How to adjust alternator on 85 300 SD

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Jimbo - 13 Mar 2005 14:25 GMT

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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Henry Kolesnik - 13 Mar 2005 15:50 GMT

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.

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73
Hank WD5JFR

>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
[quoted text clipped - 9 lines]
> a bit with lots of force, like I am going to snap it off. What am I dong
> wrong?

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T.G. Lambach - 14 Mar 2005 01:36 GMT

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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pool man - 14 Mar 2005 02:55 GMT

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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