Gear Box Transfer Case Servo Actuator Motor Repair Gear For: BMW X3 E83 X5 E53 X6 E71 X5 E70. Problem: Common on the 4x4 BMW Transfer Cases the gear inside wears out causing it to not function correctly. Symptoms: Clicking from the transfer case, 4x4 light, brake and ABS lights liight up. 4x4 inactive. Juddering from motor. Solution: Our new uprated gear using Carbon Fibre to ensure that the gear not wear. Attached to the transfer case is an actuator motor, within in this there is a poor quality Nylon plastic gear, turned by a metal worm gear. Over time the Nylon wears down and strips and leads to the gear not turning. This results in the symptoms noted above. BMW does not supply this part as a spare, they will provide a complete replacement motor, which will fail again because of the Nylon gear.