Older thread, but I'm trying to tackle the same project. My 1994 E320 wagon has a 6MM bolt holding the tensioning pulley (#7 in the picture):



I am able to loosen the bolt in the middle of the tensioning pulley.

Next my understanding is that I need to loosen the tension with the adjuster shown in this picture:



Which way loosens the tension? I've read both clock-wise and lefty-loosey. It seems like lefty-loosey (counter-clockwise) would be the right way, but how far does it usually need to be loosened? As soon as I turn it counter clockwise it the adjuster fells pretty loose but the belt doesn't seem to be any looser.