This post is about upgrading my 1980 W116 300SD to an 80 amp AL69X alternator and 9-blade fan with smaller pulley. Similar principles may apply in other chassis and models of Mercedes. Installing a 115 amp AL129X alternator should be the same procedure.

Since funds are currently very limited, I went around to the wrecking yards looking for alternators. The only vehicles with nice alternators had different wire connections than mine, except for old, nasty 55 amp ones like I had. I saw a couple nearly new Bosch Premium remanufactured 80 amp ones on two W126s, but unfortunately they were the kind that don't fit my car.

After going home and thinking about it, I decided I would make one of the AL69X 80 amp alternators fit. If I was successful, it would allow me to upgrade to a 115 amp AL129X in the future, if needed.

When I went back to the yard, I pulled both 80 amp alternators, which looked equally nice, and compared the two to see which was in the best condition. I was able to loosen the pulley nut one one, but the nut on the other one was so tight that the 8mm hex key socket spun inside the shaft, so that helped me decide which to purchase.

I also found a 9-blade fan and small fan pulley in a 1983 W126 300SD. The plastic 9-blade fan is lighter than the 6-blade magnesium one, and is supposed to take less force to spin, therefore will slightly increase fuel mileage. The extra blades increase air flow, and the smaller pulley spins faster, therefore causing the fan and water pump to turn faster.

The first thing to do is disconnect the negative battery cable to prevent sparks, component damage, and electrocution.


Then the two 17mm bolts and nut are loosened at the rear of the alternator.


Then loosen the belts by turning the 13mm tension nut counterclockwise.


I got tired of rounding out fan bolts, so I ground the end of my 10mm wrench so that the box end will fit over them.


Next, the fan and pulley are removed.

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DON'T MESS WITH MY MERCEDES!


1967 W110 Universal Wagon, Euro, Turbo Diesel, Tail Fins, 4 Speed Manual Column Shift, A/C
1980 W116 300SD Turbo Diesel, DB479 Walnut Brown, Sunroof, Highly Optioned, 350,000+ Miles