Most Mercedes blower motors are manufactured by Behr and feature plastic squirrel cage blowers. The there are a few metal cages that I have come across for older applications. The plastic cages are pressed onto the shaft of the motor. When the motor goes bad it is best to just replace the entire blower motor assembly as the cages are very difficult to remove without damaging the plastic spokes. Pressing the cages on at the right angle is also hard to achieve. Anytime the blower wheel is changed it needs to be balanced just like wheels need to be balanced when you get a new tire. Unbalanced blower wheels will cause vibration and noise. Vibration can be severe enough the make the blower cage touch the blower housing braking the blower wheel. When handling blowers assemblies make sure you do not handle the blower by the blower wheels as this can exert enough pressure to blower wheel to cause the cage to warp and vibrate. I have seen this many times in the Behr warehouse checking returns. EuroPartsAmerica.com offers aggressive pricing on Behr products that is typically lower than most online stores.
