65 Mustang Dual Master Cylinder Conversion

Documentation of the switch from a single to a dual master cylinder and replacement of the rear brake lines. The old lines were missing and had been replaced by the wrong parts for a dual-exhaust vehicle. Included is a warning light and switch that warns if there is a failure of the master cylinder balance or if the emergency brake is left on.

I did this to my 65. It does not improve braking efficiency or allow less pedal effort for equivalent braking. It does provide you with some brakes should a hose, a hard line, or a wheel cylinder spring a leak.

I used a MC from a 67 Mustang. DO NOT USE A REBUILT MC. One, they will leak in a short time. Two, they come with the 1/2 " shorter 67 pushrod already inserted, so you will have to break an internal clip by pulling on the rod. I bought a "re-manufactured" master cylinder, before I read several forum posts warning to use only new cylinders unless I liked replacing them. Let me add my testimonial to the body of evidence supporting that statement. Front-cylinder-to-rear-cylinder internal leak after one month. To make matters worse, I, the meticulous one who NEVER throws away a parts receipt, couldn't find the receipt to return the MC. It is for the best as I would probably be lured into putting another "re-manufactured" master cylinder on just because it was free. I do learn slow.

I bought a NEW Bendix 67 Mustang manual drum brake MC. On the "remanufactured" MC, the pushrod was already attached, and the pushrod on a 65 Mustang is 1/2 inch longer than the 67 rod. The 67 rod was held in place by a clip and I had a hard time breaking that clip by pulling on the rod. Some people said it was easy, mine wasn't. With the new Bendix MC, the pushrod was supplied , but not inserted in the MC. So with the new MC I could just toss the supplied pushrod and insert the original pushrod from the 65 .

Proportioning valves and combination valves are for disk brake cars only. Do not use one of these. A distribution block from a dual system drum brake car is what is needed. With that distribution block, you will get a differential pressure valve that supplies a ground electrical connection if there is a failure in either system, front or rear. The differential pressure valve from a 67 or 68 drum brake car works well.

You could skip the differential pressure valve and plumb the front two lines through a tee to the rear MC port and the rear line directly to the front MC port. I used a differential pressure valve so I could wire up a brake defect warning light and alarm.
The rear line on a 65 Mustang ends at the distribution block with a 3/16 flare fitting. The distribution block used a 5/16. Check ahead of time so you don't have to wait a day to get an adapter, Don't believe the parts guy when he tells you they don't make such an adapter when what he really means is he doesn't stock one.

I put a 65 mustang, factory-dual-exhaust, rear brake line in the Frankenstang. I wanted to put it in the location the engineers intended, but this wasn't as easy as I had hoped. The car had dual exhaust, but they were not original and were not installed in the correct location. The old brake line was wired on to clear the pipes and there was no rear body bracket for a hardline. Where does the bracket go that is supposed to secure the rear of the brake line to the car body?

Look from the rear, with the driveshaft tunnel at the right, on the left section of the floor pan, where it goes up to clear the axle.
On the vertical suface, going left from the tunnel there is a 1-1/2 inch wide by 4 inch high reinforcement plate. A bolt through this plate holds the muffler hanger. Two and 3/4 inches to the left of the plate are two holes, one above the other. The upper hole is used to secure the rear seat on the other side of the pan. A brake bracket at this location would be directly across from the brake hose brass block where the hard lines are connected. Four inches to the left of the two holes is a vertical line stamped in the metal that I have been told was used by Ford to locate the bracket. When the bracket's left edge is against the vertical line the hose will attach to the body at a point left of the axle tube brass block and will clear the exhaust pipes as designed.
Make sure that brake hose is one for a factory dual exhaust. It is longer and has a bracket attached to the brass block.

It is very simple to put in a warning light that warns if there is a failure of the master cylinder balance. The same circuit can provide a warning if the emergency brake is left on by the addition of a single switch.

I received a question about the second timer in the circuit. The first timer turns the alarm buzzer on for a 2-second alarm when triggered by a negative pulse at threshold pin 6 . As a self-test, timer number two provides the trigger pulse when the ignition is first turned on. After the self-test, the alarm is triggered by a ground from either the differential pressure valve or the emergency brake switch. I uses a pre-assembled oscillator module as my buzzer. The oscillator circuit in the lower-righthand corner of the diagram was my original planned circuit to drive a small speaker.

Like most of my projects, I built the circuit on a circuit board and surface mounted the components. The switch for the emergency brake is a micro switch mounted in a clamping bracket that gives me the ability to adjust the switch point. The pressure differential valve must be bled to center the switch to the off position. This is done by opening the front or back port to allow leakage under pressure until the switch goes on. Then the port is tightened and the opposite port is opened until the switch goes off.