How To – Servicing Disk Brakes & Replacing Pads

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    Servicing your cars disk brakes is a relatively easy task that only takes a few basic hand tools and a couple hours of your time. In this howto we are restoring an older vehicle that needs its front pads replaced. We will not be replacing or cutting the rotors but this is an option that you should consider.

    If you bring your vehicle in for service most brake places will cut your rotors / turn them in a lathe so the surface is flat. They will perform this task because it is company policy and it will give you the best possible service however if your brake rotors are in generally good condition and do not have deep groves you can probably get away with just replacing the pads on every other brake service and then having your rotors cut for the next job. This will extend the life of your rotors to some extent but if you find your brakes are not stopping your vehicle correctly or if you have a pulse (throbbing in the brake peddle) when you apply the brakes you will definitely need your rotors turned or replaced. Our official suggestion is that you always cut your rotors and drums when you replace your pads.


    Understanding Disk Brakes

    There are four basic parts of a disk brake system:
    The Rotor (which looks like a disk)
    The Caliper (the thing that clamps around the rotor)
    The Caliper Mounting Bracket (which the caliper is attached to)
    The brake pads (which are squished inside the caliper against the rotor disk to make the car stop).

    There are a number of parts inside the Caliper including the Piston (one two or four), the piston seal and O-ring and the rubber bushings that keep dirt and moisture out away from the mounting bolts.

    Calipers are usually attached  to the mounting bracket by a mounting bolt at the bottom and a mounting pin at the top. The mounting pin allows the caliper to slide as the brakes are applied and also has a bolt that retains it to the mounting bracket.

    In addition to holding the caliper in place the caliper mounting bracket also holds the brake pads. Four spring type clips are used to hold the pads but they do not need to be removed to remove the pads. Take careful not that the caliper bracket clips are all different and must be inserted correctly or the pad will not fit correctly. The top and bottom clips are easy to differentiate and usually of different sizes but the inside and outside clips (left right on either the top or bottom) must also be installed in the correct side or the pad will not insert correctly. If you find you are having problems inserting your new pads later then make sure the clips are in correctly and fully.

    A quick inspection port is usually present in most caliper designs. It will be located in the center of the caliper and will allow you to check the thickness of your pads.

    Inside the caliper there are one or more pistons. Multi piston designs are likely to be seen on larger vehicles or those with performance after market parts. More pistons does not mean higher safety in a catastrophic event such as seal failure. More pistons simply applies pressure to the brake pads more evenly when the pad has a larger surface area. It can also mean more braking power however higher fluid pressure would need to be delivered to the caliper. Simply changing the caliper for a multi piston design would split the pressure across the pistons.

    Each piston has an o-ring around the center of the piston which keeps the brake fluid from coming out and a seal or boot which mounts to the caliper allowing the piston to move in and out and not bring moisture or dirt into the caliper piston chamber.

    Caliper Bleed Valves are placed to allow the bleeding of air from the brake system. Normally you do not need to bleed your brakes when simply changing pads. If you are at the interval where brake fluid should be flushed from the system you would attach a vacuum pump or perform the flushing manually by opening this valve and allowing new brake fluid to enter the feed lines and caliper from the master cylinder reservoir. See our brake bleeding HowTo for more information.

    The Rotor Disk is mounted to your axel hub by four screws in a fixed position and will rotate as the axle turns.  When the caliper pistons compress the brake pads against the rotor the vehicle will stop through friction. Rotors which are worn must be turned on a brake  lathe to remove imperfections however new rotors are ready for installation after being wiped down with brake cleaner.  The cost to resurface a rotor should be $15 or less.

    Brake Pads are installed as pairs and there is an inside and outside pad on most vehicles that can be distinguished by a clip or marking that is physically attached to the pad. Brake shims are thin pieces of metal that are the same shape as the brake pad and sit between the caliper piston and the brake pad to reduce chatter or noise and squealing.  Some pads do not come with brake pad shims and may require a separate purchase however some pads have been redesigned to eliminate the shim.  It is very important that you use the shim if required.

    Getting Started

    First raise the vehicle and place it on jack stands with the remaining wheels secured by using wheel chocks to stop the car from rolling.  Once the vehicle is secure then remove the tire from the side you will be servicing. If you are working on the front brakes then turn the wheel of the car in the direction of the side you are working on to provide better access to the brakes.

    Inspect the Rotor for wear some pad designs have wear indicator tabs that will dig into the rotor when the pads need to be replaced. If you have deep groves or pulsating in your brakes when you apply them then you will want to remove the rotor after you have removed the caliper and have it serviced at a machine shop or buy a new one.

    Inspect the pads through the service port and look for any brake fluid leaks. If the area around caliper or the brake pads are wet you will probably need to replace your calipers.  Service kits with seal boots and o-rings are available for about $15 per side or less however brake calipers are also not that expensive and often come with new pads.

