99 E300 Alternator help
 

Hello All,

I was driving my 99 E300 yesterday when all of a sudden the Battery light on dash came on. I was about a mile from home so I decided to keep going to see if I can make it home. I was almost there when I noticed that I lost my power steering. When I got home, I opened the hood and I saw that the serp belt had popped off. I looked around to see what caused it to pop off and found that the alternator pulley was loose. I was able to just slide the pulley off of the alternator. I'm not a mechanic, but I'm guessing that I shouldn't be able to just pull off the pulley, right?

Does this mean that I need a new alternator?

You need to put the pulley back on the alt and tighten it down with the nut, hopefully you can find it in the engine compartment. Will the fan on the alt turn freely?

I can't find the nut. There's a rubber cover that is on the outside facing part of the pulley. The rubber is still intact, so I'm not sure if there was a nut that came off. If the nut would have come off, then it would have broken that rubber cover.

Are you sure there's a nut?

Pulley Nut
 

http://www.detali.ru/cat/oem_mb2.asp?TP=1&F=124131&M=606.910&GA=722.435&GM=717.433&CT=M&cat=19T&SID=15&SGR=030&SGN=02

#510 if it's a Bosch (MB part #000 990 22 50)
#710 if it's a Valeo (MB part #000 990 22 50)

[Oops,somebody at the factory goofed,they're both the same nut]

When you go to re-install the nut (New or the old "Lost" one) use a Rubber
or Fabric/leather "Strap" wrench to hold the Pulley when you "Torque Down" the Nut.
[Don't use "Vise Grips" or any other kind of gripping pliers...you'll screw up the Pulley's finely machined grooves...which will,when damaged,harm the belt]

Harbor Freight has a cheap set of Rubber Strap Wrenches $4.99+tax:

On my 99 E300 (200k miles) the pulley came off completely a few months ago and damaged the alternator shaft and broke a couple of fan blades, requiring a new alternator and fan. The cause appeared to be that the bearings in the pulley froze up. From the way things must have been thrashing around down there, I think I'm lucky the radiator wasn't damaged. The pulley contains a clutch of some kind and roller bearings. My mechanic, who has 30 years of experience at a Mercedes dealership, has seen it before, and says he used to tighten this pulley on every one of these cars that came into the shop. Steve

When you put the Nut back on use a little Loctite.