The function of the BMW Strut is to absorb the movement created by the wheel when it is riding down the road. When a strut is on your car, it indicates you have a vehicle with an independent front suspension. With all current models of BMW the presence of this suspension part is evident. As compared to the old style of suspension, the BMW struts replace the need for separate springs and shock on your vehicle. They are basically both parts in one. There are also a few of the replacement struts that are available that only have the hydraulic portion of this part and not the external spring. On your BMW the strut is attached to your vehicle with the top portion of this part fitting into the frame of which the nut at the top can generally be seen when you are looking under the hood of your car. The bottom of the part is then connected to the spindle on which the wheel is mounted to. The use of this type of independent suspension on your BMW is done to improve the handling ability by reducing the forward and backward play the wheel moves from 2% to 1% over the old style A-frame formation. To test the effectiveness of the strut that is currently on your vehicle is the same as done for cars equipped with shocks. The shaft of this part should be inspected for leaks. The car should also have a pressure applied to the corner of the side you wish to test pushing the body down. If the car moves more than one complete movement, up then back into a still position, replacement is recommended.