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

Don't loosen the allen bolt. The pulley is attached to a short bracket which then bolts to the engine. Use 19mm open end wrench to loosen the bolt that holds the bracket to the engine. You won't have to loosen it very much to cause to bracket to swing down. The belt can now be removed and replaced. The real trick is applying leverage to the pulley assembly to tighten the belt while tightening the 19mm headed bolt. They make a tool for this that uses the allen bolt that holds the pulley but you should be able to apply leverage to the bracket that holds the pulley with a combination of a short prybar and 22mm open end wrench to the bracket. Mark

The tool you are talking about if I'm not mistaken is here. http://www.peachparts.com/shopforum/showthread.php?t=126728

It's been a while since I've done this job but as I recall you loosen a bolt and then use the special tool to hold the pulley where you want it, i.e., to tension belt and then tighten the bolt.

Edited:
Or you could buy the tool here http://www.samstagsales.com/mercedes.htm it's $57.95

FYI, I noticed this little aberration a few years ago: a standard box end wrench was just'a little bit too thick to get in between the pulley on the tensioner and the bolt.

Solution: just grind (I used a Dremmel) a shallow recess on the interior side (typically the side angled "in" vs. the side angled "out") that allows you to slip the box head between the two.

I found I had to use a hammer to initially break the tensioner bolt free (I think the OFFICIAL MB-Approved tool has about a 4 foot handle and the "boys" crank on that baby like it was a RR track switch!!)...

"Tap, tap, tap, (Curse!) tap..... Ah!

There is also a "flat" on the tensioner arm where you can put an adjustable wrench (if it is skinny enough) or an open-end wrench to put some tention on the belt by lifting up. There is room (at least there is on a 420SEL) for both your hands and the two wrenches.

I have one of these at both houses because you just don't know where a belt will break. You can drive a bit without a/c, air pump or even the alternator belt, but not far without the water pump and p/s belts.

Cheers!

__________________
'91 420 SEL @ 199K, '92 SVX @ 181K, '93 SC400 @ 86K, '93 Kaw ZX-11 @ 30K, '87 F250 @ 181K , 2001 Valkyrie Interstate @ 6K, Y2K Honda NightHawk 250 with 1.5K, '88 420SEL I.@ 179K & the 2nd latest, an '88 420SEL II.@ 210K runnin' parts car, '85 F150 300/NP435