I'm stuck. I got a new alternator for the 87 300D. The alternator pulley has to be removed from the old alternator and installed on the new one. It has a recessed nut (7/8 or 15/16 six sided), and a 8mm allen head hole in the shaft.
It appears that you have to put a socket on the nut, which is right-handed,
and an allen head in the shaft hole at the same time. After looking at it awhile and trying a couple things that didn't work, I put a 3/8 drive socket with an 8mm allen head driver in the shaft hole, put a 1/2 inch deep impact socket on the nut, and put a 3/8 extension through the 1/2 inch hole in the deep socket. With a pipe wrench on the socket and a socket driver on the 3/8 inch extension, I wrestled with it. No luck...not even having the pipe wrench on the ground and me standing on the socket driver. Do you have any suggestions about how I can get this hummer off? Thank you!

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1987 300D with 201k miles.
1985 F350 Ford dually 6.9 diesel
1988 F250 Ford utiilty truck 7.3 diesel

That's a job for which an impact wrench is well-suited. Usually, a helper can hold the pulley well enough that you don't need to hold the shaft. A little penetrating oil might help.

Thanks for the input...you were correct. The impact wrench was the answer. Quick and effective. Place alternator on the ground. Place foot with shoe on the fan blade while using impact wrench. Three seconds and off.

__________________
1987 300D with 201k miles.
1985 F350 Ford dually 6.9 diesel
1988 F250 Ford utiilty truck 7.3 diesel