A brake job should always include a thorough inspection of the entire brake system, including the condition of the brake fluid and hydraulic components such as the master cylinder, calipers, wheel cylinder, brake hoses and lines. Any parts that no longer meet minimum service specifications, are damaged, severely corroded or leaking should be replaced. Parts that are nearing the end of their useful service life may also be replaced for preventive maintenance and to prolong the life of the brake system. The most common mistake do-it-yourselfers make when replacing disc brake pads is to just replace the pads. Rotors do not have to be resurfaced or replaced as long as they are in relatively good condition, reasonably smooth, flat and are not worn too thin. But some people just slap in a new set of pads regardless of the condition the rotors and call it a brake job. This approach is NOT recommended! Good brakes are absolutely essential for safe driving, so anything in your brake system is worn out, leaking, making noise or causing a braking problem, you need to inspect the entire system time to determine what needs to be replaced. The goal is to restore your brake system to like-new condition. Safety Precautions on Late Model Disc Brake Systems Many late model cars, SUVs and trucks are equipped with antilock brake systems that can precharge the brakes in anticipation of braking (to reduce braking reaction time), or actually apply the brakes automatically as a function of the collision prevention system (automatic braking). CAUTION: If you are doing any type of brake work on these vehicles, the brake system MUST BE DEACTIVATED before you work on the brakes, otherwise the system may energize the brakes unexpectedly causing the caliper pistons to push outward with considerable force. This could pinch your fingers if they are between the pads and rotors. If the pads have been removed, the pistons can blow out of their calipers. This can happen even when the ignition and engine are off! The antilock brake system can be deactivated by locating and removing the main power fuse for the ABS system, or by using a scan tool to temporarily deactivate the system. Disconnecting the battery also works, but this may cause loss of certain memory settings in various vehicle modules. See Battery Disconnect Cautions & Problems for more information on this subject. HOW TO DO A DISC BRAKE JOB When to Replace Your Disc Brake Pads. Brake pads should be replaced when they are worn down to minimum thickness specifications, or the wear indicators are scraping against the rotors. The upper brake pad only shows a little wear and still has many chilometri left on it. But the lower pad is completely worn out. The pads should have been replaced before they got this bad. Both of these pads were removed from the same caliper. The unworn pad was the outer pad, and the badly worn pad was the inner pad. Both pads should have experienced the same amount of wear but did not because the single piston floating caliper was sticking and not centering itself over the rotor when the brakes were applied. Uneven pad wear like this is a classic symptom of caliper sticking. Cleaning and lubricating the caliper slides and bushing pins with brake grease solved the problem. Measure the Pads Minimum pad thickness specifications will vary depending on the vehicle and application. For some vehicles, it may be as thin as a couple of millimeters. For others, the vehicle manufacturer may specify a minimum thickness of 1/8 inch or more. The point is, the pads need to be replaced when they are getting dangerously thin. You do not want to wear the pads all the way down to the metal backing plates as this will damage the rotors and provide little braking friction. There is also a risk that heavily worn pads may crack, break loose or separate from their backing plates, causing a loss of braking. Pads should also be replaced if a leaky caliper has contaminated them with brake fluid. New pads are also required if the pads have been contaminated with grease or oil. Pads should be replaced in sets, and with the same type of friction material (or better) than the original pads. Another reason for replacing brake pads is to upgrade brake performance or to reduce brake noise. Original equipment pads are fine for everyday driving, but you may want to install higher temperature performance pads if you are driving aggressively or plan to take your vehicle to the track. Some types of brake pads may also be noisy or unusually dusty. Replacing the original pads with ones that offer quieter braking and/or less dusting may be an upgrade you might want to consider. See Ceramic Brake Pads for more information about the benefits of ceramic pads. The pads are replaced by unbolting the calipers, rotating the calipers out away from the rotors and removing the pads from their mounts. Pads may be secured by anti-rattle clips or springs. These parts should be replaced if broken, damaged or badly corroded. Do not