It’s another weekend and thank you for joining us on AutoClinic. Here is a “crash course” on automotive brakes. I found this write-up on carparts.com by Charles Ofria and decided to cull it for our publication. It is quite instructive!
An automotive braking system is a group of mechanical, electronic and hydraulically activated components which use friction/ heat to stop a moving vehicle.
How does the braking system work?
When the brake pedal is depressed, the pressure on the brake pedal moves a piston in the master cylinder, forcing the brake fluid from the master cylinder through the brake lines and flexible hoses to the calipers and wheel cylinders.
The force applied to the brake pedal produces a proportional force on each of the pistons. The typical brake system consists of disk brakes in front and either disk or drum brakes in the rear connected by a system of tubes and hoses that link the brake at each wheel to the master cylinder. Other systems that are connected with the brake system include the parking (hand) brakes, power brake booster and the anti-lock system .
When you step on the brake pedal, you are actually pushing against a plunger in the master cylinder, which forces hydraulic oil (brake fluid) through a series of tubes and hoses to the braking unit at each wheel. Since hydraulic fluid (or any fluid for that matter) cannot be compressed, pushing fluid through a pipe is just like pushing a steel bar through a pipe.
Unlike a steel bar, however, fluid can be directed through many twists and turns on its way to its destination, arriving with the exact same motion and pressure that it started with. It is very important that the fluid is pure liquid and that there is no air bubbles in it.
Air can compress, which causes sponginess feel on the pedal and severely reduced braking efficiency. If air is suspected, then the system must be bled to remove the air.
There are “bleeder screws” at each wheel cylinder and caliper for this purpose. On a disk brake, the fluid from the master cylinder is forced into a caliper where it presses against a piston. The piston, in-turn, squeezes two brake pads against the disk (rotor), which is attached to the wheel, forcing it to slow down or stop.
This process is similar to a bicycle brake where two rubber pads rub against the wheel rim creating friction.
With drum brakes, fluid is forced into the wheel cylinder, which pushes the brake shoes out so that the friction linings are pressed against the drum that is attached to the wheel, causing the wheel to stop.
In either case, the friction surfaces of the pads on a disk brake system, or the shoes on a drum brake convert the forward motion of the vehicle into heat. Heat is what causes the friction surfaces (linings) of the pads and shoes to eventually wear out and require replacement. Let’s take a closer look at each of the components in a brake system and see where other problems can occur…
The master cylinder is located in the engine compartment on the firewall, directly in front of the driver’s seat. A typical master cylinder is actually two completely separate master cylinders in one housing, each handling two wheels. This way if one side fails, you will still be able to stop the car. The brake warning light on the dash will light if either side fails, alerting you to the problem. Master cylinders have become very reliable and rarely malfunction; however, the most common problem that they experience is an internal leak. This will cause the brake pedal to slowly sink to the floor when your foot applies steady pressure. Letting go of the pedal and immediately stepping on it again brings the pedal back to normal height.
Brake fluid is a special oil that has specific properties. It is designed to withstand cold temperatures without thickening as well as very high temperatures without boiling. (If the brake fluid should boil, it will cause you to have a spongy pedal and the car will be hard to stop.) Brake fluid must meet standards that are set by the Department of Transportation (DOT). The current standard is DOT-3, which has a boiling point of 460 F. But check your owners manual to see what your vehicle manufacturer recommends.
The brake fluid reservoir is on top of the master cylinder. Most cars today have a transparent reservoir so that you can see the level without opening the cover. The brake fluid level will drop slightly as the brake pads wear. This is a normal condition and no cause for concern. If the level drops noticeably over a short period of time or goes down to about two thirds full, have your brakes checked as soon as possible. Keep the reservoir covered except for the amount of time you need to fill it and never leave a can of brake fluid uncovered. Brake fluid must maintain a high boiling point. Exposure to air will cause the fluid to absorb moisture, which will lower that boiling point.
NEVER PUT ANYTHING BUT APPROVED BRAKE FLUID IN YOUR BRAKES. ANYTHING ELSE CAN CAUSE SUDDEN BRAKE FAILURE! Any other type of oil or other fluid will react with the brake fluid and very quickly destroy the rubber seals in the brake system causing brake failure.
This is where we pull over for this week edition of AutoClinic to be back next weekwith the automotive news and respond to your automotive questions sent in across all platforms.
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Remember whatever it is you get up to today, make sure it is a safe one!