Turbo6

Putting the valve in the rear main line doesn't make sense though if what that article states is true. If you think about it, with larger front "more efficient" brakes, you decrease the effective line pressure in the rear at lock-up in the front, but if you put the valve in the rear main line, you can't increase the rear line pressure above that initial amount, because with the valve 100% open, you still aren't routing any more fluid pressure to the rear than you were before you installed it and had the mismatch. So, you don't fix the problem. You would need a way to route addition fluid FROM the front TO the rear to get bias back to the correct 80/20 or whatever ratio you are shooting for since even with an unimpeded line, you aren't getting enough pressure, a valve that restricts will only further exacerbate the problem? No?

Injuneer

The brake proportioning valve is used to reduce line pressure to the circuit it is installed in. It can't increase pressure. Any pressure gained through velocity head in the restriction orifice is lost when the fluid enters the full-diameter brake tubing.

Some examples:

From the description of the Wilwood #2220 proportioning valve:

From the description of the Tilton #3528 brake proportioning valve:
The 4th Gen F-Body has an excessive braking force capacity in the rear. The rear braking system is capable of generating braking forces that significantly exceed the capacity of the tire to apply that force to the road. This is a result of the fact that the 4th Gen is already approaching a static front wheel weight bias of almost 60/40, and made worse (maybe 80/20??) by the amount of weight transfer to the front under deceleration. You want to reduce the rear braking forces until they are less then the product of the vertical weight loading to each rear tire X the coefficient of friction of that tire. Notice that typically, the rear pads wear out 2X to 3X faster than the front pads.

You aren't trying to increase the braking force at the rear.... you are trying to limit the braking force so it is less than the limited tire/road interface capabilities.

Bone Daddy

Just noticed the mistake.. doh! edited. Thanks again Injuneer.


[edit] And now the post is gone? Okay, from now on I'm slowing down when I post, multitasking on multiple forums is messing me up. Not only causing multiple edits, but it's hell on my IE.

OBE1 95Z28

Based on Inguneer's input, then the installation of a larger brake system in the front will help to offset GM's factory bias towards "over braking" in the rear. How is the factory bias generated? Is their a proportioning valve that can be replaced with an adjustable one?

Bone Daddy

The factory bias (still hate using that word) adjustments are made by the master cylinder's compensator and the ABS modulator. There is no other current way to adjust the factory bias, other than adding a aftermarket proportioning valve to the system, or to do as I and other's have done, and delete the ABS system all-together.

OBE1 95Z28

Thanks for the quick response Bone Daddy. I guess you could add an adjustable valve to both the front and rear lines and dial it in that way.

Bone Daddy

Possibly, but I don't know what effect that would have on the ABS system as a whole. As far as I know it's never been tried. People usually add a PV to a line if aftermarket brakes or do a drum to disc swap is done. Might be an interesting project though.