1971 - 1974 Pantera Brake Pressure Control Valve Rebuild

This Bonaldi brake pressure control valve (sometimes referred to as a "proportioning" valve) was removed from a 1974 de Tomaso Pantera. The original Ford part number is D26Y-2B091-A. Unlike the valves used on many other cars, this valve is used to reduce brake fluid pressure to the front brake calipers.

The valve is similar, but not identical to, an earlier D16Y-2B091-A valve used  during the 1971 and 1972 model years. I'll note the significant differences below. You can click on the pictures to see larger versions of the images.

This document describes how to rebuild the valve using a new seal kit available from Muscle Car Research LLC.  Tools needed:

  • 36mm socket and ratcheting wrench
    or large open end wrench
  • Fresh, clean brake fluid
  • Dremel rotary tool with wire brush attachments
  • Easy-Off Heavy Duty oven cleaner
  • Brake cleaner
  • Bottle brushes

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

  • Copper sealing washer
  • Large rubber seal
  • Small rubber 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. If any of the port threads are stripped or damaged you're better off finding another valve. 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 1971 - 1974 Pantera Brake Pressure Control Valve Autopsy article. This particular valve was cleaned using Easy-Off Heavy Duty oven cleaner, but if you have rust to remove you'll need to remove it. Bead blasting works great; chelation is another option. No matter how you remove the rust it's a good idea to keep blasting media or cleaning fluids out of the valve body.

Clean the parts, flush with soap and water, and polish with the dremel tool. Clean the insides of the valve with brake cleaner (use the bore brush to clean the rod bore) and make sure that the sealing surfaces are perfectly clean - any dirty residue that lingers in here can cause a leak!

Start by reassembling the spool valve. First, the large rubber seal must be installed on the piston. I've received reports of people finding this seal under the ridge that can be seen just to the right of middle in the picture below, but that location seems wrong. If the seal is installed there it won't move in conjunction with the piston. Lubricate the seal with clean brake fluid and slide it onto the piston from the small end. Stretch it over the ridge so that it fits in the gap between the ridge and the head of the piston.

The remaining valve parts are installed in the order shown below. Slide the large metal disk onto the piston with the large open end facing the large seal. The ridge on the outside edge of the disk will be close to the spring when it's properly installed. Install the spring so that it fits into the recessed area in the bottom of the disk. Lubricate the small seal with clean brake fluid, install it into the seal retainer, and slide the assembly onto the piston with the seal facing away from the large seal.

Here's the completed spool valve assembly. Note the orientation of the parts. The earlier D16Y-2B091-A valve uses a longer spring that can make it challenging or impossible to install the small seal such that it stays on the piston. You'll need to install the seal when you install the spool valve in the valve body.

The completed spool valve can now be installed in the valve body. Give the valve body another look to make sure it's perfectly clean. If there is any rust or dirt in here it needs to be removed. Give the bore a light coat of clean brake fluid.

Slide the spool valve into the valve body, small end first. Make sure the end of the piston fits into the opening at the bottom of the valve.

If you're rebuilding a D16Y-2B091-A valve you'll first need to place the small seal and seal retainer in the bottom of the valve. Make sure the exposed end of the seal is facing the bottom of the body! Next, position the spool valve in the body and line up the piston with the hole in the seal.

Insert the steel ring into the end of the valve body and make sure it's seated around the top edge of the piston. Install the copper sealing washer on the large hex nut.

Please the valve in your vice and install the nut. It should be installed just tight enough the make a positive seal with the washer.

With a D16Y-2B091-A valve you'll need to compress the spring and push the piston through the small seal and the hole in the bottom of the body. It's not easy, so be patient.

Install the plug into the valve body and tighten it just enough to make a positive seal. Install the rubber dust cap to finish the job. Install the rubber cap on the other end of the valve to protect the exposed end of the piston.

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 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.