RE: a 1985 300 TDT (or any other car for that matter). Removing the fan & pully from the old alternator is easy - impact/air gun - short trigger-pull and the nut's off. How are you supposed to tighten the nut holding the same fan and pully to 70Nm?? Actually, how are you supposed to tighten the fan and pully at all? Obviously the whole assembly just spins both directions with no resistance. There's only the threaded stud and a nut. Nothing to hold onto to torque it. You CANNOT put something in the blades of the fan to hold it steady (like a screwdriver), the blades will bend - guaranteed.

Use the same impact wrench, At least that is what I did on my daughters 240D.

Dave

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1970 220D, owned 1980-1990
1980 240D, owned 1990-1992
1982 300TD, owned 1992-1993
1986 300SDL, owned 1993-2004
1999 E300, owned 1999-2003
1982 300TD, 213,880mi, owned since Nov 18, 1991- Aug 4, 2010 SOLD
1988 560SL, 100,000mi, owned since 1995
1965 Mustang Fastback Mileage Unknown(My sons)
1983 240D, 176,000mi (My daughers) owned since 2004
2007 Honda Accord EX-L I4 auto, the new daily driver
1985 300D 264,000mi Son's new daily driver.(sold)
2008 Hyundai Tiberon. Daughters new car

Tighten the nut hand tight then reinstall the alternator and drive belt. Press on the drive belt to hold the pulley and torque the nut to 70nm.

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Fred Hoelzle

I didn't think of that.

If you go with the impact wrench to tighten the bolt, try to reduce the torque. Napa just changed a pulley for me and broke the hole out with excessive force. One possibility is to adjust the impact wrench torque off line and check with a torque wrench. The orginal Mercedes pulley was very weak around the bolt hole. The pulley that came with the rebuilt was very substantial although a little smaller than the original. Still worked ok within the range of the belt, spring and shock. This on a 87 300dt.