These early Mustangs come with a factory brake warning-light switch. The SSB kit includes a short length of hard line to splice the proportioning valve into the line between the warning-light switch and the rear brakes. Be sure to install the proportioning valve downstream of this switch. By carefully bending the original factory line, Moore was able to plug it directly into the outlet side of the SSB proportioning valve.
With all the hydraulic fittings secure and leak-free, we bled the front brakes. Moore started on the passenger side and then went back to the driver side using a pressure bleeder. If you have a friend help by doing it manually, pump the pedal gradually about four strokes to build pressure.
It's also a good idea to lightly tap the caliper with a plastic or brass hammer to help dislodge any bubbles trapped in the caliper. Even with a solid pedal, you may want to bleed the brakes again after a couple hundred miles to ensure all the air has been removed. After the fronts have been bled, bleed the air from the rear brakes starting with the right rear.
To finish the installation, Moore adjusted the wheel bearings and popped on the new SSB dust caps. Remember that these new semimetallic pads will need to wear in for at least 50 to 100 miles of easy driving before you attempt any aggressive, hard stops. This will allow the pads to burnish and will also remove the zinc plating off the friction surface.
Stainless Steel Brakes also makes a brake-pressure test kit with multiple adapters that allows you to actually measure the amount of hydraulic line pressure present in your calipers or wheel cylinders. This kit is not necessary to adjust your rear proportioning valve, but it does help with diagnostics.
Adjusting the Proportioning Valve
Turn the adjustment knob completely counterclockwise from full in and count the number of turns. Ours was just under 6 1/2 turns. Then turn the knob inward to place the valve halfway in as a starting point. Discs require more line pressure than drums to operate effectively, hence the need for a proportioning valve. This means the rear drums need less pressure. In addition, weight transfer under heavy braking moves weight to the front tires and unloads the rears. To determine the proper rear pressure, find a safe area where you can drive the car up to various speeds and then brake quickly. If the rear does not lock up before the front, adjust the prop valve clockwise to increase the line pressure to the rear brakes. Continue this procedure in small steps until the rear brakes lock up before the front. If you value the life of your tires, avoid locking the brakes for more than an instant. Locking the brakes slides the tires on the pavement and will only flat-spot your tires, which is not good unless you like riding on square tires. The optimal adjustment will be when the rear brakes lock up at the same moment the fronts do. Avoid premature rear lockup because this creates a loss of control and also increases total braking distance.
Parts List
SSB '67 Mustang disc kit
PN# A121
Price: $969.95 Summit Racing
Adjustable prop valve
PN# A0707
Price: $49.95 Summit Racing
Brake-pressure gauge kit
PN# A1704
Price: $39.95 Summit Racing