When you get right down to it, the physics of braking is taking the kinetic energy of a moving vehicle and transforming it into heat energy. Okay, so what the heck does this have to do with stopping a Mustang? Plenty. When we step on our Mustang’s brake pedal, we are forcing brake fluid under pressure from the master cylinder through steel lines and hoses to hydraulic servos (wheel cylinders or calipers) that move brake pads or shoes into the rotating mass that is a brake drum or rotor. The friction material that contacts the rotating iron or steel mass slows the rotor or drum to a stop, which heats up the pad, shoe, rotor, or drum. We are transforming kinetic energy (motion) into heat energy when we apply resistance to that kinetic energy.

When we get past the theory of braking relativity, our objective is basically one thing: to stop safely and soundly. So what are brakes? What are they made of? What do they do? And how do they do it? Mustangs are equipped with two basic types of brakes: drum and disc. Some have power assist to ease braking effort.

Braking begins with a Mustang’s brake hydraulic system. Hydraulics puts fluid to work for us. Hydraulic pressure could literally move the planet. Because we cannot compress fluid, we ̴move” it through lines and hoses to the device we need to do the work. When you step on the brake pedal, the master cylinder moves fluid through the lines and hoses to the wheel cylinders or disc brake calipers, which moves the shoes or pads against the rotating drum or rotor. If there is air in the fluid, we compress (squeeze) the air and fail to move the brake fluid effectively. This is why brakes that need bleeding (getting the air out) feel spongy. When there is solid brake fluid between the master cylinder and wheel cylinder/caliper, we have a hard pedal and effective braking.

We bleed the air and contaminated fluid out of a braking system by having someone step on the brake pedal, then opening bleeders at each of the brake cylinders/calipers to remove air. Once all air and contaminated fluid are removed from the system, braking efficiency improves dramatically. Braking systems should be flushed and bled at every brake job. This keeps the fluid fresh and effective. Contaminated brake fluid hurts braking effectiveness and your safety.

Drum Brakes

Drum brakes have been around since the beginning of the 20th century and there have been many variations along the way. Most classic Mustangs (1965-’73) were equipped with drum brakes. All 1974-’93 Mustangs were fitted with front disc brakes. Mustangs after 1993 were fitted with four-wheel disc brakes. This should tell you something about braking technology. Drum brakes are old technology. Front disc brakes have been available as an option on the Mustang from day one.

A drum brake is more complex than a disc brake because there are more parts involved. The wheel cylinder receives hydraulic pressure from the master cylinder when we apply the brakes. Wheel cylinder cups and pistons move outward against the “C”-shaped shoes lined with friction material. The friction material contacts the rotating drum, which is an integral part of the axle and wheel. This friction brings the drum, wheel, and tire to a stop. Three return springs pull the shoes away from the drum when the pedal is released. A star-wheel adjuster between the two shoes at the bottom adjusts the shoes in or out.

Self-adjusting drum brakes employ even more parts. All Mustangs prior to 1994 have self-adjusting drum brakes. The self-adjuster consists of a cable, pivot hook, and return spring, and it only works when backing up and applying the brakes. As the shoes contact the drum while backing up, the pivot hook (tied to the cable, shoe, and return spring) moves away from the star-wheel adjuster, then returns, moving the star-wheel adjuster, thus moving the shoes closer to the drum. When properly maintained, self-adjusting drum brakes work quite well, but they quit working whenever the pivot hook is damaged. They also quit whenever the star-wheel adjuster ceases. A good rule of thumb is to inspect the self-adjuster for proper operation any time you repack wheel bearings or rotate tires. Get familiar with your drum brakes. They can save your life.

The parking brake holds one of the rear brake shoes against the drum to hold the vehicle. We pull on the “T” handle, press the parking brake pedal, or pull up on the handle, which pulls a cable tied to the rear drum brake shoes.

Drum brakes deserve more credit for braking effectiveness than we give them. Drum brakes offer us more braking surface area than a disc brake. They can be very effective, especially at the rear axle. The problem with drum brakes is their effectiveness in some situations. They’re downright dangerous in wet weather. If they get soaking wet in high water, for example, they will not stop a car because water between the shoe and drum causes the friction material to hydroplane, just like a tire does on wet pavement. Water keeps the friction material from contacting the drum and stopping the vehicle.

Drum brake maintenance should include a regular inspection schedule. Pull the drums and inspect them every 5,000 to 10,000 miles. Lubricate the star-wheel adjuster with a thin, high-temperature grease. Examine the wheel cylinder rubber boots for evidence of leakage. If there is brake fluid inside the rubber boot, rebuild or replace the wheel cylinder.

If your drum brakes tend to be noisy, when are they noisy? If they squeak when you’re applying brake pedal pressure at a standstill, there isn’t enough lubrication between the shoe and the brake backing plate. If they squeal during application with the vehicle in motion, the shoes and drums are glazed and should be serviced. Drums and shoes become glazed whenever there has been heavy braking and severe heat. They can also become noisy whenever the drum has been turned too many times and is out of tolerance. Then the shoes have to travel beyond their normal travel distance, contacting the drum unevenly or not at all.

Disc Brakes

There has always been a more sophisticated, upscale attitude about disc brakes. For one thing, disc brakes outperform drum brakes by a wide margin. Disc brakes don’t fade. Disc brakes are simple compared to drum brakes. Disc brakes tolerate hard braking better than drums.

To understand how a disc brake works, we have to understand the design. First, we have either floating or fixed caliper disc brakes. Then we have one-, four-, or six-piston calipers. Disc brake caliper pistons do the same thing wheel cylinder pistons do in a drum brake. They transfer fluid pressure to the friction material that stops us. The more pistons we have in a disc brake, the better. First generation Mustang disc brakes (1965-’67) have four-piston disc brake calipers. This means we have four pistons transferring pressure to brake pads on both sides of the rotor. A four-piston disc brake applies more uniform pressure to a brake rotor.

From 1968-up, Ford went to a single-piston, floating caliper disc brake that became a mainstay on Fords for many years. One large piston transfers fluid pressure to brake pads on both sides of the rotor. Because the caliper floats, pressure is applied to both sides of the rotor. Simply put, the caliper squeezes the rotor.