How to adjust alternator on 85 300 SD

I am trying to tighten the alternator belts, as they are squealing very badly. Have to do it from below, as the turbo blocks it from above. I loosened the upper bolt that slides along a "channel", and the lower bolt a
little, too. Just above the alternator there is something protruding on the the top outer side of the alternator (as I look up from below), hex-shaped, and about an inch or two long. I thought this would be the tensioner, but when I try to turn it with an open-end, it doesn't turn freely.... it twists a bit with lots of force, like I am going to snap it off. What am I dong wrong?
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On my 83 300SD I kind of recall having a similar problem. Look real hard and I think you find another nut that needs to be loosened. Perhaps someone with a manual or better memory might chime in.
--

73
Hank WD5JFR

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I just did this job on my '80 300SD. It's good that you stopped for you're right, the hex nut is the tensioner and works very well once the alternator's security bolt is loosened. Specifically, the 17 mm bolt at the rear of the alternator that's AWAY from the engine's block (there are two bolts about 2" apart). The 17 mm bolt is accessed from the bottom. Then, from the top, turn the hex nut clockwise to tighten the belts. Then tighten the security bolt.
Replacement belts ought to be a matched set for their slightly different lengths will make them work against each other and so develop a glaze.
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also do not over tighten to do so will give you experience in changing water pumps.
the 2 pulleys help take the load off the bearings & seals.
the case, minus a few cans!
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