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Changing disc brakes is a relatively easy process if you have a few good tools and the necessary instructions. It is important to understand how the brakes work in order to understand better how to work with them. There are several parts to the brake assembly including the disc, the pads (which we will be replacing), the piston and the caliper.
The disc is attached to the hub and the hub is in the middle of the wheel. The disc is held in place by lugs or bolts that protrude from the hub. The large holes in the disc fit over bolts to snuggly fit against the hub. Those lugs then keep the tire on the wheel as well. If you have ever changed a flat tire, you will remember that you had to unscrew four or five large bolts to remove the tire—those are the lugs or bolts that we are talking about.
The first thing you will want to do is raise the car and secure it in place with blocks behind the rear wheels. Safety should always come first.
Then remove the tire of the side you will be changing first to expose the disc.
The disc may not be easily removed, as it often becomes seized in place. The manufacturer has built in a method for you to remove the disc even if it is seized but first try to give it a good tap with a rubber mallet. This may loosen it sufficiently. If you still don’t have success then the disc will have some holes in it where screws fit. Insert screws in the holes and evenly turn them until the disc pops off.
The caliper is responsible for squeezing the brake pads against the rotor to stop the car. Hydraulic pressure is exerted by the calipers to ensure that enough force and friction are applied to create the pressure needed to stop the car.
You may notice during the disassembly that there is more wear on one side or the other. This is due to uneven pressure because of some part of the system not functioning properly. It is important to note and fix whatever isn’t functioning properly to avoid any further repairs.
The caliper is mounted on a floating assembly to assure that it freely slides around the pads and rotor. This keeps the pads from wearing unevenly.
There are two basic types of brake pads – those made of organic material, which create a lot of dust but are very cost effective and pads made of ceramic material, creating much less dust but are two or three times more expensive.
Some believe that the reduction of dust creates a less lick surface and therefore results in a better, quicker, smoother stop. Others prefer the organic pads because they change their pads very regularly as a part of regular maintenance and don’t feel the ceramic pads warrant the price difference.
When you are in the process of disassembling the brakes, be sure you check the other parts for undue wear and tear, cracks in the hoses, brake fluid leaks, and uneven wear indicating an additional problem. Remember that brake fluid can cause damage to the paint and other car parts so pay special attention to brake fluid leakage.
Reusing or recycling the brake fluid is recommended if the fluid is still fairly light and clean. If the brake fluid is dirty or has been exposed to the air for a period of time, new fluid should be used.
Once you have removed the tire, you will probably note that the ‘squealers’ or noise indicators are exposed. The squealers are embedded in the pad and are designed to make noise when the pad has significantly worn.
If the rotor is grooved, it will need to be machine smoothed – something done by your local auto parts store for a fairly low fee.
Next, pull the caliper up and off of the pads. This is done by removing the two bolts that hold it in place and then simply lift it off. Tie the caliper up around the car’s suspension instead of letting it hang by the hoses – possibly causing damage.
If the caliper appears dirty, it should be cleaned. Brake part lube can be used to lubricate the caliper. Using oil or other lubricant not specifically designed for use with the brakes can cause a brake down of the standard lubricants and a build up of grime and dirt.
If one pad is more than 25% thinner than the other pad, this may indicate a problem with the caliper or other brake parts. If the pad on the inside is more dramatically worn, generally the caliper is at fault and will probably need to be rebuilt. If the pad on the outside is more worn, the fault is probably with the floating mechanism on the slide. Cleaning and lubricating the slide will probably resolve this issue.
The caliper bracket should be removed next to continue the disassembly and then remove the rotor. If the rotor doesn’t slide off easily, use a rubber mallet to tap it once or twice and it should pop right off. Once the rotor comes of, take it to the local auto shop to be machined or turned. They will advise you if you need to replace the rotor instead of turning it, based on its thickness.
Generally it doesn’t take much time to turn the rotors so consider buying your pads and other parts while waiting on the rotors.
Once you return with your newly smoothed rotors, put them right back on the car. Using a torque wrench, tighten them down to the specified torque. Small and medium sized sedans will generally be around 85 ft-lbs.
Insert the new brake pads into the caliper bracket. You can purchase a small tube of gel called ‘no squeal’ to be applied to the inside of the pads to prevent the new pad squeal.
Before fitting the caliper bracket back over the pads, you will probably have to press the caliper piston back into the body of the caliper before it will fit. Use a large ‘C’ clamp to accomplish this, being careful not to tear or pinch the plastic and rubber parts.
Once the piston is back in place for the new pads, the caliper will fit back over the entire assembly. Tighten the caliper bracket according to your service manual directions for torque. Replace the tire and you are ready to roll.