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108 FAQ - Quick hack to replace the blower motor

I recently found a short cut to replacing the heater fan in my 108 chassis 250S. Having done that job once on the 300SEL was enough for me! I first removed the cowl sheetmetal, held in place by the windshield wiper arm shafts and some sheet metal screws. Then I cut out an opening in the sheet metal over the fan (outside, ahead of the windshield) and pulled out the badly roached fan motor from there by breaking the three motor supports arms to the motor housing with some strong pliers. Getting the nylon sqirrel cage out required a few cuts with a hot soldering iron (nasty fumes!). Looking through the blower collection at the local wrecking yard, I found one from a '76 Ford Courier pickup truck which fit into the old housing perfectly. Three long #10 screws attach the flange of the Ford blower, bent at a right angle, to the "chimney" around the blower opening. The nylon fan has to be put onto the motor shaft 'backwards' for the correct air flow; it is held on with a c-clip and goes on from the other direction just as easily. I then connected the up the wires from the original motor. The fit is excellent and blows air about as well as the original blower. I covered the hole I made with some galvanized sheet metal and sheet metal screws and some sealant before putting the outer cowl piece back on. No tell-tale signs. It took me a couple of hours to do the job, but the next time it will take about an hour. It's a "stroll in the park" compared to what MB would have you do.

The reason you can't replace it with an original motor/fan is that you would have to destroy the plastic housing and make a much larger opening to get it out and back in that way. This way you leave to outer housing of the motor in place, the Courier fan just fits inside of it. Cut the sheet metal at the cowl just big enough to slide the nylon fan and motor through seperately and assemble them then, making sure the nylon fan is mounted 'backwards'. It is easier to do than it sounds.

To answer several questions raised by my earlier posting on replacement of the 108 heater blower through the cowl area:

1. By removable cowl sheetmetal I mean the airscoop.

2. The cut out hole is approximately 3.5" by 8", speaking from memory. The position is right above the circular opening to the existing blower, which you will be able to see from an angle once the air scoop is removed. It is obvious. The hole needs to be big enough to allow the replacement motor and fan to fit through (seperately).

3. The outer frame of the original blower motor stays in place, the motor mechanism itself is removed by breaking the three supporting braces which hold and center it in the frame. It then pulls right out after disconnecting (cutting) the two wires to it which will then be attached to the replacement motor. I used crimp barrels. The original nylon blower will not fit through the motor frame, so it has to be cut in a few strategic places. I used a soldering iron to do this, but I imagine that a dremel tool or various cutters could be used as well.

4. Before closing it all up again, be sure to clean, replace or install (if missing) the screens to the air inlet. I think that leaves and pine needles jamming the blower is a common source of failure. I made my own out of hardware cloth (metal mesh).

Thomas Niedermeyer
MB hacker