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(Some smaller economy-car calipers are simply held together by spring-clips, and it is very easy to remove the pads and to compress the piston without difficulty.) Larger car and truck calipers are much more hefty and are bolted in place. The pads may come out with the caliper, or stay in the bracket, depending on the car. Place the caliper on top of the steering knuckle, or hang it with a piece of clothes hanger wire or any other place where its weight won't be hanging on the brake hose, and will not fall. You may need to siphon out some brake fluid from the master cylinder to accommodate the fluid being forced out (by the brake caliper piston). You should remove the cap to the brake fluid reservoir and cover it with a paper towel or rag to prevent any foreign matter getting in there. Some calipers have pistons that are made of ceramic or other sensitive materials, and merely prying them back with a screwdriver can crack them and require replacing the entire caliper. Consider using a C-clamp or piece of wood to force the piston back and allow the pads to be freed, as described below in installing new calipers. If either pad is down to the metal pins or backing, you'll need to machine (turn) or replace the rotors. This is also a good time to compare the wear pattern of the brakes on the left side of the car to the ones on the right side. If there is a vast difference, you'll need to replace the calipers or rotors. Some rotors easily slide off from the wheel lug bolts, but some are made into the wheel-hub and will require getting into the wheel bearings and grease repacking see below. Modern disc brake pads are ceramic, but older brake pads may contain asbestos, which can be harmful if inhaled in the form of "brake dust." If your brake pads contain asbestos, you can learn about how to clean and/or dispose of them here. Keep fluid and lubricants off of the brake pad material. Some cars, especially Ford Explorers/Mountaineers, have special lubricants on the caliper moving parts, and this lubricant cannot easily be obtained separately (ask for a "heat resistant grease made for brakes" from your auto shop). Try not to remove any of this where applicable. If these parts are dry and not lubricated, consider replacing the caliper, as you will probably notice other damage or signs of problems. Always resurface the rotors with a crosshatch pattern if within spec, if the rotors are too thin to resurface replace them. A fresh rotor surface is required for proper break pad bedding If they are leaking by the fittings or damaged, they'll need replacing but that is outside the scope of this article. If you are only installing brake pads, skip to the step beginning: Clean the caliper slide pins below. On most cars, the rotor is separate from the hub. Simply slide the rotor off of the lug studs. You may need to remove a set screw and/or use a rubber mallet to loosen the rotor. You may need an impact driver (hammer it while twisting counter-clockwise) to remove a set screw. If the brake rotor and hub are one piece, remove the grease cup, cotter pin, and castle nut from the axle to allow removal. (Only if necessary, unbolt the pad bracket from the steering knuckle. The bolts that hold this on tend to get frozen, so you may need to employ a hammer, breaker bar, Liquid Wrench, or a torch to loosen them.) Some auto parts stores have brake lathes or a small machine shop. Call before starting your job to verify hours; most machine shops are only open until noon on Saturday and are closed on Sunday. Rotor/hub assemblies can be turned if they are not badly worn or damaged, but consider replacing them if they are grooved. The shop should refuse to turn them if they are thin or damaged. The replacement parts may be expensive, especially if you're replacing the hub and its bearings instead of putting the old hub and bearings back on the car. Be aware that not all new rotor/hub assemblies include the bearings (although they may have new races in place, so that you can just "drop in" the new grease-packed bearings). You may have to install races and seals yourself, as well as pack them with grease. So a set of bearings may be a necessary purchase as well. When applicable, this is also a good time to repack your front wheel bearings. Refer to your service manual or lubrication guide for this procedure. You'll need some new cotter pins and wheel bearing grease for this, as well as a pair of needle-nose pliers. New rotors have a layer of oil on them to prevent rust while they're on the shelf. Clean this off with carb/fuel-injector cleaner; it works better than brake cleaner in this case. Reattach the pad bracket. If you are not replacing calipers, skip to the step beginning: Clean the caliper slide pins below. Make sure the brake fluid reservoir is securely closed, especially if you opened it earlier to allow for fluid to expand. Remove the "banjo" bolt holding the brake hose to the caliper. This is a special hollow bolt that allows fluid to flow through it; don't damage it or lose it. Make a note of its position or orientation; you will need to install it on the new caliper in the same orientation to avoid bending and damaging the hose. Make sure that the calipers are installed with the bleeder fittings/screws in the upper or top position. If you accidentally switch the left and right calipers and install them on the wrong side (easier to do than you think!), the bleeder fittings will be in a lower position, which will result in trapped air inside the caliper fluid chamber, which will make bleeding the brakes impossible to do. Remember, bleeder screws UP! When replacing the calipers it is also advisable to replace the brake hoses to the caliper. Reusing the old washers, or failure to put the new ones in the right place will cause the brakes to leak. Tighten the bolt firmly. Use a wire buffer-wheel, brush or fine grit sandpaper, if you will be reusing them and any place where the pads slide against the caliper or pad bracket with a wire brush. Apply silicone brake lubricant to all of those slide locations. Yes, some caliper pistons (such as some Nissan) do actually screw in and out. If so, there will be notches for a tool to engage the top of the piston. Pressing that kind of piston in will strip the threads and ruin the calipers and pistons. Using the large C-clamp: if this is the press-in kind of piston, take one of the old brake pads and place it in the caliper against the piston to place the C-clamp against. Usually a heavy duty 8" to 10" size (inner measurement) C-clamp will do, (lighter duty clamps will spring, bend or break). Slowly and evenly compress the piston back into the caliper. An even easier way to compress this piston is use a special (but inexpensive and readily available) Lisle Corp Brake Pad Spreader tool (Lisle part #24400 $7.95) made specifically for this it beats hauling a heavy 10" iron C-clamp around plus it's much faster to use! Note: Prior to compressing the piston back into the caliper it's recommended you open the bleeder screw to allow the brake fluid to come out of the caliper while you compress the piston. This keeps the dirty fluid from going up through the brake line and possibly damaging the Master Cylinder and the internal parts of the ABS System if your car has ABS. This also eliminates the mess that may occur from brake fluid that will be forced into the master cylinder. Watch out for drips on the side where the reservoir is located. (See Note above) Be careful, brake fluid will damage or remove the paint from your vehicle if it is not cleaned off instantly! On some brake calipers, blue Locktite needs to be applied to the bolts that hold the caliper to its mounting point.
Remove the caliper from the pad bracket if necessary. Remove the pads and inspect them for wear. Apply anti-squeal paste to the backing of the new brake pads, but do not install them yet. Inspect the brake rotors: Inspect the brake hoses. Remove brake rotors if turning or replacing them. Get the rotors resurfaced ("turned") at a machine shop or auto parts store that turns rotors. Install the new or resurfaced ("turned") rotors in reverse order of how they came off. Replace calipers if necessary. Drain the fluid from the caliper into a safe container for proper disposal. Notice that the new caliper will come with two brass washers, plus rubber grommets for the slide pins, pad retaining clips (if applicable), possibly new slide pins, and maybe that hollow bolt mentioned above. Reattach the brake hose with a new brass or copper washer installed on both sides of the hose fitting, that the hollow "banjo" bolt goes through. Clean the caliper slide pins if you haven't done so yet. Compress the caliper piston, or in some cases screw them in if necessary. Clean up any brake fluid that may come out of the reservoir at this point. Place the caliper back into the pad bracket, and bolt it in.