proportioning valve effectiveness - was monkeylads

[Bernard Littau]

> That's right there is only one channel going to the rears!  I am
> enlightened!
>
> Now taking this one step further (if you don't mind) ...
>
> Just how effective (accurate?)can the proportioning valve be?
> My first experience with a proportioning valve was on my 82 Toyota 4X4
> where
> I had to make some modifications because of the lift kit I installed (2"
> lift)  I learned a bit about the system then and I recall thinking this is
> pretty goofy.  Under braking, the relationship between the body and the
> axle
> changes due to the nose of the vehicle dipping and I guess the rear
> lifting,
> which activates the lever and reduces the brake fluid flow to the rears so
> they don't lock up.  Seems pretty imprecise.  Looking at the valve on my
> 5ktq, it isn't a whole lot different in design than the toyota.

Way more accurate (and precise :-) than you might think.

Given the standardization of the parts and the predictable behavior of say,
the brakes, the lever length and spring rate are very likely to be
specifically tuned for each model of car.

Consider distributors of tens of years ago:  Ignition advance was done
mechanically through centrifugal force (rpm) acting on lobes and springs on
an eccentric cam gear.   The advance curve was specific to the application
(car, engine model and target octane).  These curves, and their
reproducibility from car to car, were very good representations of an
optimal advance curve (factoring in some safety margin).

Best,

Bernard