We tackled the front brakes in a previous article, and now let's take a look at rears. Some things will be the same if you have disc brakes, but many times, the rears will be drums brakes. So we'll look at those, and some other aspects of what can be different on the back of the vehicle. Older Jeeps can have drum brakes on the front, but the basics for rear drums brakes will be very similar. Rear Brake Shoes
- The shoes do the heavy work on the rear brake drum system. The force of the shoes pushing outward against the inside of the brake drum causes friction, and brakes the vehicle. Like brake pads, the materials can vary from brand to brand. Asbestos materials have been eliminated for health reasons, and a typical lining now uses a more organic or slightly metallic compound. Brake s
are sold as a set of four, two for each rear wheel. The linings can be attached to the metal backing portion of the shoe in two ways, either riveted
(using metal rivets) or bonded
(using a powerful high grade glue). There has always been a debate about which might be stronger, but with modern materials, it's hard to say for normal driving. The downside to rivets is if you drive too long on worn out shoes, the rivets will carve up and probably destroy the inside of a drum. In heavy duty and severe applications, the shoes are usually riveted. Shoes wear out just like a brake pad. Over time while driving, the material is worn off until it is gone. There is a minimum thickness, but the shoes aren't visible unless you take the drum off. So as a routine to maintenance, it's good to take a drum off and inspect them from time to time. Brake Drum
- The brake drum, made of steel, is the surface that the shoes push against to create the friction and stopping power. There really isn't much to a drum, depending on the year of the vehicle, they haven't changed much. On some vehicles, the drum can have wheel bearings and a seal, similar to the front drums on a car, or even later disc brakes. In those cases, you have to repack the bearings, and the drums have to have a good race inside for the bearing to reside in. A grease seal is usually used as well. Later drums might only slide on and off, as the hub portion is part of the rear axle. Wheel Cylinder
- The wheel cylinder carries the hydraulic pressure from the braking system to the shoes. The cylinder is normally mounted on a backing plate, usually at the top. Pressure is carried out each end of the cylinder to apply the force evenly on the two shoes at the same time. Wheel cylinder wear out over time. The insides can become worn or pitted, and the rubber cups or metal pistons will no longer operate smoothly as they should. Soon the brake fluid can bypass the cups, and you will have a leaking wheel cylinder. This results in a loss of braking control, which can be dangerous. The brake fluid will leak into the drum, and cover the shoes, thus contaminating them, and making them almost useless. Leaking wheel cylinders should be dealt with immediately, and normally both sides are changed at the same time as a measure of preventive maintenance.
Some wheel cylinders can be rebuilt. Using a brake hone to properly add a finish to the inside of the cylinder allows new rubber cups and pistons to work correctly. If the cylinder has been rebuilt and honed to many times over the years, oversized cups or pistons may be needed. Brake Hardware
- Drum brakes use a multitude of parts
to make them function. All these parts are known as hardware, and often are available as a kit that gives you all those loose parts in a box. Rear drums often have a dual purpose. While they do the braking, and that's their prime function, they can also act as part of the parking brake system. The rear brake cables connect to the hardware inside the drum, and when you apply the emergency brake, it works the hardware to make the shoes exert force against the drums. A parking brake/emergency brake is the same thing. If you park on a slope, the parking brake holds the rear wheels from turning. In an emergency, if your brakes were to fail, you can grab the emergency brake to slow and stop the vehicle. Two terms for the same thing. (The emergency brake doesn't rely on the hydraulic brake system if that fails). The hardware is made up of clips, springs, cables, levers, equalizers, and other parts. These all work together to make the brakes work. In reality, drum brakes have been around since the 1940's, so it's an old technology, but is still used today.
The hardware setup is basically the same in principle, but the exact layout can vary from one vehicle to another. If you change your hardware, it's always best to do one wheel at a time. That way, if you forget how the 15 or so parts were installed, you can go around and look on the other side to figure it out. While you don't have to replace the hardware every time you change the shoes, you should inspect them. Water and northern salt can do a lot of damage to the frail springs and other parts over time, so when in doubt, it's best to replace them. (of course, usually what happens is a spring or part will break when you take it off, so you end up replacing the hardware anyway, even if you didn't initially plan too). Major parts of hardware can be things such as the Equalizer bar
. That bar of steel connects the two shoes, usually it's located just below the wheel cylinder. It helps keep the shoes working together when applying force. At the bottom is usually the adjuster. This is how you adjust the shoes so that they are in the proper location, meaning, how far away is the shoes material from the surface of the drum. For a basic idea, it might only be 1/8" of an inch. The drum needs to be able to rotate freely. The adjuster at the bottom has a 'star' feature on it.
That's so you can adjust it from behind through the backing plate, even if the drum is installed, There's a small hole at the bottom, and a tool, what's usually referred to as a "spoon", is used to make the adjustment. Sometimes a rubber plug will cover that hole to keep moisture and debris out, but there should be a hole. When you drive in reverse, and use your brakes, that can also self adjust the brake shoes. For such an old system, all those small parts work pretty good to keep your drum brakes working. Those are the major parts to a rear brake and drum system as far as the parts. The wheel cylinders use a metal brake line, and those rarely go bad. There is usually a rubber brake hose near the differential, and that should be checked and or replaced when needed. The one hose feeds both metal brake lines that feed to the wheel cylinders. Some of the Brake Parts we carry by Brand are:
Now you know the basic parts, and you know what to inspect, and what parts you may need to order for a brake job. See ya on the trails!