Brake question

[jaak]

did this part come on only factory disc brake cars? (69 model)

Jason

[resq302]

Yes, that is what was called a hold off valve that went in between the distribution block and the rear axle.  It pretty much delayed the rear brakes engaging a split second after the front discs to prevent the rear brakes from locking up.

[Just 6T9 CHGR]

Installed on a friends 70 GTX which is the same set up IIRC

[Ghoste]

It's probably more commonly known as a proportioning valve.

[jaak]

Thanks for the replies, you see my car has this on it, it also had a bendix dual diaphragm booster. But had front drums, I don't have a fender tag, but I think someone put the drums on it at some point in time, I don't know why maybe parts availablility or something years ago, but Im starting to think that my car was a factory disc car. Im converting to disc anyway but thought that was something cool anyway, so I can use the distribution block and the hold off valve, and not have to plumb in a proportioning valve?

Jason

[Ghoste]

Correct, the hold off valve and the proportioning valve are the same thing.

[TripleBlackGator]

What is this block (arrow) leading to passenger front? Is that needed for a front disc conversion with a non-power system?

[Ghoste]

It's a metering valve and I'm not sure but I think it's function is to improve the ability of the proportioning valve to do it's job.  It is a part of the disc brake setup.

[Musicman]

The Metering Valve, which is often called a Hold-OFF valve, is there to "HOLD-OFF" the action of front disc brakes until the rear drums have had a chance to engage. A Proportioning valve is part of the rear drum brake system... it determines how much and how fast the pressure is allowed to build up in the rear drum system, in accordance with brake pedal action. The "distribution block" your talking about is actually a hydraulic safety switch which isolates the the front and rear brakes systems from each other in the event of a pressure loss due to a leak in either one of the systems.
A word of caution... if you are driving down the road and you hit the brakes, and one of the front brake lines burst, the hydraulic switch will isolate and shut down the front brake system. When this happens, your natural instincts tells you to JAM on the brakes... Bad Idea... The proportioning valve reacts to sudden pressure, and it will effectively isolate the rear brakes after engagement. You will eventually stop, but it will be very slow ride. Using normal pedal pressure, the proportioning valve will not overreact, and you will be able to stop the vehicle a lot faster.

[Ghoste]

I thought the proportioning valve was also a disc brake specific valve?

[Musicman]

Prop valves may be found in any system Disc or Drum, or any combination thereof, but it's only used for the rear brakes, and controlls the rate at which the line pressure rises.

[resq302]

What is this block (arrow) leading to passenger front? Is that needed for a front disc conversion with a non-power system?

According to Inline tube, Mopar had two different line set ups for the disc brakes.  There was one that used a distribution block and that rear hold off valve.  The other type had an in line metering valve before the rear ward hold off valve.  Kind of like a production pressure change or something.  In line repros all of the brass hold off, metering, and distribution blocks now.

[Musicman]

What is this block (arrow) leading to passenger front? Is that needed for a front disc conversion with a non-power system?

The Metering Valve (Hold-Off) for the front disc's.