1988 300SE Repalced the A/C compressor. WE loosened the tensoner nut and fan belt came off no problem. This is a three month old tnsioner and shock that were replaced with the water pump (an enlighting experience).
When we put the fan belt back on and tightended the nut it just turned and turned no belt tension.
Looks like from drwaing that this is two peiceces on the threaded rod. We have at least 1 inch of rod past the top nut and both seem to be turning.

Can any one please advise what to do.

We have stopped for this frustrating day and are looking at trying to break the two nuts part and or loosed the 19 MM nut in front of tensioner.

HELP

Thanks Brian