1999 E300 alternator pulley gone AWOL - PeachParts Mercedes-Benz Forum

Sbean · #1 12-12-2008, 02:14 AM

Tonight my wife was in town in our '99 E300 turbo (210 k miles) and experienced strange noises from the engine, and dashboard lights complaining something about "battery" with a picture of a battery; she parked safely. From her description over the phone I guessed it had to do with the serpentine belt. I checked it out and found the belt unbroken but lying loose. The pulley had come off the shaft of the alternator and several fan blades are broken. The pulley was lying below the alternator.
Tomorrow I plan to call a mechanic I know (Independent Mercedes Master technician on his own after 30 years at the Monterey dealership) whose shop is just a few blocks away, look at it and advise if it's feasible for me to work on it myself. I'm wondering if the alternator shaft is damaged enough to require replacement. I don't know what is supposed to keep the pulley on the shaft, or what might cause it to come off. Looking at the pulley and shaft I didn't see any key or anything to prevent it spinning on the shaft. I guess there might be a retaining bolt, but I didn't try feeling the end of the shaft. Tomorrow I will.
Does anybody here with more experience on the OM 606 have any comments? Thanks. Steve

KarTek · #2 12-12-2008, 05:22 AM

Steve, are you seeing a threaded part on the end of the shaft? Or is there no shaft sticking out where the pulley was? I'm guessing the pulley is held on by a nut and the shaft is slightly tapered to keep it from spinning.

I'll look at my car this morning and see if I can tell anything.

Matt L · #3 12-12-2008, 10:32 AM

The pulley is not fixed to the shaft. There is a ratchet between them. Apparently yours has failed.

KarTek · #4 12-12-2008, 10:36 AM

A ratchet? So it allows the alternator to over-run the drive pulley? That's interesting. Sounds expensive... Any idea why they chose to do it this way?

Matt L · #5 12-12-2008, 10:39 AM

The alternator may over-run the drive pulley at idle, due to the high compression of the engine. It should not happen at speed.

It really doesn't seem like it should be a problem to have the alternator speed vary with the engine. All that I can think of is that they may get a higher idle output when using the ratchet.

Sbean · #6 12-12-2008, 10:49 AM

Thanks, Evan and Matt,
I saw no threads. Both the shaft and the pulley bore looked somewhat worn or galled. I'm about to phone the mechanic to arrange towing so he can see it and it won't get ticketed. It's legally parked on a city street but there is probably a time limit. Then I may get it towed to my house or have him repair it if it needs more than I can take on.
Steve

KarTek · #7 12-12-2008, 10:54 AM

How many miles are on the car? This is the kind of thing I'd hate to happen on a long trip with service options limited...

Sbean · #8 12-12-2008, 11:50 AM

The car has about 210,000 miles on it. I talked to Charlie, the mechanic, just now and he said these cars had this problem often enough that he used to routinely torque the retaining bolt on them when new. He said it sounds likely the alternator will need replacement due to damage to the shaft. I'll know more when he sees the car. He said there is are two special tools involved- a socket for the bolt and one to hold the fan. I didn't ask him yet if they are essential to do the job.
Steve

TMAllison · #9 12-12-2008, 11:54 AM

Suspect he is referring to the fan clutch. Uses a low profile socket and another tool to hold the clutch from rotating as nut is lossened.

Sbean · #10 12-13-2008, 01:48 AM

That's right, Terry. I'm letting him do the work. It needs an alternator, fan, pulley, and might as well give it a new belt, and keep the old one as spare. He showed me it's pretty easy to put the belt on.

F18 · #11 12-13-2008, 01:06 PM

Lucky your wife was close to home and your Indy!
I had a woodruff key let go on the pulley of the 84 300SD a number of years ago in Northern Maine. The pulley did not do much damage but it dropped out of the bottom of the engine compartment and squirreled down the road in front of me. Had to have a foreign auto mechanic on a country road overnight air a replacement alternator with pulley plus spend an extra night in a hotel. I could have bought 4 alternators for what that one failed Woodruff KEY cost me.