By coincidence, I just removed the plastic "squirrel cage" fan from the blower motor for my 1991 420SEL (W126), last night. In the W126 case, anyway, the fan is just a press fit onto the metal shaft of the motor. There is a hole in the center of the plastic cylinder that fits over the end of the motor shaft. The technique I used was to support the plastic fan on it's outer perimeter, with the motor dangling over an open space. Then I used a hammer and a Phillips-head screwdriver (a nail set would also serve) to hit the end of the motor shaft (through the hole in the center hub of the plastic fan). I also used a couple drops of penatrating oil, but it's not clear if this really made a difference.

The key to not breaking the plastic fan is to support it on as broad an area as possible. In my case, I had an empty gallon paint can laying around, and the rim of it matched the size of the fan wheel pretty well, supporting it all around its perimeter. The motor was hanging down inside the can. You have to pound on it pretty hard, and nothing happens for a while, until it finally pops free. Other posts have talked about positioning two tables close to each other to support the fan - another variant of this would be to use a Black and Decker "workmate" portable bench, where you can adjust the size of the opening between the two halves of the work surface. Getting the fan off the motor saves about a $100, but if worse comes to worse and you break the fan in the process, you can always pay the extra money for a motor with fan assembly.

Bob Schleicher
1991 420SEL, 172,000 miles