proportional valve mechanism

[Bernard Littau]

> I don't have much resonse on my question about proportional valve rod
> (or pin) length of travel. So, I am trying to ask different question.
> Does the valve change the pressure (really)  proportionally to load or
> it has just on/off states (for example, on 1:1, off 5:1 ).  Again, the
> rod travels only 1mm  and I don't believe it is right.  But if it on/off
> switch then it might be ok.  Frankly speaking, I don't believe it works
> lke switch but, from other hand, I don' t see how it can seize. There is
> no rust inside. Unless something is dislodged inside...  Any BTDTs?

I am not claiming I know how it works for sure, but my sense is that the
proportion is mediated by the spring that attaches the lever to the
trapezoidal arm.  The spring is an important part of the valve's function.
As the rear wheel moves away from the car (down), spring pressure on the
lever is increased, and proportionally less brake pressure is allowed to
activate the rear brakes.

I think the general idea is the pin is normally closed, and opens just
enough to allow some brake fluid to pass to activate the rear brakes.  The
1mm of travel didn't bother me when I had mine out.

It seems that the one we have is a dynamically adjusted version of what this
guy is talking about making:
http://members.aol.com/dvandrews/bpvalve.htm

I can't figure out how our proportioning valve does what I think it is
supposed to do :-)  I guess the thing works because the rears are on one
"pump" and the fronts are on another "pump" in the master cylinder, and
these proportioning valves somehow introduce a difference in volume or
pressure between the two closed systems.

Puzzled, but trying to think,

Bernard Littau
Woodinville, WA
'88 5ktq