Edit: It does appear that a special hex 10mm tool is needed to loosen the mount that holds the A/C belt idler pulley. You've got to clear those two pulleys.

I'm trying to replace the belts on my 1986 560SEL. I'm having problems with the A/C belt. The belt runs over an idler pulley, which is this one:
http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1QV1B17JD1QV1CRHGJ&year=1986&make=MB&model=560-SEL-001&category=R&part=A%2FC+Idler+Pulley

The idler pulley is mounted to the engine with what appears to be a Torx or Allen-head bolt. From what I can tell, you "simply" loosen the bolt and swivel the pulley to remove or adjust the A/C belt. This doesn't appear to be a conventional spring-loaded "tensioner". Rather, it's simply a pulley on the end of a steel arm.

However, it appears impossible to use any conventional Torx or Allen wrench, since the Idler Pulley itself is partially in the way. I suppose I could remove the Idler Pulley first, but that doesn't allow me to re-tension the belt after replacing it.

FastLane shows two A/C Idler Pulley wrenches. It describes them as 10mm Allen Wrenches. (on Page 32)
http://www.peachparts.com/diy/mb_tools/mb_tools.html?cookieID=1PF1F75UP1PF1F7TC6&clientid=catalog.mercedesshop&cookieID=1QV1B17JD1QV1B17JC&source=www.peachparts.com&clientid=catalog.mercedesshop&source=www.peachparts.com&clientid=catalog.mercedesshop

Anybody know how to change the A/C belt on this car?

Thanks!
Myron Johnson
Tempe, AZ