Improve Classic Car Braking (and Safety) With a Disc Brake and Dual-Circuit System Conversion - Jim Smart @Hemmings

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The relationship we have with our classic cars tends to be a love/hate affair. We love the styling and the nostalgia of cool American iron from more than a half-century ago. However, suspension and braking systems are below par when you consider what’s sitting on showroom floors today. Drum brakes have their place, and obviously this arrangement is appropriate on a concours-restored show car where originality and show judging are paramount. However, if you drive your classic on a regular basis, maximizing your own safety and the safety of others depends upon getting your braking system up to date.

There was a time when you had to rummage through salvage yards to find a suitable disc brake package. These days, there’s a wealth of new disc brake kits for a wide variety of classic cars, from the Model T all the way up through the cars of the mid-20th century. Your decision should be based on what meets your personal needs and tastes. If your classic ride is a completely stock example, all you need are OEM-style front disc brakes, a dual-circuit master cylinder, new brake lines, and rear drum brakes.

Drum brakes have long been the mainstay of automotive braking systems. They perform quite well in rear axle positions yet are prone to fade when they get hot. When they get wet, friction is compromised and drum brakes can become unsafe. They also tend to lock up during hard braking.

If you have a performance-oriented model, or you’d just like a measure of braking performance beyond what the factory offered, the aftermarket may be able to assist. You may be surprised by the breadth of applications covered today, for both front and rear disc brakes.

Particularly important is the decision to convert your single-circuit hydraulic braking system to a dual system, meaning two separate circuits for the hydraulics fore and aft. American cars had single-circuit hydraulic braking systems prior to the 1967 model year, when dual braking systems became federally mandated. A dual-circuit braking system includes a two-chamber master cylinder, split between front and rear systems. The purpose of this is to maintain partial braking should there be a hydraulic system failure somewhere —a single leak should then affect only one circuit, not both as it does with a single-type system. In factory dual-circuit systems there is usually a pressure differential valve of some sort and a warning light to let you know you’ve lost either system. The pressure differential valve used on many vehicles has an internal “shuttle” valve that must be recentered once the trouble is corrected to turn the warning light out and enable proper bleeding of the system.

*The humble drum brake is little more than C-shaped shoes/linings within a rotating drum. Because the front brakes do most of the work, the rear drums are there more as a backup for the fronts*

Why opt for disc brakes? Drum brakes are prone to fading under hard use and, when wet, will often become seriously compromised. Disc brakes, on the other hand, are very effective stoppers.

They provide excellent braking force but are also more effective at dissipating heat, enabling them to endure severe use with good resistance to brake fade —the compromise in friction that occurs when the braking components become overheated. Even a front disc/rear drum system, with the split circuitry of a dual system, can offer a substantial improvement in braking performance and safety.

Most mainstream classic cars need little more than these cast-iron caliper, OEM-style disc brakes, and having them only in the front is usually a sufficient upgrade for normal driving. This is a Kelsey-Hayes four-piston front disc brake on a classic Mustang.

When you’re considering a disc brake upgrade, first determine if your car was ever available with disc brakes; if you determine it was not, investigate further to see if a system from a later version of your model offered discs. For example, a 1963 Plymouth was not offered with front disc brakes, but the parts from the right 1973 Plymouth could be adapted.

Of course, the aftermarket can simplify that process by providing whatever you might need for a disc conversion in kit form, eliminating the need to search out vintage parts from a salvage yard and the guesswork that can be involved in attempting to merge those items with your car. If you go this route, bear in mind that brake pad friction materials should be chosen based on the kind of driving you’re going to do. The daily commute or weekend getaway doesn’t call for hard friction materials designed for racing.

For a long time, six-cylinder Falcon, Comet, and Mustang owners couldn’t get front disc brakes. Only V-8 cars were available with them, and those models used five-lug wheels as opposed to the four-lug hubs found on six-cylinder models. However, given the intense demand in more recent years from six-cylinder owners, aftermarket companies answered the call with disc brake conversions for the inline-powered models. This example from SSBC-USA is a simple bolt-on kit you can install in a day.

BRAKE FRICTION MATERIALS

Some years ago, asbestos was commonly used in brake shoes and pads, but when the health risks became clear, the material was phased out. When working on a vintage car, use caution with unknown friction materials —the brake shoes on a 50-year-old car may well be old enough to contain asbestos.

These days, we have three basic types of brake friction materials: Non-asbestos organic, semi-metallic, or ceramic for high-performance driving. Non-asbestos organic compounds are the most common type of brake friction material and are made from bonded organic fibers that retain shape by a resin or glue. Organic brake linings are made from a combination of several proven plant-derived fibers. Non-asbestos linings have a small amount of metallic content in them, typically brass to dissipate heat while contributing to abrasiveness (friction) for better stopping.