Power Brake Booster

With a little careful measuring and junkyard scrounging, we were able to source a Ford brake booster / master cylinder combination that will fit the tight confines of a 65-66 Mustang. The best part is how easily this fits the early car and how little it costs. It requires you to drill two holes, file two holes, and enlarge the pushrod hole by 1/8". Using rebuilt parts you could easily do this for around $100. Be aware, this will not work on manual transmission cars. The booster covers the clutch pushrod hole. Check your car before proceeding!!

The key part of the conversion is the booster. I took mine from an 87 Mustang with a 2.3-liter engine. The booster is approx. 9" in diameter and 4.25" deep. It is a single diaphragm design, but provides more than adequate assist.

The master cylinder I used is for an 87 Lincoln MkVII LSC. This cylinder has a 1.125" bore, providing more volume than the typical Granada 1" cylinder or the 15/16" late Mustang aluminum cylinder. In addition, the cylinder is aluminum. I’ve been told that it’s essentially the same part that Ford SVT supplies with their late Mustang brake upgrade kit.

Installation

Begin by looking at the back of the booster. There are four studs that protrude from the case surrounding the pushrod. One of the studs is slightly inboard. By chance, the upper two are very close to the same position as the existing upper two bolt holes in the firewall.
 
 

Using a manila folder or some other stiff cardboard over the back of the booster, cut a template of these stud locations and center pushrod hole.

Remove the export brace. Remove the old cylinder and pushrod. Save the plastic bushings.

Tape the template onto the firewall, centering the pushrod hole. Mark the two new holes that need to be drilled for the lower studs and the amount needed to enlarge the pushrod hole.

There were four bolts holding the pedal assembly to the firewall. Insert two 2" x 5/16" carriage bolts through the lower holes that originally held the old master cylinder. The flat heads won’t protrude and will not interfere with the booster.

From the inside of the car, remove the two blind nuts from the pedal assembly on the upper holes. You can do this by inserting a screwdriver and prying the nuts off. They are only swaged on and will come off easily. Then remove the two sheetmetal screws that protrude into the engine compartment.

Using a file and a drill, enlarge the upper holes, the pushrod hole, and drill the two lower holes.

Fit the new booster and bolt it down from inside the car. Install the pushrod.  the old pushrod was straight; the new one is offset.  The offset faces up.  The pushrod accepts the old pedal bushing and is reinstalled just as the original. The old brake light switch and the hairpin retaining clip are reused as well.

Install the master cylinder. Begin by looking at the actuating rod on the booster.  There is usually an adjustment on the actuating rod. Adjust the rod so that there is zero clearance between the rod and the master cylinder piston.   Caution: too little clearance will block the compensating ports on the cylinder causing the brakes to lock up. Too much clearance will cause too much pedal travel prior to brake actuation. Connect the vacuum port on the booster to a manifold vacuum source. Use vacuum line; fuel line will collapse under vacuum.

When the cylinder is in place, connect the brake lines. The front port goes to the rear brakes. Use either a stock or aftermarket proportioning valve to the rear brakes. Caution: brake lines MUST be double flared. Do not use a single flaring tool to make new lines. You risk a crack in the flare and a subsequent leak which could be disastrous.

Carefully bleed the brakes going from right rear, to left rear, to right front, to left front. Reinstall the export brace.

One last tip: My master cylinder has more than enough clearance when using an export brace. The stock brace will not clear this setup since it is lower. The stock brace may clear if using the stock 87 Mustang cylinder.