Found loose belt due to loose alt pulley bolt on my 300sdl, I know its 8mm but how do I get alt to stop turning to tighten it up? The fan blade behind pulley I believe is what chewed up my last belt, don't know why the guy I had put new vacuum pump and belt on didn't notice. Anyway I decided I could do it myself and try it with alt in car. I've taken off metal fan blade for better access, upgrade on that someday. Any ideas, doesnt seem to be keyway that I can tell to hold fan and pulley in place while tightening. Best I can tell its a friction fit, I just have to figure out how to keep alt from turning. Any help appreciated. Thank You

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86 300SDL

On further examination, I've found that the 8mm inset is surrounded by big nut. So now more questions of how to tighten it or do I have to remove entire altenator and tighten it on bench?

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86 300SDL

I have a 86 300sdl. I bought a used alternator for it and installed it and after 5 miles of driving the belt came off. The pulley had become very loose on the alternator. I got home and took the alternator off and found the woodruff key missing. I ended up taking the new brushes out of the used alternator and putting them in my old alternator and put my old alternator back on.
I then put the used one away and forgot about it.
Moral is... there is a woodruff key that helps hold the pulley to the shaft. Make sure you have not lost yours.

John

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John
1986 300sdl
1985 380se

Be sure and check the shock absorber on the belt tensioner whenever you have alt pulley issues!!!!!!!! I went through 4 pulleys and an alt on my first experience with a bad one. The defective shock allows a vibration to be set up in the belt and causes the pulley to fail.. or maybe even loosen up.

If you have access to an impact wrench.. that will sock the nut down tightly, and is the best way to do it. If not.. then you need sockets that are open to insert the allen key into to hold the shaft tight while you tighten nut.

I assume of course you have a serpantine belt as opposed to the double V belts?

Well I thought I had it tightened, put everything back together and it all loosened up in 2 miles so I limped back home. Guess I will have to take it out of vehicle get woodruf key and tighten it better. That or get a rebuilt alt. Thanks for info. One good thing to come out of this, the upgrade for fan and clutch will be a cinch. Any tips to take alternator out or just a matter of unhooking battery and electrical connections and 2 bolts holding it on.

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86 300SDL

Pulling a 603 alternator is bit of a puzzle. IIRC the easiest way is to hang the shroud on the fan and pull it up along the right tank of the radiator. Or maybe it's in a 140 that it's a puzzle.

Most rebuilds don't come with a pulley or key.

Sixto
87 300D

When the bearings went on the '86, I recall that it was not difficult to remove from underneath the vehicle.

The new alt. came with no key, and the old alt had no key. So, the impact wrench had to suffice...........

Removing the alternator from below is a 15-minute job on the 603 in the 124 chassis, I suspect that the 126 is the same.

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Gone to the dark side

- Jeff

Must be the K-frame 140 crossmember I'm thinking of.

Sixto
87 300D

You will not find a woodruff key slot on any car alternator that i have seen or in the pulley either. Make sure the pulley is a good fit on the shaft,that it has not worn the shaft or pulley from being loose.When you are sure the fit is good(it should push on by hand but once it is all the way on NO perceptable play between shaft and pulley) The best way is with an impact wrench but if you dont have access to one you can use a box wrench for the big nut and an allen wrench in the end of the shaft to keep it from turning,get it as tight as you can and then check it againg after a few miles. Don

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Red Green "This is only temporary,Unless it works!"

97 E300D 157000 miles
87 300TD ?141k? miles

I cannot agree with the the first part of the above statement here is a pic of parts of my Alternator show that the parts have the slots for the Woodruff Key and I believe that is the key is between the Fan and the Washer.


Impacts Wrenchs work great on stuff like Alternators (if your are in doubt use Blue Loctite on the threads when you install the shaft nut). Most often the Impact Wrench will snatch of the nut with no need to otherwise hold on to any thing. When you assemble; run the nut down (with Loctite on the shaft threads) by hand as far as you can and squeeze the trigger on the Impact. When that alternator starts to rotate stop squeezing the trigger and let it stop and repeat the process 1 more time.
While I have an Air Compressor and Pneumatic Impact Wrenches I most often use a 12 volt battery powered one that I got from Harbor Freight (when on sale are about $21, I bought 1 for each of my 4 vehicles) that are sold for dealing with the lug nuts during a Tire change but can be used for most everthing a regular Impact Wrench can be used for. Clip it to the Car Battery or pug it into the Cigarette lighter socket.
Besides replacing a Pneumatic Impact wrench it speeds up and makes tire rotation easier.

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84 300D, 82 Volvo 244Gl Diesel