Mustang Disc Brake Proportioning Valve

STEP 5: Carefully open up the crimp clip, until you can slip it off the inner piston. This clip is soft metal and is meant to be reapplied by crimping it back with pliers. You must reuse this part so don't flex it any more than needed or it may break. Now, remove the small seal and slide off the spacer collar. The inner piston should now slide out of the outer piston. Remove the old large seal from the outer piston.

NOTE: On the end of the inner piston is a thin rubber washer called the bumper pad. It is easy to recognise due to its serated edges. You must reuse this piece, it does not come in the seal kit. Handle carefully and save.

STEP 6: Clean all parts. There will usually be some rust inside the valve on the housing and the parts. Remove with ScotchBrite or fine emery paper. There are two surfaces inside the housing where the large and small seals go against. Polish these surfaces smooth or lightly hone with a brake cylinder hone. The inner and outer pistons will usually have a residue on them that will need to be cleaned off. Be careful not to gouge or scratch the surfaces. The pistons are light aluminum and can damage easily.

NOTE: The inner piston is anodized a golden color and the outer piston is a dark purple. Usually there will be some lighter patches on the purple outer piston where the anodizing has worn off. This is normal. Just clean off the brownish residue and wash clean.

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STEP 1: Install the bumper pad on the end of the inner piston as shown. Install the large seal on the lip of the outer piston making sure the lip of the seal faces the correct way (See photo).

STEP 2: Install the large seal on the lip of the outer piston making sure the lip of the seal faces the correct way (See photo).

STEP 4: Slide the spacer collar onto the assembly making sure that the side with the cutouts faces the large seal on the outer piston.

STEP 5: Install the crimp clamp by placing it in the grrove behind the spacer collar and squeezing it shut with a pair of pliers.

STEP 6: Install the small seal onto the inner piston. On the Style "A" piston, carefully stretch the seal over the end and set it in the groove. On the Style "B" piston, unscrew the special bolt, remove the washer and slide the seal on, then replace the washer and bolt. In either case, make sure the lip of the small seal faces toward the large seal and spacer collar (See photo).

STEP 7: Lubricate the inside smooth surfaces of the valve housing with clean brake fluid. Also apply fluid to small and large seals. Carefully slide piston assembly into housing.

STEP 9: Set end cap into housing on top of the piston assembly. Push end cap down until the groove on the inside of the housing for the retaining clip is visable and install clip.

STEP 10: Turn the housing over. Set the pressure spring inside; over the end of the inner piston on the Style "A" valve, over the end of the special bolt head on the Style "B" valve. Set open end of the adjuster sleeve over the pressure spring and thread into the housing. Thread in until the amount of the adjuster sleeve sticking out matches the measurement you made before you took the valve apart. Once adjusted, thread on adjuster lock nut and tighten.

STEP 11: Take the wide square O-Ring in the kit and slip over the housing into the exterior groove. This groove has a vent hole in it and the square rubber ring acts as a seal against dirt and water while venting the valve to the atmosphere.

Rebuilt valve is now ready to install. Mount to rear fender apron using the bolt hole on the side with a bolt run through the fenderwell.

Unit can be adjusted by loosening adjuster lock nut and screwing adjuster sleeve in or out to desired effect. Be sure to tighten down adjuster lock nut each time. Threading the sleeve outwards will increase the pressure going to the calipers on the front wheels, threading in will decrease it.

The valve above was painted with a cast iron type paint to give it a original natural finish that wouldn't rust. I believe these valves were left as bare cast iron as installed on the car.

To the right is a picture of an NOS valve right out of a Ford parts box. This may represent the finish of a Ford replacement valve. It is painted in a light blue with the observed paint splotch on the side.