Mark Houlahan
Tech Editor, Mustang Monthly
February 1, 2000

Step By Step

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The Master Power Brakes power brake conversion for this ’66 289 C-code convertible included the master cylinder, vacuum booster with mounting bracket, firewall seal, vacuum hose, and vacuum fittings (not shown).
Our old manual drum brake master cylinder had served years of trouble-free life, but the braking performance was definitely lacking.
Use a tubing wrench to prevent damaging the fragile, old brake lines and to remove the line(s) from the master cylinder.
This front fitting was stubborn and had to be sweated loose with heat. You also should protect the fender, inner fender, and steering column tube from the brake fluid, as it will ruin the paint finish (notice the rag on the steering column tube).
Remove the two bolts that retain the original master cylinder to the firewall and set them aside. The master cylinder will be loose but you still have to disconnect the master cylinder from the brake pedal assembly.
Disconnecting the brake pedal from the master cylinder requires a trip under the dash. Here, Merv Rego is removing the locking pin that secures the master cylinder arm to the brake pedal. You also will have to remove the brake-light switch and pedal bushing.
Now the master cylinder comes out freely. Make sure you move quickly to avoid spilling any brake fluid on your car. Once removed, we found that our master cylinder also had a small weeping leak at the cylinder bore seal.
When adding the power brake upgrade, the two upper pedal support bolts must be removed to make way for the booster mounting bracket and bellcrank. Simply remove them with a socket and set them aside, as you will reuse them when installing the booster.
Though Rego has seen the firewall seal installed on either side of the firewall (including a ’641/2 convertible undergoing restoration there now with the seal on the passenger-compartment side of the firewall), it is of course much easier to simply slide it over the booster bellcrank arm and fit it to the outside of the firewall.
Depending upon your comfort level, you might want to remove the shock tower supports for more access. Since Rego has been working on Mustangs for more than 18 years, dropping in this booster took a matter of seconds for him. Ensure the bellcrank arm is in place and bolt the booster to the firewall.
Once again, Rego crawls under the dash and connects the new booster arm to the brake pedal and reconnects the brake-light switch.
The vacuum booster has an adjustable pushrod, but it is preset from the factory and shouldn’t need any adjustment. Slide the master cylinder in place over its mounting studs and spin the retaining nuts down barely snug to ensure the master cylinder is on straight.
Begin the reinstallation of any hard lines to the master cylinder now while the master cylinder is still loose enough to allow slight movement to align the brake line(s).
Once the brake line(s) have been threaded into the new master cylinder, you can tighten the master cylinder to the vacuum booster assembly. Once the master cylinder is tightened, you can go back and finish tightening any of the hard line(s) previously installed.
The power brake conversion kit includes this brass elbow to install into your intake manifold for a vacuum source for the brake booster, but since our 289 had a C4 transmission, we had to include the vacuum signal for the transmission modulator. Instead of buying a new “T” fitting, Rego quickly drilled and tapped the elbow to accept another fitting for the transmission vacuum line.
First, the original transmission vacuum line is installed to the new fitting Rego just installed.
The large vacuum booster hose is installed from the booster to the vacuum tree on the engine. Cut the hose to the proper length if necessary.
Rego usually prefers to bench-bleed the master cylinders before installing them, but this new-style master cylinder from Master Power Brakes has a bleeder screw incorporated into it. Standard DOT 3 fluid is used and Rego fills the master cylinder to capacity before bleeding it.
With an assistant behind the wheel, the master cylinder is carefully bled and the brakes are now ready to be tested.
The finished installation looks right at home under the hood, even though the master cylinder doesn’t have a screw-on lid as does the original version. While some purists might frown upon the new-style master cylinder, this owner is more than happy with his new brakes.
The only problem that crept up on the road test were some failed strut-rod bushings (being checked here by Rego after the first trip around the block) that caused the wheels to shudder under braking—which leads us to offer this advice: Make sure your suspension is sound and in good condition before you upgrade or change your brakes, as they work hand in hand with each other.

Adding modern conveniences to our vintage Mustangs is at an all-time high in the hobby. Every day we are seeing more and more Mustangs with three-point shoulder belts, high-back performance seats, four-wheel disc brakes, fuel injection, and more. Some of these items are added in the name of performance, while others are added for their comfort. But the most important category is—of course—safety. Upgrading your Mustang’s safety with modern braking, tires, shoulder restraints, and more should be on the top of your list for your daily-driven Mustang.

For those who want their Mustangs to look as original as possible, or at least fit in comfortably at the next Mustang show, many owners are opting for period-style additions, such as Deluxe belts with retractors, adding headrests to cars that option-ally offered them, and upgrading the brakes. While you might think that adding front manual disc brakes is a good choice (they are for the show crowd), in actuality front drum brakes with power assist can stop your Mustang better in daily use. The only time drum brakes get a bad rap is during repeated high-speed use, such as autocrossing or road racing, where disc brakes are the rule, or if they get excessively wet from standing water. Other than these two situations, power drum brakes are the better bet for street driving your vintage Mustang every day.

While spending some time recently working on the ’66 hard- top project Mustang at Classic Creations of Central Florida, owner Merv Rego brought up this same point about power drum brakes and that he too prefers them for street-driven vintage Mustangs. He also happened to have a customer’s ’66 convertible in for just such an upgrade, so we grabbed our cameras (we never leave the office without them) and captured the upgrade on film. For a standard drum brake car, all that is usually required to equip the car with power brakes is to add a vacuum booster and power brake master cylinder. Some applications also might require a brake pedal change as well. Our upgrade came from Master Power Brakes and is a complete kit as delivered for the year ordered.