Brake Proportioning Valve Installation

Last updated: February 10, 1999

Date: Tue, 9 Feb 1999 20:24:54 -0500
From: "Rob Robinette"

How to Install a Brake Proportioning Valve
(or a Brake Line Lock or Brake Pressure Gauge)

Note: The web site "How To" has a picture of the installed valve

Why you might need a brake proportioning valve A big brake upgrade will give your front brakes more leverage (larger diameter disk = more leverage) so when you hit the brake pedal the front brakes will lock up before the rears. The anti-skid system (ABS) will help mask this problem by pulsing the front brakes until you apply enough pressure to cause the rears to hit ABS. This is not optimal though, it is better for the rears to begin skidding just before the fronts do. With a proportioning valve you can reduce the brake pressure going to the front brakes so that the rears lock up first. You just insert the valve into the front brake line and then dial down the pressure. Summit racing and Jeg's sells several proportioning valves. The Wilwood unit that I used was $39.95 and will reduce braking pressure up to 57%. A brake pressure gauge will install the same way as a proportioning valve.

What's a Brake Line Lock?

A brake line lock will install the same way a proportioning valve does. A line lock allows you to apply pressure, hit a switch that will hold the pressure, release the brakes and the front brake pressure remains locked but the rears are free for a burn out--Saturday night fun!

What You'll Need for the Install:

Proportioning valve (Summit Racing $40), small metal pipe cutter (for 3/16 inch line, Home Depot $7), pipe double flare tool for 3/16 inch pipe (Pep Boys $40), two 3/16 inch inverted flare nuts (Pep Boys $4), a file, sandpaper, sharp knife and brake fluid.

How to Install the Valve

Don't install a proportioning valve yourself unless you are a very competent mechanic. A single point failure in the brake system will result in the total loss of brakes and possible damage/injury/death! A brake shop can install the valve fairly cheaply.

  1. Before you remove any of the brake line fittings, carefully clean all around them, so that dirt can't get into the system as the fittings are opened. The RX-7's brake lines are 3/16 inch (or the metric equivalent).

  2. First you have to identify the front brake line. There are two lines coming out of the master cylinder. The inside line (closest to the master cylinder) is the front line. You can install it at the master cylinder like Fritz McKeller or you can do what I did and put it near the ABS control unit in the right rear of the engine compartment (in front of the passenger). There's more room there for the valve. To identify the front brake line at the ABS follow the front line from the master cylinder over to where it connects to the ABS box.

  3. You will need to cut out enough brake line to allow your proportioning valve (or line lock or pressure gauge) to fit into the line. My valve said it needed one inch but that didn't count the 1/8 inch NPT to inverted flare adapters that went on each side of the valve. I actually needed to remove about 1 1/2 inch of line. Install the NPT adapters that came with your valve and then measure the width of the unit to determine how much line to cut out. I wouldn't recommend trying to use a hack saw to cut the lines. Unscrew the brake line you are going to cut so you can gently bend it up enough to rotate the pipe cutter. Plug or cover the exposed pipe fitting to prevent debris from getting in. Cut out the length of pipe where the valve will be inserted. After you cut the line you will have a short pipe that you can work on first to learn how to remove the plastic coating and flare the line. It will be a little harder to do the same operation to the line on the car. The brake lines have a protective black plastic coating that will have to be removed before the 3/16 inch flare nut will slip over the line. You will need to remove about 1 1/4 inch of the coating on each tube end so you will be able to slide on the flare nut far enough to allow the pipe flare tool to grip the pipe. After you cut off the coating you will have to use sandpaper to remove the thick green paint and adhesive that's below the black coating. Once you can slide the flare nut on the tube enough to get the flare tool clamp on you're golden. Put the inverted flare nut on so it will thread into the proportioning valve.

  4. Follow the directions to use the double flare tool. Basically you will need to file off the outer edge of the pipe and use a deburring tool (or a large drill bit) to remove any rough edges to the inside of the pipe. [REMEMBER TO PUT THE FLARE NUT ON BEFORE YOU FLARE THE PIPE OR YOU WILL HAVE TO CUT OFF YOUR NICE NEW FLARE AND START OVER!] Put the flare tool's pipe clamp on using its 3/16 inch hole, expose the required amount of pipe, clamp it down, attach the 3/16 inch adapter, screw it down on the pipe, back it out and remove the adapter, then finish the double flare by screwing down the flare tool into the pipe. It's easier than it sounds, just follow the directions. Repeat for the other brake line end. If you screw up the brake line you can buy pre-fabricated 3/16 inch brake lines of various lengths at an auto parts store, you just have to bend them to fit. They are pre-flared and have the flare nuts already installed.

  5. Blow some WD-40 or other solvent through your short line and then blow compressed air through the line to dry it out. Push the brake pedal a little to flush some brake fluid through the line coming from the master cylinder-this must be done to remove any debris that got into the line during cutting, sanding and flaring.

  6. When you install the valve make sure you get the in and out ports right. The in line goes to the master cylinder and the out line goes to the ABS. Make sure the valve isn't rubbing against any other brake lines. If you install it at the master cylinder make sure it won't make contact with the hood.

    Warning: You must torque the brake line fittings to 113-190 inch pounds! (about 10-15 foot pounds) If you don't you run the risk of having a fitting come lose and dump all of your brake pressure which will result in total brake loss! (The parking brake may still work)

  7. After you get it installed you'll need to bleed the brakes. See the bleed_brakes how to.

  8. After bleeding the brakes apply firm pressure to the brakes for about 30 seconds and then check for any leaks at the valve or its fittings. Be sure to go easy on the brakes until you are sure they are working properly. To adjust the bias you'll have to do some test braking. You can remove the ABS fuse to make it easier to figure which brakes are locking up first. It helps if you have an observer by the side of the road that can watch your wheels lock up. Start with the bias valve set to zero pressure decrease and slowly decrease the front brake pressure. Set the valve so the back locks up just barely before the front.


    Date: Wed, 10 Feb 1999 16:50:07 -0500
    From: Sandy Linthicum

    No, you want the fronts to lock first, particularly in max braking situation - say at the track. Otherwise you chance losing the car before you can react - particularly if you are still turning (whoops) and going downhill. Truly effective front/rear brake control require separate master cylinder and a brake bia bar to vary the force applied to each.

    As I understand it, the valve can only delay/extend the time the full force take to become effective by limiting the flow of fluid to the front/rear that pushes the caliper pistons out. Once out and solid against the rotor, it doesn't matter how big the diameter the "valve" hole is, the line pressure will be the same as before. In the first instant or two, the valve could affect immediate pressure and control which end locks first.


    The only way to change the force in a hydrolic system with would be a reduction piston setup, not reasonable for a auto brake system.

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