17. The 4R100's center support (shown) is the most common culprit when it comes to transmission failure. For this reason, Wood spends a lot of time machining down this aluminum part so that a steel snap ring can be installed in front of it. The steel then becomes the wear surface instead of the aluminum. We don't expect you to visualize this unless you've seen the inside of a 4R100; just know that this simple step is one of many machining processes each Wood transmission undergoes.