1968 Dart Proportioning Valve Plumbing? Which lines go where?

[PinkGT]

Hi FABO members,

I'm trying to put the original brake proportioning valve back on the car. I have a vacuum assisted 2 chamber M/C that was powering 4 wheel drum brakes on small bolt hubs. I had a guy switch out the front drums for a small bolt disc brake setup I ordered online and he installed an adjustable proportioning valve which is now leaking. Id like to go back to the old original brass unit which I still have but I want to make sure it is plumbed correctly so the brake light switch works right etc. Does anyone have a diagram from the Factory Service Manual saying which ports are for what lines?

Thanks!

 

[AJ/FormS]

As I recall the front and rear lines have different fittings and so will only fit one way. But if not, then;

At the M/C the frontmost chamber gets plumbed to the rear brakes.
Here is a pic of the guts

 

[PinkGT]

As I recall the front and rear lines have different fittings and so will only fit one way. But if not, then;

View attachment 1715520481View attachment 1715520483

At the M/C the frontmost chamber gets plumbed to the rear brakes.

Thanks for the reply. I dug around in my reprint of a service manual and I think what I have is strictly a warning lamp switch, not an actual proportioning valve! Although all the brake lines do run through it before exiting to various wheel cylinders.

Hijack my own post now: I wonder if I could just get a proper disc/drum style master cylinder and not use a proportioning valve? That way I could reinstall the warning lamp switch and ditch the leaky aftermarket part.

Thoughts FABO folks?

 

[PinkGT]

Thanks for the reply. I dug around in my reprint of a service manual and I think what I have is strictly a warning lamp switch, not an actual proportioning valve! Although all the brake lines do run through it before exiting to various wheel cylinders.

Hijack my own post now: I wonder if I could just get a proper disc/drum style master cylinder and not use a proportioning valve? That way I could reinstall the warning lamp switch and ditch the leaky aftermarket part.

Thoughts FABO folks?

Or is it that all the warning lamp switches also serve as proportioning valves in some capacity? Can anybody clear up my confusion on this one?
Thanks in advance..

 

[my68barracuda]

Or is it that all the warning lamp switches also serve as proportioning valves in some capacity? Can anybody clear up my confusion on this one?
Thanks in advance..

My OE distribution block on my 68 Barracuda is as you mentioned a distribution block that also houses an sensor that lights a dash lamp if the front to rear line pressure differs significantly. My car was a 4 wheel drum car. The block has no proportioning action at all.
When I switched to 4 wheel disks, the mopar 73 and up disks in the front and a Dr Diff disk kit in the rear, Cass ( Dr Diff) said to keep the OE distribution block as it was originally. I did and the brakes are fine. I know my set up is a little different than yours, but this is an example where the OE block works fine.

 

[AJ/FormS]

I wonder if I could just get a proper disc/drum style master cylinder and not use a proportioning valve?

There are only three things that separate a disc/drum M/C from a Drum/drum.
1) the sizes of the reservoirs,
2) residual valves, and
3) the size of the piston.
There is NO proportioning done in the M/C.
If your car has 4 same size tires on it, then you MUST have a P-valve.
And the reason is;
Disc brakes are NOT self energizing, drums are.Therefore;
Disc brakes require much greater hydraulic pressure for the same rate of stoping. This much greater pressure , with no control to the rear, will cause the rears to lock up much sooner. When the rears are skidding, traction is lost, and there is nothing to keep the back end in the back, so it tends slide out sideways and spin the car around. Therefore, the rear drum brakes have to have some kind of brake-force reduction, or increased friction to the road.(Bigger or stickier tires)

Drum/drum systems achieve rear proportioning with reduced shoe size, and wheel cylinder size.

The rear brake system is completely independent of the front. They are just operated by the same pedal. The rear system is actually not even connected to the pedal and is normally operated by a hydraulic connection inside the M/C.
The Chrysler P-valve I showed is actually a C-valve,or Combination Valve, in the which;
The upper portion to the front brakes is just a distribution block.
The lower portion is the Proportioning system to the rear brakes.
The inbetween portion houses the shuttle valve, that turns on the brake warning lamp, when either brake system fails.

 

[67Dart273]

^^And on that note^^ the naysayers claim you must have a disc brake master. When I had mine together, it uses 73/74 Duster front disk, and a Lincoln Versaille disk brake 9" rear. I ruptured the residual valves in the STOCK drum master with NO OTHER changes.

Frankly if guys need a prop valve and have to buy one anyway, I'd use an adjustable aftermarket. Changes in caliper/ rear cylinder size and differences in tires.......................