Drum Brake and Shoes Overhaul
The difference in stopping power with a newly-overhauled drum brake system is very noticeable, making your old car safer and more enjoyable to drive. Drum brake restoration requires several speciality tools and an evening or two in the garage.
Drum brake systems are divided into two categories, friction and hydraulic. This article covers the friction parts, which include the brake drums, shoes, hold-down hardware, and parking brake cables.
Brake drums are the most expensive part of the overhaul. Since warped or grooved drums effect brake performance, have yours measured to see if they can be resurfaced. Better auto parts stores still provide this service.
There are several types of brake drum construction. The most common is the one-piece cast iron style. Composite drums use a either a sheet-steel hub with an iron rim cast to it, or a sheet-steel drum with a cast iron surface inside it. Composite-style drums are lighter than cast-iron drums.
Aluminum naturally transfers heat better than cast iron, and is also lighter in weight. Many aluminum brake drums are actually bimetallic, manufactured from aluminum and cast iron. The Al-fin brake drum, once the hot set-up, used a special process for casting the aluminum around the iron.
Many sixties performance cars (Corvette's, GTO's, etc.) offered optional aluminum drums for lighter weight. Finned drums also dissipate heat (and look cool).
The larger the brake drum, the better it can dissipate heat. Larger drums also reduce brake-pedal effort. Back in the day, early racers and hot-rodders fit as big a drum brake as could fit inside the wheel.
Removing Brake Drums
Before you start banging on the back of your drum with a hammer, some drums require special tools to remove them. Having a service manual for your year and model is always a good idea. Also, remember to disengage the parking brake while inspecting rear drums, as this will prevent the drum from coming off.
Replacing Brake Drums
Sometimes, drums can be machined. Other times, if your shoes have worn as far as the rivets, the drums may be scored or too thin to be machined. Depending on your year and model, replacement brake drums may be hard to find. Many drums may be available only as used, which may not be in any better shape than the ones you're replacing.
Brake shoe friction material varies. There are organic and several qualities of metallic linings. Friction material, or brake lining, is either bonded (glued) or riveted on the brake shoe. Many performance cars of the sixties offered sintered metallic brake linings for better stopping power.
The primary shoe (the one in front) is the shorter one. Do only one wheel at a time so if you forget how it came apart, you can use the other side as a guide to put all the pieces back together. Never work on just one brake - you'll get a sharp pull or worse.
When buying replacement shoes (usually sold as exchange), make sure all the holes in the new shoes line up with the old ones. If a return spring is placed in an improper hole, dragging or grabbing brakes will result. Keep in mind that shoes may have extra holes to fit applications other than yours.
Before installing the new shoes, consider cleaning and painting the backing plates. A spray can of black engine enamel would work fine. Remember to apply a small amount of all-purpose grease to the friction points on the backing plates to help the shoes move freely.
Work on one side of the car at a time, using the other side as a reference. Before re-installing brakes, clean and spray the backing plates with black engine enamel. Apply a small amount of all-purpose grease to the friction points on the backing plates to help the shoes move freely.
The parking brake is applied by a mechanical linkage, usually a cable or cables. The rubbing points on these should be lubricated as well.
Some restorers like to 'bed in' new brake shoes. This is done by a series of short, hard stops from about 30 mph, letting the brakes cool down (about 15 minutes), and then repeat the process once more.
Many old-school drag cars still run four-wheel drums because they're lighter than discs. They also have less drag - they back the adjusters all the way off for minimum rolling resistance. This is not recommended for street-driven cars!
Most older brake shoes were made with asbestos, whose debris is dangerous to your health. Wear a dust mask when removing old drums and shoes. Don't use compressed air to clean off brakes. Use brake parts cleaner and a wire brush.
With new parts and quality shoes, drum brakes work better than most people believe. The difference in stopping power with a newly-overhauled brake system is very noticeable, making your old car safer and more enjoyable to drive. Drum brake overhauling requires several speciality tools and an evening or two in the garage.