Brake Proportioning Valve, Good bad or ugly Options

[Charles Freeborn]

So, on to the brakes in this new car. It still has the OEM proportioning valve for the rears. As I understand when the brake pressure reaches a certain limit (500 plus psi as I recall) it stops sending fluid to the rear calipers. My first question is does it stop and hold at that psi leaving the rears engaged to that level while allowing fronts to get more input, or does it drop the rears to 0?
The other consideration is to use a manual valve such as the Tilton. If going that route how does one determine settings without chancing spins or other drama?
Thanks.

[GregAmy]

To clarify, both the stock prop valve and the Tilton-type regulators (whether screw or lever) work exactly the same way: they don't "stop and hold at that psi" but they change the rate at which the rear pressure rises in relation to the front.

See attached chart as an example.

Which way you go depends on your needs/desires. As Chris pointed out, you can increase the rear ratio by screwing in the threaded shaft a bit more; what he described is exactly what I did to my street car (per his instructions) to get more rear bias. The factory one is a bit too conservative for my driving, but is safer for the average driver on the street (and in the rain). That's a first step you could start with right now, with about 20 minutes' effort.

If you choose to re-plumb and add a manual valve in the cockpit, you'll remove the factory one entirely and insert the manual valve in a convenient location.

You could, technically, replace the stock one with a manual valve in its place, but brake proportion changes would require you to come into the pits and dive down deep under the car to change it. I'd suggest what Chris describes, and that's mounting it in an easy-to-the-hand location in the cockpit.

As for screw type versus lever? That's your personal preferences. The screw type will give you the option of much finer adjustments versus the 6-position lever.

I personally prefer the lever type because I can reach down and "feel" where I am on the prop valve setting without having to look at it. Plus, the fewer things I can mess up, the better...(IMG:style_emoticons/default/wink.gif) I doubt I can differentiate between 3 notches and 3.5 notches, let alone 3.25 notches.