BMW X3 service brakes consist of hydraulic brake calipers, one at each wheel. When the brake pedal is pressed, brake fluid is forced out of the brake master cylinder and through the brake lines to each brake caliper. Pistons in the calipers push out and clamp brake pads against the brake rotors (or discs), thus slowing down the vehicle. As it ages, the brake caliper can leak fluid from the piston seal. The caliper brake fluid supply hose may also become corroded or restricted, resulting in poor brake performance.
If a brake caliper is not performing at 100%, you may notice a slight pull to one side when braking. You can service each brake caliper individually or both at the same time. Corrosion from road salt and grime may affects moving parts of the caliper other than the hydraulic piston. Sometimes you can clean the sliding mechanical parts of the caliper, including the 7 mm Allen sliding bolts (see replacement procedure below), and this results in the caliper operating smoothly again. But if this does not work, I recommend replacing the calipers in pairs to maintain an even brake feel. If one caliper is failing, the other will not be far behind.
Keep in mind that when your car was serviced before, parts may have been replaced with different size fasteners used in the replacement. The sizes of the nuts and bolts we give may be different from what you have, so be prepared with different size sockets and wrenches.
Protect your eyes, hands and body from fluids, dust and debris while working on your vehicle. If working with the electrical system, disconnect the battery before beginning. Always catch fluids in appropriate containers and properly dispose of any fluid waste. Recycle parts, packaging and fluids when possible. Never work on your vehicle if you feel the task is beyond your ability.
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Lift and support axle of vehicle you are replacing brake pads on. See our tech article on jacking up your vehicle.
Remove the wheel(s) on axle you are replacing brake caliper on.
There are two ways to reduce the amount of brake fluid loss when replacing your brake caliper. One way is to clamp the hose with a hose clamp tool to prevent fluid from leaking. This method could lead to a damaged hose if done incorrectly. I prefer to use the second method: depress the brake pedal half way and hold in place with stick or brake pedal depressing tool. This will keep fluid in the master cylinder from leaking.
Depress brake pedal half way and hold in place with stick or brake pedal depressing tool (blue arrow). This will keep fluid in the master cylinder from leaking.
Pull brake pad wear sensor (red arrow) out of left side of the brake pad. Be very careful as sensor tends to break when removed. I like to use a pair of needle nose pliers to pull sensor out. If your sensor looks complete and intact (like in the photo), you may be able to reuse it. That is, if your brake pad warning light wasn't on.
Place a drain pan under the caliper. Open the bleeder (blue arrow). Using a flathead screwdriver, slowly press brake caliper piston in. This allows brake caliper to be pulled off brake rotor easily. I like to pry between the outer brake pad and brake rotor (red arrow). This way there is less chance of damaging the caliper piston. Remember when compressing the caliper piston, it will force brake fluid out of the bleeder.
Working at brake caliper using a 14mm line wrench, loosen brake hose (red arrow). Do not remove, you will unscrew hose from caliper later. You can use a regular 14mm open end wrench, however you risk damaging the hex on the brake line.
If you want to replace the brake hose, loosen the 11mm brake line nut (red arrow) using a line wrench. Then unscrew the metal brake line from the hose. Then remove the hose from the mounting bracket and install a new one in place of it. Screw new caliper into brake hose then install pads into the caliper, caliper in mounting bracket. Tighten caliper mounting fasteners and install plugs, and anti-rattle clip. Then tighten caliper brake hose. Clip brake pad wear sensor wiring harness back onto brake hose, if equipped. Bleed brakes, see our tech article on bleeding brakes. Do NOT attempt to drive the vehicle without first properly bleeding the brake system.