Drum brakes, n:
The bane of your DIY mechanic's existence. I would rather rebuild my entire engine than rebuild my drum brakes.
Unfortunately, drum brakes are ubiquitous. Unless you have a high end car, or opted for the "4 wheel disc brake" package, you have at least one set of drum brakes in your driveway. If you have an old car rusting to death somewhere, it could have 4 wheel drum brakes. Those tricky bastards are everywhere! Let's get some intel.
This ASCII art for this would be extremely complex, so Google is your friend. Get yourself a good head on shot, not an exploded view.
Drum Brake Components
- Drums may not be in your picture. If you take the tire off to examine the drum brake, you'll be staring at a flat surface. That's the drum. With both hands, pull it straight towards you off the wheel studs to reveal the actual braking mechanism. If you examine the inside of the drum, you should find an amount of black dust and a shining silver surface.
Drums occasionally need machining, or "turning" in automotive phraseology. They must be replaced when subjected to abuse.
- Wheel cylinders should be the easiest thing to identify next. At the top of the brake apparatus you should see a cylinder oriented horizontally. The brake lines coming from the master cylinder and power booster connect to the wheel cylinders which transfer pressure from the hydraulic brake fluid outward to the brake shoes. The ends are covered with rubber caps and usually contain a spring with a separate set of caps.
Wheel cylinders will need to be replaced or rebuilt over time.
- Brake shoes are the metal arcs pressing into the wheel cylinder's rubber caps. As the pressure builds in the wheel cylinders, the brake shoes are forced outward in relation to the axle. This movement brings the shoes into contact with the inner edge of the drum producing friction, heat, dust and stoppage. You should be able to see the layer of brake material that makes up the contact surface of the shoe. This is what wears away and eventually allows a metal tab to rub the inside of the drum and tell you to go to Midas.
The shoes are one part the grease monkey will tell you is out of spec and needs to be replaced. Then you tell him that good people at e2 have you covered, and you'll do the work yourself.
- Adjuster Screw Assemblies differ from car to car. On my Ford, this between the bottom ends of the brake shoes. YMMV, but it will be pinched between the shoes. The most unique feature about it is the toothed gear. This allows brake adjustments to made when the shoes have become worn, but still usable. If the brakes are not periodically adjusted, they will take slightly longer to engage. On most modern cars with disc brakes in the front and drum brakes in the rear, a driver may think that their brakes are going out and apply excessive force to stop the car. However, the front brakes are fine but when the rear brakes suddenly engage with more force than the driver expects, results are indeterminate.
Adjuster screw assemblies should not have to be replaced.
- Strut bar. You should know this is by process of elimination. These physically vary from car to car, but it's whatever piece of metal that prevents the shoes from collapsing inward under the pull of springs.
If someone tries to sell you one of these, kick them in the face.
- Emergency brake cable connections are hiding somewhere. By definition, this is a cable that connects to the shoes allowing them to be engaged with no power from the engine. Note: the cable is behind the large plate that all the brake components mount to, so you probably can't see it in your diagram. While outside the scope of this node, your power brakes have no, um, power while the engine is off. Nothing can create the hydraulic pressure to actuate the brakes. An emergency brake, or hand brake, allows the rear brakes to be engaged by hand. Considering the number of people I see parking their cars incorrectly, the population at large has no idea how or why this works.
Emergency brake anything should not have to be replaced.
- Springs account for about half of the parts in drum brakes. And deep in the springs lies my intense hatred of drum brakes. It is a pain in the ass to take them all off and put them on again. Trust me. There isn't much to say here; springs hold things down or serve to draw parts back to their starting locations. It sounds simple until you have to put two shoes, a strut bar and three springs on at once and you realize you don't have 8 arms.
Old springs occasionally break (pun!) when you remove or install them, but they are available in brake rebuild kits.
Coming soon, a guide to changing the damn things!