'73 Swinger brake drag

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Brettbot

Brettbot

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Hey guys, looking for some advice. I recently picked up a '73 Dart Swinger as my first classic car. It's got manual brakes, disc front drum rear. I believe the previous owner changed the original front drums to discs, but I don't know that for sure.
When I took the car to get it inspected, the mechanic warned me that the brakes were dragging and would eventually burn out the rotors, but I wanted to try and fix it myself.
My Father in Law and I replaced the calipers in front, changed the soft lines and brake fluid, and bled the brakes, but they still seem to be dragging. I took it for a quick 2 minute drive around the block, and the rotors were already hot to the touch.
The master cylinder looks like the right one, 2-chamber "small front, big rear" style. What should I look at next? Proportioning valve? There's no way to adjust the calipers/pads so that they have standoff from the rotors, is there?

vbficnu.jpg
 
Usually the front hoses are the primary culprit if the front brakes are dragging, and just because they’re new doesn’t necessarily mean they’re good, the quality of rubber and production on those front hoses has really taken a dive.

I’m assuming if you changed the calipers and hoses that you also flushed all the old fluid out and bled the brakes? If you didn’t to the rears that’s another thing to do, I would make sure I bled everything until the fluid was clear at all 4 corners. The other thing is that the factory prop valve is self adjusting, you bleed the brakes in order to reset it - passenger rear, drivers rear, passenger front, drivers front.

Assuming you have the right proportioning valve on there, can you post a picture? If the car was originally drum/drum it would have come with a distribution block, not a prop valve.

It’s also possible that the master cylinder isn’t right, and it has a residual valve in the port for the front disks. If that’s the case, the residual pressure will cause the disks to drag and the residual valve must be removed. You can do that by just threading a drywall screw into the port and pulling it back out, you should pull a small rubber seal with it. There’s a picture somewhere I’ll try to find and post.
 
72bluNblu said:
Assuming you have the right proportioning valve on there, can you post a picture? If the car was originally drum/drum it would have come with a distribution block, not a prop valve.
Click to expand...
IMG_20220923_130432.jpg

I believe this is the proportioning valve, right?

72bluNblu said:
It’s also possible that the master cylinder isn’t right, and it has a residual valve in the port for the front disks. If that’s the case, the residual pressure will cause the disks to drag and the residual valve must be removed. You can do that by just threading a drywall screw into the port and pulling it back out, you should pull a small rubber seal with it. There’s a picture somewhere I’ll try to find and post.
Click to expand...

I appreciate the reply! I'll take a look into the residual valve when I get the chance.
 
Brettbot said:
View attachment 1715993671
I believe this is the proportioning valve, right?



I appreciate the reply! I'll take a look into the residual valve when I get the chance.
Click to expand...

Yep! That’s the prop valve and it looks like the right one for a disk/drum car.

That front brake line coming off the top right looks pretty beat up, that could be an issue as well.

The residual valve shouldn’t be there on a disk/drum master cylinder, but stranger things have happened when stuff gets swapped, replaced or rebuilt.
 
Your picture is not a proportioning valve, that is a distribution block. No "proportioning" occurs here only "distributing". The original proportioning valve is located somewhere between that block and the rear end. I agree with#2 in that you should check the M/C for the presence of the residual check rubber which disc brakes should not have.
 
Murray said:
Your picture is not a proportioning valve, that is a distribution block. No "proportioning" occurs here only "distributing". The original proportioning valve is located somewhere between that block and the rear end. I agree with#2 in that you should check the M/C for the presence of the residual check rubber which disc brakes should not have.
Click to expand...

Yeah actually that’s a factory proportioning valve. You can see one here at DoctorDiff
Mopar 1 Piece Proportioning Valve

F4A8D208-9635-40B8-AF24-04F1DBB24A52.jpeg


This is the distribution block
Mopar 1 Piece Distribution Block
5999B5DD-AB3F-4A9E-A3EB-22F6A36ACE08.jpeg
 
Well, I think I've found the problem, I'm just not sure how to correct it. The pads are always touching the rotors because the space between the pads is exactly the same as the width of the rotor! As I said, we replaced the calipers so I know those are correct. Who knows what the Previous Owner did, but obviously something is wrong... Any way to tell what's going on without just buying new correct pads and rotors to compare?
 
Are the pistons all the way retracted in the calipers? Could be an issue with the piston seals or caliper bores.

A digital caliper on the rotor will tell you if it’s the rotor, kinda doubt it’s the rotor.

On a disk brake the only thing that retracts the piston is the flexibility of the piston seal, outside of that it’s just the spinning rotor knocking back the pads.
 
There are a few things that can cause this, at least some of which has been mentioned

1...The caliper pistons "help" being retracted due to the seals, which "walk" sideways and are supposed to spring back. So corroded calipers/ pistons, sticky, gummed up, or deteriorated / old caliper seals could cause this

2...If the master DOES have a residual pressure valve in the disk circuit, that might be a factor. The disk/ front brakes connect to the REAR port on the master

3.Someone mentioned hoses, but if the entire system is old, there may be restrictions. I would start by flushing it out.

4...Something could be gummed up in what IS your proportioning/ combination valve, as it IS a prop valve and also acts as a distro block and warning lamp switch. This is a piston that shuttles to activate (ground) the switch terminal

5..Make certain the master piston(s) are fully returning and not blocking pressure. You can see this by having someone manipulate the brake pedal while watching the fluid in the master. There should be small "spurts" of returning fluid on let-up in both halves of the master

All of these drag "some." All of these run "somewhat warm"
 
Well like I said, the calipers are brand new and the pistons are pushed in until they're flush, so I don't think that's it.
The smaller front of the master cylinder (marked R) goes into the bottom right on the proportioning valve, and the bigger rear (marked F) goes into the top of it. That's correct according to the diagram.
Is there not supposed to be ANY gap between the pads and rotors? How do you judge if they're dragging or not?
 
There will be "some" drag. They will run "warm." But they should not be blistering hot. Jack up a wheel. How hard is it to turn? My memory is that they won't "spin" freely with disk brakes but if you give it a fair shove they might continue for 1/4, 1/2 turn but likely not much

One thing you might do is soon after you apply the brakes, AKA inside of a couple minutes, crack the fitting up at the master for the front brakes and see if there is any pressure
 
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