Hello again, Readers!
I was polishing up an article on a completely different subject - and no, not A/C! - when I was inspired to write and publish this one instead. Several customers came in asking for 'brakes' for their vehicles, but gave me the deer-in-the-headlights look when I asked the usual questions. After supplying the auto's details (year, make, model), they were lucky if they knew whether they needed them for the front or the back!
Before I continue, please make a note of this: The word "brakes" refers to the *entire* brake system of your auto. If you are only after 'brake pads' or 'brake shoes', you will need to use those specific terms. If you ask for a price on "brakes", you will likely get a quote for at least your rotors (or drums) as well. And as you will soon see, there IS a difference between 'pads' and 'shoes'!
I will now endeavor to name and explain the main brake system components.
Master Cylinder: This piece is located under the hood, on the driver's side, up against the firewall. Have you ever checked the brake fluid level on your vehicle? That tank (or 'reservoir') you checked is mounted to the top of the master cylinder. When you push the brake pedal, the master cylinder pushes the fluid through the lines and hoses, activating the brake systems at all four wheels.
NOTE: There is a LOT more to the brake hydraulics system topic,
but we will discuss that further in another edition.
Disc Brake System - Used on the front of all modern vehicles, and increasingly on the back as well.
Brake Rotor: This is shaped like a top-hat. The 'brim' is the friction-surface area, which is squeezed by the pads when you want to slow down/stop. The 'crown' (middle portion) sticks up/out further to mount the rotor onto the vehicle, then receive the wheel onto it. Rotors are sold 'per wheel'; there are 2 'per axle'.
NOTE: Some rotors are 'Rotor/Hub Assemblies', which means they
will have the wheel studs made onto them already. The rest
of them will have holes that line up with the studs that are
already on the vehicle. Just be aware!
Caliper: This is mounted at the top of the rotor, either towards the front edge or the back edge. It may remind you of a hand in a 'grabbing claw' position. It is anchored in place behind the rotor via a mounting bracket, The caliper holds 2 brake pads, 1 on each side of the rotor. The caliper has a hydraulically-moved piston on the 'inboard' side, which causes the pads to move. Calipers are also sold 'per wheel'.
NOTE: Loaded = w/ hardware & pads;
Semi-loaded/Friction-ready = w/ hardware;
Bare = caliper only
In all cases, be sure to ask if the mounting bracket comes with it!
Pads: These are the 'brake wear linings' on a Disc Brake system. They have a flat, semi-thick (maybe 1/4") metal backing plate, with a very thick (~1") form of baked-powder wearing material. The wearing material may or may not have a 'slot' (dividing groove) somewhere in the middle. (Some go vertically, others diagonally.) The pads fit inside the caliper housing. The wearing material ALWAYS faces the rotor's 'brim', sandwiching the rotor like an Oreo cookie. When the caliper piston sticks out, it forces the pads to squeeze the 'brim', which slows/stops the vehicle. Pads are sold 'per axle', 4 in a box.
NOTE: Most of the time - especially on the front axle - the 'inboard' pad
will look differently than the 'outboard' pad. If you see a set of
pads, and they seam to be two different pairs, that is probably
okay! If they seem to be a 4-of-a-kind (mostly on rear axles that
take disc brakes), then inboard/outboard does not matter.
Drum Brake System - Used on the rear of many modern vehicles, but also on the front of vehicles until about the early-to-mid 1970's.
Brake Drum: Whereas the Rotor was a top-hat, the Drum resembles more of a cake-pan. The inside wall of the pan is the friction-surface area. The shoes push out to rub against the front ("leading") and rear ("trailing") edges to help slow/stop the automobile. Unlike the disc system, you cannot see all of the major components from 'curbside'. Drums are sold 'per wheel'; there are 2 'per axle'.
NOTE: The vast majority of drums will have holes to receive the wheel
studs, as opposed to having the studs made onto them. Unless
you have a Medium-Duty truck or something similar - like the
ones that get turned into ambulances, dump trucks and such -
this won't really concern you.
Shoes: These are the 'brake wear linings' on a Drum Brake system. Again, they start with a metal backing plate, then add a baked-powder wearing material on the friction surface side. BUT, whereas pads are flat, shoes literally resemble a 'crescent moon'. The shoes both fit INSIDE the cake-pan - and yes, 'leading' and 'trailing' positions DO matter! A bunch of hardware (mostly springs) hold them in place, guide their movements and return them to their original position. As with pads, these are sold 'per axle', 4 in a box.
NOTE: The drum hardware resembles a complicated jigsaw puzzle when
assembled. Most technicians/mechanics do one side at a time,
using the other side as a reference picture. Yes, it's that confusing!
Wheel Cylinders: These tiny things are the drum system's equivalent of the caliper. There isn't a good non-automotive analogy readily available. The best I can do, is compare it to a chicken egg. Imagine a 'grade A large' egg, with the ends made out of rubber, and the middle made out of metal (steel and/or aluminum alloy). Now, stretch the middle a bit in length, until it resembles more of a tube with rounded ends. In the rubber ends, you see a metal screw/piston protruding slightly from each side. And on the top of the metal body, there are two threaded holes - one has an odd-headed screw in it. The slotted pistons are what force the shoes out against the inside walls of the drum. Sold 'per wheel', there are 2 wheel cylinders per axle.
There you have it: the primary components of automotive brake systems. We'll revisit this subject again soon, so we can go over the secondary components. By then, I hope to have a nice collection of photos of these pieces, so you can literally see what I mean. I just have to find the opportunity to take pictures of my stock parts at work! Then, I get to figure out the particulars on how Blogger wants me to add them. Sounds like an adventure to me!
Until next time, remember the Golden Rule... Not only good for people, but your auto, too!
PPM
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