Proportioning valve ?

[Eichorst69]

I have noticed that there are two different style disk/drum proportioning valves.
One valve has two lines in and two lines out.
The second valve has a fith line at a 45 degree angle.
What is the fith line for on this style proportioning valve?

Rob

[Eichorst69]

Ok, I think I figured out the answer to my question, but now I have a different question.

The fith line at a 45 degree angle at the top front of this style valve I guess is a second front brake line!

My question is. Why does one style valve have only one line coming out at the bottom that goes to the front brakes and the other style valve has two lines coming out to the front brakes, one at the bottom and one at a 45 degree angle at the top front when they are both disk/drum proportioning valves?

Rob

[stope4]

Somebody else can chime in, but I think the valve with the extra hole is for 73 and up pickup. When you buy new today, some vendors tell you to plug the extra hole. It does work with 71/72 trucks but not original.

[Eichorst69]

Thanks. I have noticed that most of the 67-72 catalogs show a disk/drum valve with the additional fith hole and I was begining to think that it must be able to be pluged or connected with a tee to the other front line.

Rob