There two different clutch’s for the FMTV. Check to see if you have the fan that is attached with bolts or the one that is attached with nuts screwed onto studs.
What truck model and year do you have?
You can get a clutch rebuild kit, that’s what I did to mine, it works great and you don’t have to buy a new clutch. It’s not that hard to do just a little time consuming.
You need to remove the top radiator hoses (a small hose and a large one), intercooler lines, air line, the top fan shroud and fan to get to the clutch.
They say if you have the old style clutch that has the bolts that attached the fan you should replace place it with a the newer style that uses the nuts on studs.
Apparently the older one has a gasket that deteriorates and lets the fan wobble, which can cause damage.
I believe some of the smarter members on here can tell you more about the older vs the new one, then I can, and more!
Here is
@Ronmar, with a YouTube video explaining the old style. Great video.
Here are some photographs of the engine when I did mine.
Sorry, I didn't take photographs of the rebuild, I don't know why though.
Here is a video from Helicool's Helipad showing the fan clutch. Starts at 7:18
There are YouTube video's showing how to repair a clutch. This is the video I used before repairing my clutch. The only difference in this video, the fan clutch has a rear air seal whereas the FMTV's has a front air seal. You'll see that when you go to remove the air line to the clutch. Except for that it's the same repair with the correct kit.
I believe the kit I used was the 8000SKL, but check and verify that before you order one.
Kit Masters Part #8000SKL - Replacement for OEM Part #s: 9908401, 1681030c92, 10330543502, KMN208000SKL, ABPN208000SKL, FLT8000SKL, KMI8000SKL, 3443-8000SKL
kit-masters.com
EDIT: Just a note, after you take the front air seal off the front of the fan, remove the fan and replace the air seal so you can add air to the clutch so you can release the clutch and rotate the out portion to line up the holes to take the bolts out to get the whole clutch off.
Good luck.
Tom.