How To Remove Brake Proportioning Valve?

[Eagle7]

2nd gen RX-7. I've got an adjustable brake bias valve, but never removed the stock proportioning valve - now it's time. There are two inputs from the master cylinder, one labeled "F", the other with an arrow. Two outputs, one labeled "F" to the RF caliper and one labeled "R" to the rear.

I've taken one of these proportioning valves apart. There's a sliding "spool" that uncovers an opening to the rear line, with a spring holding it closed. If I've got it figured correctly, pressure from the front overcomes the spring pressure.

I seems like the easiest way to "remove" the proportioning valve is just to gut it - remove the spool and spring. That would turn it into a manifold connecting the four lines. Is it OK to apply "F" line pressure to the "arrow" line, or do I need to separate the front and rear circuits? If so, I expect I need to connect the "arrow" line to the rear.

[Rabbit07]

Marty,

the purpose in multi circuit brakes is safety. If you loose one circuit, you can still stop with the other. All US cars required them to be multi circuit around 1965.

[tom91ita]

is it possible to keep the dual diagonal braking and add two front - rear bias valves? one for each "diagonal" front to rear?

i like the idea of the safety of the diagonal plumbing............

[Spinnetti]

The normal method for this is really simple, and still keeps dual circuits, just not cross biased.

1. Take out the prop valve.
2. The front circuit goes from the master to a "tee" which then feeds both front brakes
3. The back circuit (single line from the master) goes to your "pressure limiting prop valve), then to the back of the car, where it too gets a "Tee" which goes to both rear brakes.

The result is, you have two lines teed to the front circuit, and two lines teed to the back circuit of the master with your prop valve in there. Now, test it under threshold braking, and adjust until the rears lock under FULL braking. Once you get that, back it off a touch, and bingo - you are done :)

[dickita15]

Gutting the tee would be bad. If one line breaks you could lose all braking. If I am not mistaken the left front is powered directly from the MC. If I am right you can just remove the prop valve and use a coupling to connect the rf line to the front line from the MC and another coupling to connect the rear brakes to the rear line from the MC or run a new line to do the same thing without couplings.

[Dano77]

The easiest way is also the cheapest. Disconnect both inlets and both outlets. Take a pair of 3/16 or Metric flare unions NOT compression fittings, And connect and bleed system. The end result will be max braking front and rear so you need to add a pressure limiting type bias valve in side the car. Done
Dan-o 70 IT7

[Eagle7]

Got it. Thanks very much.