I'm not sure about your 99E300td but when I replaced the belt on my 98 E320 there was no need to remove the fan clutch.

I put a socket and wrench on the bolt for the belt tensioner and used leverage to take the tension off of the belt to remove it. Refer to your owners manual for a diagram for routing the belt.

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Ray
1998 Mercedes E320, 200K Miles
2001 Acura 3.2TL, 178K Miles
1992 Chevy Astro, 205K Miles