Had to replace fan clutch due to a constant lockup condition. Of course many of you already know there's basically no room to work, hence the challenge in this otherwise simple job.
Tools:
MB lock rod tool, improvised steel rod(~5mm dia.), or chopped off sacrificial Allen key
10mm socket & 1/4" ratchet head
10mm GearWrench or similar (low profile)
8mm MB stubby socket, or Allen key cut down to fit (it's tight, real tight)
If using the Allen key, you will need some sort of cheater pipe for leverage
Blue Loctite
Start by pulling the two fan shroud clips on the right & left of the radiator, then pull the shroud up & over the fan.
Next, remove seven 10mm bolts from the radiator support, so you can pull the radiator forward a couple of inches for some working space. Take note of the threaded plates underneath the sheetmetal on top of the headlights. These plates will go loose after you remove the bolts, so you will need to slip your fingers underneath to line the threaded holes up upon reinstallation. The bottom bolt didn't have the clearance for a socket & ratchet, hence the GearWrench. A normal 10mm boxend wrench will also work.
Find the hole in the mounting flange behind the fan clutch; line the hole up with the ridges in the bearing bracket. There are several holes, but only two are properly sized and located to fit this piece of rod. You may have to fit your 8mm stubby socket or improvised Allen key tool to spin the fan clutch around until the hole & ridges line up. I got the lock rod tool from Performance Products; the tip was about 2mm too long to fit into the hole in the mounting flange behind the fan clutch. This may be because the fan bearing bracket might not be MB sourced(I had it replaced a while back, did not do it myself), or because exact design had changed a tad. Anyway I ground off enough of the tip to fit the tool. I used a piece of scrap wood wedged between the top of the radiator & the top radiator hose to maintain clearance. Turn 8mm fan clutch bolt anticlockwise & remove. It's a tight space, so just break it free then unscrew it with your fingertips or the socket head will hit the radiator fins.
Looks like I got to this just in time, what do you think? I was wondering where that mystery shrapnel I spotted on top of the air cleaner came from. Bearing self-destructed and the shrapnel was from the bearing cage, and hence the lockup. And I was driving this car around doing errands all this week! If I had let this go any longer the fan might have come off and annihilated the radiator. Seems I read of something like that happening to someone else.
New visco fan ready to be installed, note it's a Behr made in Germany. I don't think I would bother with a cheapo, but hey- this one might be bad off the shelf as well. Time will tell. At least it's bearing is new.
Transfer the plastic fan blade over to the new clutch and install; I used a little bit of blue threadlocker as I think I saw a little bit on the 8mm center bolt. Can't hurt. Torque to 33ft/lbs. Note that the new visco fan clutch may lockup upon installation, but run it in a bit and it will behave as it is supposed to. Mine ran for a few blocks despite a cold engine. Behaves as it should now.
This job's easy, just take your time & try not to gouge your radiator fins. Your hands will be chopped up & sore no matter what you do however. It would be grand if this writeup helps someone else. Do NOT wait to replace your fan clutch! If it's not working properly or roaring when the engine is cold, it's toast and it needs to be replaced. I have no idea how long I have been driving on a shot visco fan. If it freewheels, the internal fluid's gone. If it's locked as in my case, the bearing's gone. Deal with it before it deals with you.