    Begin by removing the lower caliper bolt with a hand socket wrench. If the bolt seems tight then tap the head of the bolt with a hammer to unfreeze the threads. Caliper bolts are notorious for snapping off and will result in the need for you to buy a new caliper bracket  and bolt which can be expensive.

    Once the bolt is free you can lift the bottom of the caliper up to reveal the brake pads and the piston.

    You will note that the pads are held to the caliper bracket with 4 clips. The clips are spring loaded and do not need to be removed to remove the brake pads.

    Inspect the brake pads for wear and note the wear indicator cut that is in the center of the pad. When this cut is no longer visible then the pads must be replaced however replacing them early is not a bad idea.

    When you remove the pads look for a clip on the inside pad this will aid in your selection of pads when you install your new ones.

    Preparing New Pads

    Every time that you install new pads you need to prepare the backs of the pads and the shims with brake pad anti-squeal. Place your new pads face down on a clean piece of newspaper  and spray the backs with about 3 coats. The backs of the pads will become sticky and you need to wait for about 10 minutes before you can install them. You want to install them tacky but not wet… and before they dry.

    You also need to coat your pad shims if your vehicle uses shims.

    I like to place the new shim on the proper pad to stick it in place after the backs have had time to dry but before installing them. This will make sure the shim is properly located when installed.

    Compressing The Caliper Piston

    Here you can see what a new pad looks like next to an old pad that is being replaced. Although the wear indicator cut is still visible the new pad is twice as thick as the old one.

    When you install new pads the caliper piston will be expanded and not allow it to pass over the new thicker pads.

    You must compress the caliper piston back into its hole with a C-Clamp.

    You will also most likely need to remove about 1/3rd of your brake fluid from your master cylinder reservoir before you compress the pistons back in the chambers. I do not suggest that you keep this fluid. When you are done the job top off with new fluid. Remove the Master Cylinder Reservoir cap to reduce pressure when compressing the piston.

    First clean the rubber seal boot around the piston with brake cleaner to remove the dirt. This will allow the boot  to compress back into the hole with the piston easier.

    Using an old brake pad place it between the piston and the c-clamp and begin to tighten the clamp to compress the piston. It should move easily and slowly so do not force it. Remember fluid is being compressed back through your brake system so it will take a few seconds.

    Greasing The Caliper

    Every time that you service your brakes you should grease the caliper slide pin and inspect the boots.

    Caliper grease is a special formula that can withstand the temperatures transmitted through the brake system and resist contamination from brake dust. You should never use axle, suspension or general purpose grease on your brake systems.

    As you can see one of the brake bushing boots had some damage and it is important to replace broken boots as soon as you find them damaged.

    Boot kits come in front or back sets and will provide all the boots necessary to restore both sides of the vehicle. New calipers should also include fresh boots.

    Once greased and the boot is put in place you can install the caliper in its open position on the top caliper pin.

    Installing the New Pads

    Once your pads have dried to the tacky stage and you have made all your other repairs to boots and adding grease the final step is to install the new pads.

    You should clean your hands or gloves thoroughly before handling your brake pads.

    Also make sure that you wipe down any grease that might have got on the caliper while greasing.

    This is pretty easy to do the pads are held to the caliper mounting bracket by four clips. The clips should be installed before you press the shoe into place. If you find that the shoes will not insert easily make sure that the clips are fully seated and that the tops are in the top bottoms in the bottom and that the right and left sides are properly matched. Sometimes you can reverse the bottom clips by accident so don’t force the pads in.

    Make sure that you insert the correct shoe on each side. On this car a Tab is mounted on the inside pad and no tab on the outside tab.

    On this vehicle shims are required and have been prepared with anti-squeal spray just like the back of the pads.

    Check that the piston is still pressed flush back into the caliper and lower the caliper onto the pads.

    Once the caliper is in place you can install the lower caliper bolt mounting pin but you should first clean the threads with a brass wire brush and apply anti-seize compound to the threads so it will not get frozen in the caliper bracket.

    The caliper bolt is usually torqued hand tight to about 25-30 foot pounds but check your manual for exact specs.

    Final Note

    Performing work on your car is a great way to save money. Replacing brake pads can be done by most people if you take your time, get a good manual for your specific vehicle and follow directions.  This HowTo is a review of the process and not specific to your vehicle and may be missing information you need.  Always refer to your manufacture for exact repair guides.

    You should also compare the cost of having the work done by a mechanic. Often the cost is not so much higher that the addition of a warranty is worth having someone do the job for you. However by doing the work yourself you may allow you to purchase better parts that do not come with a standard brake service or catch other problems without an additional charge.

    See our other HowTos for information about other parts of your brake system and vehicle.

    The YouRepair Store sells a full line of automotive tools and parts. Most orders over $25 ship for free.

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