1967 - 1969 GM 3905525 Metering Valve Rebuild

This Bendix metering valve was removed from a 1969 Chevrolet Chevelle. According to my parts catalogs the original applications include all 1967 - 1969 Chevrolet vehicles and 1967 - 1969 GM A-bodies equipped with front disk and rear drum brakes. The original GM part number for this valve is 3905525.

You can click on the pictures below 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:

  • 1 5/16" socket or large open end wrench
  • Fresh, clean brake fluid
  • Dremel rotary tool with wire brush attachments
  • Dental pic
  • .45 caliber bore brush

 

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

  • U-cup seal
  • Rubber sealing washer
  • 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. 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 1967 - 1969 GM 3905525 Metering Valve Autopsy article. This particular valve was bead blasted by a previous owner, but if you have rust to remove you'll need to remove it. Bead blasting works great, but chelation is another option. No matter how you remove the rust it's a good idea to keep blasting media or chelation 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 (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!

Now you can start to reassemble the spool valve. The order of assembly is wave washer, small spring, spacer, large spring, and steel washer.

Here's the completed spool valve assembly.

Install the rubber sealing washer into the cup end of the spool valve. Make sure that the edges are fully seated below the cut-outs along the edge of the cup. It helps to give the washer a light coat of clean brake fluid.

Now turn your attention to the valve body and the u-cup seal. The flat part of the seal is the bottom. Coat the seal with clean brake fluid.

Insert the seal into the opening at the bottom of the valve body. Press it into place with your dental pick. Make sure that the lips of the seal are facing towards you!

Hold the valve body up so that the large opening is facing towards the ground. Insert the spool valve into the valve body by pushing it up into the body so that the rod goes through the u-cup seal. If you push the spool valve up into the body you won't have to worry about the parts falling off, which can happen if you try to push the spool valve down into the body on your work bench.

Now find the o-ring and valve body plug.

Install the o-ring onto the plug. Coat it with fresh brake fluid and make sure that it's fully seated.

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.

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.