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.
The brake pad wear warning system consists of electrical contacts installed in small cutouts in the left front and right rear brake pads. When brake pads wear down to the point that the tip of the contact touches the metal of the brake rotor, a warning light is illuminated on the dashboard. This usually happens when the brake pads are 2 to 3 mm thick (about 1/8 in). Usually, by the time the brake pad warning light illuminates, the driver becomes aware of the problem, and time is found for brake pad replacement, friction from the brake rotor has worn the top of the wear sensor down so that a new sensor is necessary. In order to avoid the expense of purchasing new brake pad wear sensors, check your brake pads every time you service your BMW X3 and replace them as soon as they reach 3 mm thickness. As the wear sensor is only located on one brake pad per axle, 3 brake pads on each axle are not monitored by the warning system. This is why periodic inspections are necessary.
When replacing your brake pads, always replace both sides of the axle at a time and have a new brake pad wear sensor handy. Even though the sensor may be reused, they become brittle and do not always fit tightly into new pads when reused.
In this article, I will show you how to replace brake pads on the front axle of your vehicle. Replacing the rear brake pads is similar.
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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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 pads on.
Using a flathead screwdriver, remove brake caliper anti-rattle spring (red arrow) by prying out while securing with hand. The spring can pop off and go flying, be sure to hold it steady.
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.
Press piston back into caliper using a brake caliper piston tool or a C-clamp. Open the bleeder screw (red arrow) and catch the escaping brake fluid in a suitable container when compressing the piston.
Clean the brake caliper and the brake caliper mounting bracket (red arrows). Install new brake pads into caliper and caliper mounting bracket. Install caliper to mounting bracket and tighten fasteners. Then install rubber plugs.
Working behind front strut, open plastic door (blue arrows) for brake pad wear sensor electrical connector. Disconnect brake pad wear sensor electrical connector by pressing release tab (red arrow) and pulling it straight apart. Connect new pad wear sensor electrical connector and route wiring harness as before. Install brake pad wear sensor into brake pad. Install brake pad anti-rattle clip by pressing into caliper and pushing down to confirm it is properly seated. 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. Bleed brakes if necessary.
Servicing the rear is similar, except for accessing the right rear pad wear sensor. To access the rear sensor, locate the sensor connector housing splash shield, located just in front of the rear wheel near the trailing arm. Remove the plastic rivet (blue arrows) using a trim panel tool. Then, remove the two 8mm fasteners (red arrows).