This post covers installation of the Wilwood Brake Bias Proportioning Valve part number 61-1700 (left image)
If installing the full Brake Bias Combo part number 61-1720 that includes an extension cable (right image), follow these same instructions for the proportioning valve but point the valve towards the firewall and drill a hole in the firewall for the extension cable to pass through in order to mount the knob in the interior of the car.
Before you begin:
- Make sure that you have rags/towels handy to soak up the brake fluid that gets spilled during the install.
- The Wilwood proportioning valve comes with two standard-thread adapter fittings packaged along with the valve. The Miata brake lines are metric, so these do you no good. Discard the standard-thread adapters and use the metric adapters that we supply.
1) Install the metric NPT to flare adapters into the proportioning valve. Be sure to use a closed end wrench as an open-ended wrench can deform the fitting. Tighten to snug, but don’t over tighten them, it is possible to damage the brass fittings. These are tapered fittings and will not bottom out like normal bolts do.
2) Remove the brake lines leading to the stock proportioning valve. Use a 10mm flare wrench so that you don't round off the nuts. Fluid will begin at this point so place rags underneath the area to soak that up. Take note of which line is for the front and which is the rear - the stock valve is labelled F and R.
3) Use a 10mm wrench to remove the bolt securing the stock proportioning valve to its bracket.
4) Use the union fitting included in your kit to connect the two front lines together.
5) Install the proportioning valve in-line with the rear brake line. The side labelled “in” should be attached to the lower line running to the master cylinder. The side labelled “out” goes to the line that runs across the top of
the firewall. Place a wrench on the adapter while you’re tightening the stock fitting, to ensure that nothing is damaged.
6) You can leave the valve floating in space, just mounted to the lines. This will not damage anything. Or, you can use the factory mounting bolt to hold the valve in place against the factory bracket.
7) Bleed the brake system. This is easiest if you turn the knob as far away from LESS BRAKE as
it will go - ie, screw it in (clockwise) all the way.
Once your new valve is installed, set it to use as little rear brake as possible. That means turning
the knob towards “LESS BRAKE” (counter-clockwise). Find a deserted area where you can test safely, and start dialing
in more rear brake until the rears start locking earlier than the fronts. Now go back so the fronts lock
first. Remember, the ideal bias will change depending on the road surface, tire selection and even the
weather, so be prepared to change it if you’re right on the edge.