If you do a rear disc brake conversion on your Fox body Mustang, you will more than likely have to install a manual proportioning valve. The stock proportioning valve is setup to provide the correct pressure for the stock drum brakes, and is pressure based. An adjustable aftermarket proportioning valve is usually based on volume, and you can fine tune the brake bias to your preferences.

The hardest part to installing a manual proportioning valve is rounding up the parts. Below is a list of the parts you will need, as well as where to get them.

• Ford Racing Performance Products Plug (FRPP part number M-2450-A)
• Wilwood Adjustable Proportioning Valve (Summit Racing part number WIL-260-2220)
• Teflon tape
• DOT brake fluid

You will have to gut the stock proportioning valve. Refer to pictures 1 and 2 on the right for the location of the valve. Once you have located the valve, you will need to remove the nut on the end of the valve facing the front of the car (picture 2). This is the side that controls the rear brakes. Be careful in taking that end nut off - there's a spring in the valve, so it will shoot out, along with a rod. The parts that you are supposed to remove from the stock valve are shown in picture 3. Once you have removed those pieces, replace the stock end nut with the FRPP M-2450-A plug (picture 6).

Now that you have the stock prop valve gutted, you can install your new manual prop valve. On the passenger side next to the firewall, there is a rear brake line that has a coupler in it. This coupler is just about the same width as the Wilwood manual prop valve. (See picture 5.) Remove this coupler, and intall the manual prop valve. Make sure you install the valve so that the flow is correct - in and out on the valve corresponds to the the flow of brake fluid from MC to rear end.

Once you have correctly installed the new prop valve, you are ready to bleed the rear brakes. It will more than likely take a while since the line was opened pretty close to the MC. After the brakes are bled, it's time to go adjust the brakes. Here's how I did it: I found a large empty parking lot which I visted after dark. I got up to abotu 30mph or so, and really laid into the brakes. Rears didn't lock up, so I popped the hood, increased the pressure to the rear, and repeated the process. You want the rears to lock up around the same time as the fronts. It is kind of hard to tell on pavement, so I later found a gravel road and got a friend to stand outside and watch the wheels to see when they locked up. He said the rears locked just a hair after the fronts, so I decided I would leave it at that. I'm sure I could get a little better performance from it, but I haven't felt like adjusting it any more.