AMC-Ford-GM-Mopar Kelsey-Hayes Proportioning Valve Rebuild

This Kelsey-Hayes proportioning valve (sometimes also called a "rear pressure regulating valve") was allegedly removed from a 1968 Yenko Camaro. I believe that the same type of valve was also used on other GM vehicles, 1967 - 1969 Ford Galaxie and Thunderbird (car lines A and S), 1967 - 1969 full-sized Mercury and Lincoln (car lines A, D, and K), 1968 - 1970 Mopars (car lines B, J, L, R, V, and W), and the 1968 - 1970 AMC American, AMX, and Javelin. I believe the original GM part number for this valve is 3908326, the Ford part number is C7AZ-2B091-A, the Mopar part number is 2852 045, and the AMC part numbers are 319 0928 or 319 3798. The folks at the Camaro Research Group have an excellent article that describes their research into the 1967 - 1969 Camaro applications for this valve. Ford also used this valve as a later service replacement for the cylindrical C7OZ-2B091-B proportioning valve.

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

  • 11/16" socket or box wrench
  • Dental pick (or other small, pointed tool)
  • Narrow punch or thin flat-blade screwdriver
  • Needle nose pliers
  • Snap ring pliers
  • .45 caliber bore brush

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

  • U-cup seal
  • Piston seal
  • O-ring
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 valve is securely attached to the mounting bracket. The large plug on the bottom of the valve is often rusty and pitted, but it can typically be reused if you don't have a better one. A loose mounting bracket (missing on this particular valve) 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 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 1967 - 1969 GM Proportioning Valve Autopsy article. Soak the metal parts for a few hours in a container of liquid ammonia. Ammonia does a great job of removing tarnish from 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 bore is perfectly clean - any dirty residue that lingers in here can cause a leak! Finish cleaning the parts using alcohol and cotton swabs.
The steel plug can be cleaned with a wire wheel or by bead blasting. Rinse with alcohol when finished.

Install the new piston seal on the end of the piston. Note the orientation of the seal!

Lubricate the seal with clean brake fluid and install the piston in the bore of the valve body. Install the spring after installing the piston.

The next step is the only tricky part of the rebuild. Install the snap ring using the snap ring pliers and whatever tools (punch, screwdriver, etc) you have on hand to compress the spring far enough into the bore to get the ring to seat in its groove. Make sure the snap ring is fully seated before proceeding to the next step! If you can pull it out with a gentle tug from your dental pick it's not properly seated.

The rest of the way is easy! Install the washer over the top of the snap ring.

Install the u-cup seal after installing the washer. Lubricate the seal with clean brake fluid. Again, note the orientation of the seal! The flat side should be facing out.

Install the o-ring into the groove on the plug. Lubricate the seal with clean brake fluid.

Screw the plug into the body of the valve - and you're done!

​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.