ALT-1 How Disc Brakes Work
It is undoubtedly the single most important system in your vehicle. As the old saying goes: If you can't stop it, don't start it! But how does your brake system really work?
The primary action in a brake system happens along the friction linings (brake pads and shoes). You push the pedal, the linings are depressed against the brake rotors (this is the disc) and/or brake drum (in the case of brake shoes).
Sounds simple, huh? Your dad, or perhaps a neighbor, somebody who has changed out a set of pads or shoes once or twice might make the mistake of telling you, "That's all there is to it!"
Oh, how wrong they are.
The friction points (pads and shoes rubbing on metal) are merely the final portion of the "System" that is engaged when you depress that brake pedal.
The mechanical operations in simple terms:
A series of springs and seals are the key components activated when you press on the pedal. These are located in the pedal assembly, the power-assist assembly (power-booster), and the master cylinder. Springs are vital in your brake system, and are the most overlooked parts as well. Ask any average mechanic about brake system springs and seals and they will probably scratch their head. The springs are in most cases hidden inside other components, master cylinders, power boosters, proportioning valves and especially inside your vehicle's anti-lock brake controls.
One key to remember about springs: the enemy of a spring is heat.
Most of these parts are located inside your engine compartment (the hottest part of your vehicle when it is in operation). So, when your pedal is feeling funny after Uncle Buck has changed out your brake pads, be prepared for something internal, like a weak spring or two, to send you on an epic journey of time and expense trying to chase it down.
This is exactly the sort of situation most repair shops try to avoid by "Recommending" the replacement of other related components, or at least warning you they could have a problem later. In other words: we can't see inside and test all those little springs and seals, but we know they've been exposed to heat and time and are perhaps weak. It may cause brake failure without any warning. A good service writer, the guy who is talking to you about all this, will protect himself and his company against future legal problems by making such recommendations.
Perhaps the most forgotten and most basic fact here is that the brakes on your vehicle are part of a system. A series of components designed to work together in order to stop a couple thousand pounds (or more!) of metal and humanity and do so safely. I cringe when I hear someonewho has changed out brake pads a time or twoclaim that there is very little to do when it comes to maintenance and repair of brake systems. I can assure you, if you hear someone make such a claim, you are in the presence of a very dangerous sort of ignorance!
Allow me to elaborate
You may already know that it is recommended to service your vehicle with regular oil and filter changes in order to keep the wearable engine parts in good shape. This extends the life of your engine, and, in the end, costs you less over the course of your ownership. Your brake system, THE most important part of your vehicle, has similar requirements.
Brake pads and shoes (called friction linings in the industry) are designed to degrade and wear down over time and use; they require periodic replacement. Unlike an oil change, it is difficult to determine just when your linings will need changing. Different drivers, driving conditions (stop and go traffic vs. interstate travel) and climate zones will cause variable wear and tear. Therefore, you should have your linings checked periodically; have the repair facility you go to for a tire rotation take a look (many will allow you to see for yourself!) before the tires go back on.
Have your brake fluid flushed and changed every year. By nature, brake fluid absorbs moisture from the atmosphere. The moisture condenses into water that mixes with your brake fluid and begins to rust the steel lines, springs and cast housings. All those little particles of rust are very abrasive; they will begin to work over the rubber seals (those little parts that actually generate your brake system's pressure) until one or more will fail. This can be highly disturbing in heavy traffic.
Avoid such deterioration by changing the fluid. It is the economical and common sense approach.
Heavy metal
Your disc(s) and drums: This is another place that gets the do-it-yourself guys in trouble.The disc/rotor or drum are the metal parts that mate to your friction linings (pads and shoes) and rub together, in other words, to create the friction which stops your vehicle. These metal parts are important, obviously. Also important, is the thickness of those metal components.
The D.O.T. (Department of Transportation) sets minimum standards for these components while the vehicle is in the design stage. The standards are important because the disc(s) or drums must be able to withstand the heat that is generated when you apply your brakes. The metal in the disc(s) or drums actually takes away the heat from your friction linings. If they should fail to do this function, your linings overheat and will fail to produce any friction at all. This would be like hitting your brakes and instead of stopping, you seem to be sliding, ice on ice, grease on a rail sort of situation; very disturbing for the peace of mind as well as dangerous, life-threatening, and in the least of cases, expensive!
A good brake shop will always measure the thickness of disc(s) and drums and then, only if there is a safe amount of thickness left, will they cut the surfaces to give your new pads and shoes a fresh surface to mate with. That shop is legally responsible if you have an accident due to miscalculation; the technician faces jail time and severe fines if he or she is at fault. They must tell you when your metal is too thin, warped or damaged and needs replacing. Cutting the surfaces too thin will cause overheating, warping of the surfaces (this is when your brakes shake the car violently as you come to a stop) and eventually the more severe condition of danger mentioned above. If the metal no longer has the required thickness, plan to replace them, it's that simple.
Understanding this much about your vehicle's brake system should help you when going to a shop or repair facility (as we call them today). Remember, don't be afraid to ask questions, and ask to be allowed to see the problem areas, so that you can make an informed decision. Listen to what your service writer is saying; what is needed, and what is recommended. Do what is needed when they show you the proof, the recommendations are up to you and your willingness to gamble. More often than not, these recommendations are to warn you of potential problems. If they should occur later, you should remember that warning, and, perhaps, return to the professional who was wise enough to suggest it.
