1964-66 Ford Mustang 7" Power Brake Job Guide: Symptoms, Costs and the Right Parts

By Core Brake Parts Tech Team — Circleville, OH warehouse

A brake job on a 1964-66 Ford Mustang is really a hydraulic-system job: these cars left the factory with a single-reservoir master cylinder feeding all four wheels, so worn shoes or pads are usually only part of the story. If your car has (or is getting) a 7-inch power booster, the right parts depend on whether the front brakes are drums or discs, which transmission the car has, and whether it has a V8 or six-cylinder spindle.

How the Brakes Work on a 1964-66 Mustang

Most early Mustangs were built with drum brakes at all four corners. Each drum has two shoes pushed outward by a wheel cylinder, and a self-adjuster keeps the shoes close to the drum as the lining wears. The master cylinder on these cars is a single-reservoir unit: one bore and one fluid bowl supply every wheel at once through the factory three-port distribution block.

That single circuit is the most important thing to understand before you work on the car. A leak at any wheel cylinder, hose or line drains the one reservoir, and the pedal can go to the floor with no braking at any wheel. Modern cars split the system into two circuits so a single failure leaves you with half your brakes. On a classic Mustang, a brake job is the natural time to decide whether you keep the original layout or move to a dual-bowl master cylinder.

Power assist on these cars comes from a vacuum booster mounted between the firewall and master cylinder. The compact 7-inch booster is the size used for this chassis because engine-bay space is tight. Replacement master cylinders for factory power drum systems are listed with a 7/8-inch bore, while current 7-inch booster conversion kits pair the booster with a 1-inch bore dual-bowl master cylinder intended for disc/drum or four-wheel disc systems.

Front vs Rear: What Wears and in What Order

The front brakes do most of the stopping, so front shoes (or pads on disc-equipped cars) wear out first. Rear shoes typically last longer, but rear wheel cylinders on a car this old are a common source of leaks, and a leaking cylinder soaks the lining and ruins it regardless of how much material is left.

Rubber parts age even when a car sits. Flexible hoses crack and swell internally, and wheel-cylinder and caliper seals harden. On a Mustang that has been parked for years, plan on hydraulic parts even if the linings look fine.

Symptoms That the Brakes Are Due

• Low or sinking pedal. Usually a leak or a worn master cylinder seal. With a single-circuit system, treat this as urgent.
• Pull to one side. A sticking wheel cylinder or caliper, a collapsed hose, or fluid-soaked shoes on one side.
• Hard pedal with little stopping. On a power-brake car, check booster vacuum and the check valve before blaming the friction parts.
• Grinding or scraping. Lining worn to the shoe or pad backing, which damages the drum or rotor.
• Wet backing plates or fluid on the inside of the tire. A leaking wheel cylinder. Replace it and the shoes on that axle.
• Brakes drag after a stop. Can point to the booster pushrod adjustment, a master cylinder that is not returning, or deteriorated hoses acting like check valves.

The Fix and the Right Parts

Start by identifying what the car actually has. Look at the front: drums or rotors with calipers. Look at the master cylinder: one bowl or two. Check for a booster. Note the transmission, because the 7-inch power booster kits for this chassis are built for automatic cars; one maker notes its automatic kit only fits a manual-shift car if it uses an aftermarket cable-style clutch, and sells a separate kit for manual-transmission cars. Also check the engine, because six-cylinder cars use a smaller spindle and need V8-type spindles before most front disc conversions will bolt on.

For a standard drum-brake refresh:

• New brake shoes front and rear, installed in axle sets
• Wheel cylinders on any corner that leaks or has seized pistons
• Drums machined or replaced if scored or out of round
• A brake hardware kit with new return springs, hold-downs and adjusters
• New brake hoses if the originals are cracked or old
• Fresh fluid and a full bleed

For cars going to front discs with power assist, complete kits for 1964 1/2-1966 V8 automatic cars bundle four-piston calipers, 11.25-inch vented rotors, pads, a 7-inch booster, dual-reservoir master cylinder, adjustable proportioning valve, brackets, hoses, bearings and seals. They install on the V8 drum-brake spindles, and most original V8 14-inch wheels clear them. Replacement brake pads and rotors for a disc-equipped car are serviced like any other disc brake.

