BMW X3 service brakes consist of hydraulic brake calipers and rotors, 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. A vacuum assisted brake booster multiplies the braking force exerted by the driver at the brake pedal.
The parking or emergency brake uses an entirely separate braking system. A pair of mechanically operated cables attached to the parking brake handle actuate parking brake shoes inside the rear wheel drums (which are integral with the rear brake rotors). I cover procedures for parking brake cable adjustment and brake shoe replacement in separate tech articles.
You should check your brake rotors with every major service that you perform on your BMW X3. Inspect your brake rotors for cracks, scoring. Replace if you have a pulsation when braking. Brake rotors can look OK and still be worn out. If there is a ridge around the edge of the brake rotor, this is a good sign that they are worn out. Measure brake rotor thickness using a micrometer to determine if they need replacing. When measuring, measure in a few different spots and use lowest number. The minimum allowable thickness of a rotor is stamped on the edge of the rotor.
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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Most factory rotors and some aftermarket rotors will have a minimum thickness stamped on the rotor (red arrow). This will be in area of hat or hub flange. Clean rust away from rotor to uncover specs. There may also be a part number. See our tech article on disc brake specifications for all X3 model brake specifications. It's a good idea to inspect and replace your brake pads when replacing brake rotors. See our tech article on brake pad replacing. Always replace brake rotors in pairs by the axle. With the vehicle on the ground, loosen each wheel stud about 1/2 turn. This will help with removing them once the vehicle is jacked up. Lift and support axle of vehicle you are replacing brake pads on. See our tech article on jacking your vehicle. Remove wheels on axle you are replacing brake rotors on.
Pull brake pad wear sensor (red arrow) out of brake pad out of driver side 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.
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.
Rear: Working behind brake caliper. Remove two 16mm (red arrows) brake caliper bracket mounting bolts. Remove brake caliper bracket from wheel carrier and hang the caliper using a piece of metal coat hanger or rope. Do not allow caliper to hang from brake hose.
Next, using a 6mm Allen bit, remove brake rotor mounting fasteners (red arrows). Then remove brake rotor from hub. The rotor might be stuck so be prepared to give it a few taps with a mallet. If you are replacing the rear rotor make sure the parking brake is off before trying to remove the rotor.
Clean wheel hub using a wire brush. Remove all corrosion and rust from hub before installing new rotor. Install new brake rotor and tighten mounting fasteners. Then reinstall brake caliper and tighten bracket mounting bolts. Once calipers are installed and fasteners are tight, press brake pedal to pump brakes up. Once brake pedal is hard to push, install wheels and check brake operation.