My alt has been making some rattling noises. I looked at it as the car was running. The pulley looked like it was wobbling a little.

When the car was off I could move the pulley a little. I felt the shaft that holds the pulley on and it was threaded but there was no nut...???????

Is the pulley pressed on? Is there supposed to be a nut there? Why hasn't the pulley fallen off?

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'85 300SD (formerly california emissions)
'08 Chevy Tahoe
'93 Ducati 900 SS
'79 Kawasaki KZ 650
'86 Kawasaki KX 250
'88 Kawasaki KDX200
'71 Hodaka Ace 100
'72 Triumph T100R

The exact same thing happened to me on the way home with my 300SD when I first bought it. In my case, the nice folks at NAPA had not tightened the nut on the shaft tight enough when the PO bought a new alt and they swapped the pulley from the old alternator, and it must have come loose.

There should be a nut on there and a woodruff key (little 1/4 moon shaped piece of metal that fits into a grove on the shaft and alternator) to hold it in place. The pulley hadn't fallen off of mine either, and it was a 90 mile drive. I think the tension of the belts kept it relatively inline, though the alternator was probably doing next to nothing.

Chances are you will need a new alternator because the shaft is probably messed up from having the pulley rattling around on it (that was the case for me anyway)

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I got everything off and the pulley, washer and fan fell off in my hands. The woodruff key was a little ragged looking as well as the channel that it slides into. I slid everything back on the shaft and it looks like it is still serviceable. I am going to drop it off have them clean it up, test it and give me their opinion.

__________________
'85 300SD (formerly california emissions)
'08 Chevy Tahoe
'93 Ducati 900 SS
'79 Kawasaki KZ 650
'86 Kawasaki KX 250
'88 Kawasaki KDX200
'71 Hodaka Ace 100
'72 Triumph T100R