If you are replacing only the booster and master cylinder, hydraulic kits for this chassis include lines routed to the factory three-port distribution block and a pedal rod extension. One installer notes an adapter may be needed at the distribution block to step down to the kit's line size, so have fittings on hand before you start. See our master cylinders and brake boosters for replacement units.

What to Replace at the Same Time

• Shoes or pads in axle pairs. Never one side only.
• Wheel cylinders or calipers when the linings are contaminated. Fluid-soaked shoes cannot be cleaned.
• Hoses. Decades-old rubber is a common hidden cause of pull and drag.
• Master cylinder. If the pedal sinks, or if you are going to discs, move to a dual-bowl unit so a single leak cannot take out every wheel.
• Proportioning valve. Required when a disc/drum system replaces four-wheel drums, to keep the rear drums from locking early.
• Wheel bearings and seals. Front drums and rotors come off anyway; repack or replace them.

How Hard Is the Job and What Drives the Cost

A drum-brake refresh on one axle is a reasonable home job with basic tools, a drum spring tool and patience with the self-adjusters. Doing all four corners with new wheel cylinders and hoses is a full weekend on a car this age, largely because old fittings are often seized and lines can twist when you break them loose. Use a flare-nut wrench on every line fitting.

A booster and master cylinder swap is harder than it looks: space around the firewall is tight, and one owner reports short wrenches are a must. A full drum-to-disc power conversion is the biggest job, with spindle-mounted parts, new valving and a fresh bleed of the entire system.

Cost comes down to scope. Shoes alone on one axle are the smallest bill. Adding drums, wheel cylinders and hoses raises parts cost and labor time. Replacing the master cylinder adds a bench bleed and a full system bleed. A disc conversion with a new booster is the largest job by far, since it replaces most of the hydraulic system at once. Labor is usually the bigger variable on these cars because rusted fittings add time.

Torque the wheel lug nuts, caliper brackets and line fittings to the values in the factory service manual or the kit instructions, and bed in new friction material before relying on the brakes.

Frequently Asked Questions

Did the 1964-66 Mustang have a dual master cylinder?

No. These cars used a single-reservoir master cylinder feeding all four wheels. A dual-bowl conversion splits the system so one leak does not disable every brake.

Will a 7-inch power booster kit fit my manual-transmission Mustang?

Usually not the automatic version. Makers sell separate kits for manual-transmission cars, and one notes its automatic kit fits a manual car only when it has an aftermarket cable-style clutch.

Can I add power brakes to a four-wheel drum car?

Yes, but the booster kits built for disc/drum systems are not meant for four-wheel drums. Use a kit specified for drum brakes, or convert the front to discs at the same time.

Do I need V8 spindles to convert a six-cylinder Mustang to front discs?

For most bolt-on kits, yes. Six-cylinder cars use a smaller spindle, and the common kits install on the V8 drum-brake spindle.

Do I need a proportioning valve after a disc conversion?

Yes. Disc/drum kits for this car include an adjustable proportioning valve so the rear drums do not lock before the front discs.

What brake fluid should I use?

Use the fluid specified on the master cylinder cap or in the kit instructions, and do not mix silicone and glycol-based fluids.

Sources

1. LEED Brakes - 7-inch power brake hydraulic kit, 1964.5-66 Mustang automatic - 7-inch booster, 1-inch bore dual master, disc/drum only, manual-transmission note, distribution block adapter
2. LEED Brakes - manual brake hydraulic kit, 1964.5-66 Mustang - factory single-bowl system and three-port distribution block
3. SSBC - Kelsey-Hayes 4-piston drum-to-disc kit for 1964 1/2-66 Mustang V8 - kit contents, 11.25-inch vented rotors, 7-inch booster, V8 drum spindles
4. Mustangs Etc. - Raybestos master cylinder for 1964-66 power drum brakes - 7/8-inch bore for factory power drum systems
5. Classic Services - Mustang disc brake conversion kits - six-cylinder spindle differences, V8 14-inch wheel clearance