You've probably got a new style tensioner as I do on my '95 wagon. The tensioner is just spring loaded; you just put a wrench on the front of it (I think 15mm), pull and hold while slipping off the belt.

__________________
as ever
Paul

1989 560SL
1987 300SDL
1987 300TD
1983 BMW 633CSi
1972 280SE 4.5