1987 - 1993 Ford Mustang Brake Pressure Control Valve Rebuild

This document describes how to rebuild the 1987 - 1993 Ford Mustang brake pressure control valve using a new seal kit available from Muscle Car Research LLC.  Tools needed:

  • 1/2" socket or box wrench
  • 3/4" socket or box wrench
  • Liquid ammonia
  • Dental pick
  • Clean brake fluid
  • .45 caliber bore brush
  • Ball peen hammer
  • Rubbing alcohol

The rebuild kit provided by Muscle Car Research LLC includes the following parts:

  • Piston o-ring seals
  • Plug o-ring seals
  • Piston seal
Arrange your valve, tools, and rebuild kit on a clean work surface. Let's get started! The first step is to inspect the valve and make sure that the exterior is undamaged. Check the port threads for damage. Make sure the body is securely attached to the mounting bracket. A loose mounting bracket can be tightened up by lightly tapping the brass mounting tab with a ball peen hammer. If any of the brass port threads are stripped or damaged you're better off finding another tee. If your valve passes the exterior inspection you're ready to disassemble it and inspect the internal parts.
Disassemble the valve as described in our 1987 - 1993 Ford Mustang Brake Pressure Control Valve Autopsy article. Soak the metal parts for a few hours in a container of liquid ammonia. Ammonia does a great job of softening tarnish on brass, but be careful of the smell! Remove the parts, flush with water, and polish with steel wool. Clean the bores of the valve with the bore brush and make sure that the bores are perfectly clean - any dirty residue that lingers in here can cause a leak! Finish cleaning the parts using alcohol and cotton swabs.
The bracket can be cleaned with a wire wheel or by bead blasting. Rinse with alcohol when finished. Lay out the clean parts and your rebuild kit. It helps to line up the new seals with the old seals to compare sizes.

Install the new o-ring seals on the small plug and brass piston. It helps to lubricate the seals with clean brake fluid. The o-ring used on the small plug is similar in size to the smaller o-ring used on the large plug. The difference is in the thickness of the small plug o-ring - it's thinner in cross section.

Install the piston, spring, and plug. The plug should be tightened only enough to get a good seal between the o-ring and the valve body. Now turn your attention to the proportioning valve components.

Install the o-rings seals on the plug and the piston seal on the piston. Make sure that the open end of the piston seal is facing out. Lubricate the seals with clean brake fluid.

Push the piston into the valve and install the spring behind it.

Install the plug. You'll need to compress the spring while turning the plug to engage the threads. Again, don't over-tighten the plug. The rebuild is finished once you've installed the plug.

​Now you can reinstall the valve in the car and reconnect the brake lines to the valve. Start each line by hand as best you can to ensure that the fittings are threading in straight and smooth. Be careful - it's easy to cross-thread the fittings and damage the soft brass threads. Tighten each fitting with a flare nut wrench. You may need to tighten, loosen, and retighten each fitting multiple times to obtain a leak-free seal. Add brake fluid, bleed the brakes, and check for leaks.

The bracket used on this tee was originally plated with a zinc dichromate or yellow cadmium finish. If you're rebuilding the tee for use on a concours show car you will want to either remove the bracket from the tee by carefully reforming the staked brass tab that holds the bracket in place or you can send the entire valve off to have the whole assembly replated. If removed, the bracket can be reinstalled by restaking the brass tab with a ball peen hammer. If not removed, be sure to plug the ports with inverted flare plugs to keep plating material from getting into the valve. Plating material that gets on the valve body can be removed with a bead blaster or a wire wheel, but be sure to protect the bracket with masking tape.