kid]

For starters, the power and manual brake pedal are different. Holes in a different spot for leverage and travel. But in the current configuration, I would check that the brake light switch is not holding it (loosen it off). You didn't mention which master cylinder you have

Post #7--M/C is a Right Stuff.. And Yep, I read about the different pedal arms during my researching this deal. That's why I asked "Do I need another pedal arm?"., Since mine was power brake but now not. I think there is a difference also in where the brake pedal is as far as height on 4spd and manual trans cars.
Brake light switch was not causing any problem, that was one of the first things I checked... I'm fairly confident that an inch off the length of my push-rod and maybe a return spring like threewood's, if needed then, and all will be well. I'll report the outcome in a day or so.

 

[RemCharger]

Sorry I missed some of your info you posted,, Another question would be -is the new m/c 4 bolt mount? Or did you use the conversion spacer? Just for laughs you could back the nuts(bolts) off the m/c and see if it gets better

 

[RemCharger]

I just converted a 66 single pot to a newer dual circuit and interestingly enough, it had a factory coil spring that went where the rubber boot goes. A return coil if you will.

 

[daytona kid]

I'm going to just shorten the rod before anything else. As I said I'm confident that will do what I need. Will post results.

 

[daytona kid]

I ended up shortening the rod about 5/8"., and readjusted the switch. Works great now, no more brake drag, and pedal is lower. It's now where I can get my foot on it without lifting my heel, like dadsbee said. Made sure I got a really good weld on it after cutting it off.
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