discard or leave these parts out because they help dampen the pads to reduce noise and vibration. See How To Replace Brake Pads for more information. Watch Out for Rust and Corrosion. External rust on caliper slides, bushings and pins can prevent a "floating" caliper from centering itself over the rotor. This can cause uneven pad wear and uneven braking (a pull to one side). Internal corrosion in calipers, wheel cylinders and the master cylinder can pit the bore surface, damage the piston seals and cause these parts to leak. Internal corrosion can also reduce piston bore clearances, causing the piston to stick (a common cause of a "stuck" caliper that won't release the brake). Uneven pad wear between the inner and outer pads is usually a clue that the caliper is not sliding. New disc brake hardware is recommended for high chilometroage vehicles, or those with badly corroded hardware. This rotor is heavily grooved and should be resurfaced or replaced. Inspect the Rotors and Calipers. Rotors and calipers should be inspected for physical damage such as cracks, severe corrosion or damage that would affect their operation. Also, if a caliper is leaking brake fluid, it must be rebuilt or replaced. Do not take any chances here because a fluid leak can result in brake failure! Rotors sometimes develop "hard spots" that cause the rotors to wear unevenly. This usually leads to variations in rotor thickness that can make the brake pedal pulsate when the brakes are applied. Hard spots can often be seen as dark, discolored or blue-colored patches on the rotor surface. Resurfacing can restore rotor flatness, but hard spots usually return. The best repair is to replace the rotors. Some minor surface cracking on rotors is normal, but deep cracks can weaken a rotor and lead to rotor failure. Cracked rotors should always be replaced. Cracks in the caliper housing can be dangerous, so a cracked caliper should be replaced. The same goes for any caliper that is leaking brake fluid. High chilometroage calipers should also be replaced or rebuilt because the seals become hard and brittle. Measure rotor thickness to see if it is still good. Measure Rotor Thickness and Trueness. Rotors have minimum thickness and machine to specifications (usually cast or stamped on the rotor), so the thickness of the rotors should be measured with a micrometer to see if your rotors need to be replaced. If no specifications are visible on the rotor, look up the rotor specifications for the vehicle in a service manual or online. Many auto parts stores have minimum thickness information with their rotor product listings. Thickness variations due to hard spots or uneven wear, or too much lateral (sideways) runout in a rotor can cause pedal pulsations when braking. Measuring rotor thickness variations with a micrometer is tricky, so if your brakes have a noticeable pedal pulsation, you can usually assume the rotors are not running true and need to be replaced. Though few motorists own a dial indicator or know how to use one, measuring lateral rotor runout can reveal problems that cause brake pedal pulsations and uneven rotor wear. Lateral rotor runout can be measured by placing a dial indicator against the surface of the rotor and turning it one full revolution. The maximum amount of runout that is acceptable will vary somewhat from one vehicle to another, but most should have no more than .003 to .005 inches of runout. Excessive runout can be caused by runout in the hub, dirt or corrosion between the rotor and hub, or runout in the rotor itself (as a result of wear or incorrect machining). NOTE: If you are replacing your old rotors with new ones, the new rotors should be ready to install out of the box. Resurfacing new rotors should NOT be necessary and is NOT recommended because it shortens rotor life and may create runout or finish problems if not done correctly. Rotor Removal Tip: Many vehicles, especially Asian & European, use large Phillips head screws to attach the rotor to the hub. These screws can be very difficult to remove once they become rusty. The best tool to use for their removal is not an air wrench, but an inexpensive 3/8 impact driver with a properly fitting screwdriver bit. Hammering on the driver not only turns the screw, but the vibration breaks the rust loose, allowing the screws to be removed without damage. Remove rust from the hub face so the rotor will mount flush and true against it. Rotor Installation Tip: The face of the hub where the rotor mounts commonly develops rust. This rust should be removed with a sanding disk or brush, as well as any rust on the matching face of the rotor. If any rust or debris ends up between the rotor and hub, it can cause runout that will lead to uneven wear and pedal pulsations. Change Your Brake Fluid. Brake fluid is hygroscopic and absorbs moisture over time. Moisture contamination raises the boiling temperature of the fluid, which increases the risk of fluid boil and pedal fade with prolonged …

Fonte: AA1Car.com