I know the Z brake proportioning valve adjusts pressure to the brakes, but how does it actually work? If you took it out would you get more pressure to the fronts or the rears?

Generally speaking a proportioning valve is used to reduce the pressure to the rear brakes to prevent premature rear wheel lockup. Regarding your question about removing the proportioning valve, you would be increasing the pressure to the rear wheels. Actually the pressure (without the valve) would be the same for the front and the rear.

what 240zx said.

in my case, i have the following setup:

front:

15/16 MC

toyota s12w 4 piston

vented rotors

rear MML swap:

240sx calipers

300zx rotors

I have a wilwood prop valve that I plan to use in line with the rear brakes. What I did is remove the stock prop valve (valves if you have a 73/74), get a T brake line splitter from a 280zx (it's in the front on the driver's shock tower) and run a direct line from the MC to the splitter, and directly to the front brakes. Then install the wilwood prop valve inline for the rear brakes. Voila!

So why can't you run a direct line from the MC to the rear brakes with an inline balance adjuster?

that's exactly what I'm doing. Running a rear line from the rear MC plug straight to the rear brakes with a prop valve inline

Another nice feature of an adjustable proportioning valve is being able to change the front to rear bias. For example...when its rainy out you my want a little more front bias for safety reasons and in the summer you may wish to improve overall braking by adding a little more rear bias when traction is better. Or if you may choose to spend a day at the track or auto-x where you will likely adjust for more rear bias than you would typically use for the street. Anyway, its all about getting the best braking for the conditions you are driving in.

With the 280ZX having 4 wheel disc, has anyone used the ZX proportioning valve when converting to rear disc in a S30?

Auxilary,

"What I did is remove the stock prop valve (valves if you have a 73/74)"

Are you referring to the 3 way valve in the rear of car as the second valve? Why does this valve need to be changed? Does it hold back pressure on the rear brakes?

Skip

early 260Z

I just don't want to deal with the excess of lines and plumbing going all over the place.

The 73/4 have some weird setup where the front MC line goes into a prop valve, that in turn splits into 2 lines to front brakes and then goes to another prop valve that goes to the rear.

They're not adjustable, and I want to have the ability to adjust. Another reason for taking it out is difference in required pressure for 240sx calipers vs. stock drums.

I don't know of anyone using a 280zx prop valve for a rear disk swap, first I've heard of it?