Buying brake pads for your car
The fact that properly maintaining your vehicle's braking system is important is patently obvious. Whether or not the owner should tackle the job depends upon his capability and the availability of tools, parts and a safe environment in which to work.
Depending upon the vintage of the vehicle the owner may need brake shoes for drum type brakes or brake pads for disc brakes. Properly addressing the braking system is not simply a matter of installing new pads or shoes and then driving away happily. Especially with today's anti-skid braking system (ABS), the systems have become more complex. A service manual for the make and model of the vehicle must be included in the list of tools.
Prior to the addition of disc brakes in the 1960s, the majority of braking systems were hydraulically operateddrum brakes. At each wheel there was a brake drum within which was a pair of shoes which were pressed against the inside surface of the drum when braking. When the brake pedal was released the shoes were returned via heavy springs. Automatic adjusting mechanisms were added in the late 1950s but beyond that the system was the same since the old cable operated systems were replaced with hydraulics.
Assuming the vehicle in question is of a vintage with drum brakes or a combination of disc and drum brakes, there are several serious safety issues to be addressed. Because the friction material, the brake shoes, are inside the drum the brake dust generated while the shoes wear remains trapped inside the drum. Also, the heat generated by braking must migrate from inside the drum, through the drum wall and be expelled from the outside surface. These issues cause the inside of the drum to wear, often with deep grooves worn into the surface. These grooves must be machined out or they will wear out the new shoes in short order. When the wheel and drum have been removed the drum should be taken to an auto parts store. Most stores canturnthe drum for a nominal fee. There will be a maximum inside diameter of the drum, or a minimum wall thickness, frequently cast into the drum surface. If turning the drum violates one of these dimensions the drum must be discarded and replaced; the fee is no longer nominal.
Always rebuild the wheel cylinder when relining with new shoes. The time and effort to reline the brakes is not insignificant. If the shoes are worn out it is likely the wheel cylinder is approaching the end of its life. It would be better to rebuild the cylinder now rather than have to rebuild it and again replace the almost new shoes if a cylinder leaks and gets fluid on the shoes. Cylinder rebuild kits and brake shoes are readily available from most auto parts stores. On many drum brakes one shoe has more material on it than the other. This information will be in the shop manual and it is important to replace the shoes properly. One final strong suggestion would be to obtain a "brake spring plier". This will make removing and replacing the very strong return springs possible without injury and is also found at most auto parts stores.
Following the brake relining the hydraulic system must be refilled and the air bled out of it. Various types of brake fluid have been used over the years so be sure to use the correct one. Follow the procedure in the shop manual and be sure the brake pedal is firm before going for a test drive.
With earlydisc brakesthe operation can be somewhat simpler...but usually is not. The process would be to remove the wheel and carefully force the pads away from the disc, pressing the piston back into the caliper. Be careful not to damage the disc surface while prying against it. The owner then removes the pad retainer and pulls the old pad out. He then installs the new pads and replaces the retainer and is ready to go.
The truth is somewhat more complex. Pressing the pads away from the disc pressed the piston into the caliper, forcing the brake fluid back into the master cylinder. If the master cylinder has been "topped off" with fluid as the brake pads wear there will be more fluid than the reservoir can contain. The owner must be prepared to deal with the excessive fluid without permitting it to spray around the engine compartment.
The disc brake caliper lives in a tough environment. It is heated by the friction of braking, soaked by rain and snow and covered with dirt and debris. Some calipers have pistons on both sides of the disc with the caliper itself being stationary. With some designs there is a single piston which presses one pad against the disc and then pulls the non-piston side of the caliper against the disc. In this design the caliper must be free to slide on guide bolts which become rusty with age and jam the caliper. Piston seals age and crack and moisture gets on the pistons causing rust and corrosion which makes the pistons to stick. The bottom line is that at least by the second brake relining operation a caliper rebuild will likely be in order.
Early disc brake pad designs were not complex and these pads are also available from auto parts stores, as are most of the caliper components or completely rebuilt calipers. Some discs may be turned if the surface is grooved like what happens with drum brakes. Discs are more restrictive about the amount of material that can safely be removed. In many cases, however, the disc does not require machining. If the owner has been experiencing a pulsing brake pedal when stopping and the ABS has not been engaged, it is likely the disc is warped. Turning the disc is the only cure short of replacing the disc entirely.
With the introduction of ABS and Traction Control (TC) the brake job becomes more complex. The mechanical components are basically the same but the hydraulics is different and electronic sensors and a computer has been added. A shop manual is critical; work on the brake system should not be attempted without one.
Most systems are pressurized by the ABS pump and motor and that pressure must be relieved to work on the brakes. The manual should describe the procedure which on most systems is simply pump the pedal with the ignition off. Whereas the procedure for removing the worn pads is similar to the early disc brake designs, some of the ABS systems can be damaged by forcing large amounts of fluid back into the system by compressing the caliper pistons. In those cases the bleed screw must be opened when retracting the caliper pistons.
With pad replacement in process now would be a good time to change the brake fluid. What is a good idea on all brake systems is mandatory on ABS systems. Debris or water in brake fluid can wreak serious damage to an ABS system.
The aftermarket auto parts industry is relatively quick in developing replacement parts for new models. They will be available at most auto parts stores but a word of caution is in order. Some systems require precise adjustment of the caliper and brake pads which is accomplished with a series of shims or spacers. When removing the old components take careful note of what was used and be sure to follow the manual in new component installation. In some cases it may be wise to defer to the auto dealer to ensure there is no compromise in the part design.
If it is necessary to turn the disc the disc must be removed from the spindle with care. Some models have the speed sensor inside the disc, others use a speed sensor incorporated in the wheel bearing. Refer to the shop manual and proceed as instructed.
The hydraulic system bleeding is also not routine and the shop manual should guide this procedure.
Clearly a vehicle's braking system is very important. Until the introduction of ABS braking systems, the repair and maintenance of brakes was pretty basic. This is not beyond the capability of the do-it-yourself mechanic with the proper tools and manuals. Most auto parts stores today will rent special tools if required and can make recommendations for the best components as well as offer machining capability.
