The BMW 3 Series is one of the most popular line-ups offered by this Bavarian motor company. To protect the sides and back of the car from muddy conditions, many 3 Series owners install mud flaps. These rubber flaps are set in the wheel arch and catch dirt and mud as it is thrown up by the tires.
Loosen the lug bolts that fasten the wheels to the car. Raise the vehicle with a floor jack and support it on jack stands. You can install the mud flaps one corner at a time by raising and lowering the car or by removing all of the wheels. Once the car is supported, finish removing the lug nuts and then the wheels.
Hold the mud flap up against the bumper liner bolts at the rear of the wheel arch, which will be on the edge of the wheel arch lip that faces the wheel. You will be using these holes to install the mud flap and possibly drilling additional holes.
Determine how many holes you will need to drill by comparing the holes in the mud flap with the bolts in the bumper liner. Any holes in the mud flap that do not line up with the bolts on the car will need to have holes drilled in the wheel arch.
Remove the bolts that correspond with the mud flap holes and temporarily install the mudflaps by installing the bolts through the mud flaps and the bumper liner holes. Use the Sharpie to mark the holes on the mud flap that will need holes drilled.
Remove the mud flap. Drill holes with an electric drill and appropriate-sized bit into the metal of the wheel arch. The drill bit should be a little smaller than the bolts or screws that came with the mud flaps. You may need to drill a hole in the bottom of the car for the bottom corner of the mud flaps. Consult the directions that came with the flaps.
Install the mud flaps by tightening the nuts or bolts that hold them in place. Some newer BMW mud flaps use a reinforcing bracket that is installed at the same time as the mud flap. Consult the directions. Put the wheels and the lug nuts back on the car. Lower the car to the ground and tighten the lug nuts by hand.