1993 - 1996 GM 10223533 Combination Valve Rebuild

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This document describes how to rebuild the 1993 - 1996 GM 10223533 (ACDelco part number 172-2104) combination brake valve using a new seal kit available from Muscle Car Research LLC.  Tools needed:

  • 19mm socket or box wrench
  • 5/8" deep socket or box wrench
  • Dental pick
  • Long thin punch (or other tool to push with)
  • Ball peen hammer
  • Clean brake fluid
  • Pine-Sol® cleaner
  • Fine steel wool
  • Thin brass bore brushes
  • Spray brake cleaner
  • Cotton swabs
  • Semi-gloss black paint
  • Bead blaster (optional)

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

  • O-ring seals
  • Piston seal
  • Retaining 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 body is securely attached to the mounting bracket. A loose mounting bracket can be tightened up by lightly tapping the mounting tab with a ball peen hammer. 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 1993 - 1996 GM 10223533 Combination Valve Autopsy article. Soak the metal parts for a few hours in a container of Pine-Sol® cleaner. Remove the parts, flush with water, and polish with steel wool. If your valve is expecially cruddy, it may help to bead blast the exterior surfaces. 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 brake cleaner and cotton swabs.
 
Rust can be removed from the mounting bracket with a wire wheel, bead blasting, or chelation. Spray the bracket with semi-gloss black paint as needed. Lay out the clean parts and your rebuild kit.

Let's start with the proportioning valve assembly. The nut at this end of the valve uses two o-ring seals.

Lubricate the o-rings with brake fluid. Install the smaller o-ring into the top of the nut. The larger o-ring fits into a groove just under the head of the nut.

Next, install the piston seal into the groove on the end of the piston. The "open" end of the seal should be facing outward when the piston is installed. In the picture below, the open end of the seal is to the left and the flat end of the seal is to the right.

Install the piston into the bore of the valve body.

​Install the spring.

Install the metal cup with the flat end facing you. The raised edges on the inside diameter should fit into the end of the spring.

Install the completed nut assembly just tight enough to keep it from coming loose and add the rubber cap (Sorry, the seal kit doesn't include a new rubber cap. If you need one you can scavenge one from another used valve found on a large number of GM vehicles from the same time period). The proportioning valve rebuild is complete!

Now let's turn our attention to the pressure differential valve. This assembly includes another sealing nut, a piston, a brass spacer, multiple o-rings, and a retaining ring.

Start by installing the large o-ring on the nut. Lubricate it with clean brake fluid and roll it into place with your dental pick.

Install the remaining three o-rings on the piston. Note the orientation of the o-rings and the spacer! DO NOT install the o-ring in the groove under the spacer! Press the retaining ring into place with the raised side of the "fingers" facing out towards the end of the piston.

Here's a closer view of the retaining ring. Note that it's slightly dished. The raised edge of the ring should be facing outwards toward the end of the piston.

The trickiest part of the reassembly process is in inserting the piston. It's a tight fit, and you have to push it in just far enough for the deep groove to be centered beneath the port used for the sensor switch. A thin punch works well. Apply gentle pressure and watch your progress by looking through the switch port hole as you push. Stop pushing when the groove is visible. If you push too far you'll have two choices: disassemble the valve and try again, or complete the reassembly and try to re-center the piston after the valve is reinstalled on the car. This can usually be done by quickly applying a lot of force on the brake pedal.

Install the nut and o-ring. Again, it should be just tight enough to keep it from coming loose.

Install the sensor switch and the valve assembly is complete!

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. 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.

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