Anyone have any tips for putting new alternator belts on my 1983 300CD? It only had a single belt when I bought it and I figured I'd go ahead and replace it and add the second belt while I'm at it. There doesn't seem to be an easy way to do it without removing the AC and power steering belts.

I just did this with my 78 W116 300SD.
All the belts have to come off to install the alternator/water pump belts.

The FSM link is here:
https://www.startekinfo.com/StarTek/outside/12265/disc_2/program/engine_82_co.htm

Group 13 is the Belt drive section.

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78 W116 300SD 'Desert Rose' new as of 01/26/2014
79 W116 300SD 'Stormcloud' RIP 04/11/2022

Unless 'abra cadabra' & a wave of the magic wand works, you will have to remove all the belts. Now is a good time to replace them all. BTW tho it seems obvious, it is important that the alternator pulley is aligned with the crank, otherwise you will lose one or both belts. A long straight edge helps with the alignment.

Years ago it was easy to get a matched set belts that were of extremely close, if not identical length and sold as a "matched" set. When two belts are on the same pulley they will have different tension if they are not the exact same length. If you can, go to a parts house that will let you measure and compare all of the belts they have in stock for the size needed, look at the lot numbers on the belts and get the two closest ones. You may also be able to measure them on a belt gauge at the store.

This is one of those small things that "makes the difference" and looking at that job you will see doing it once is too much

When installing the new belts line up the numbers and labels and it will be an indicator if one is slipping if the numbers no longer line-up.

Good luck!!!

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

For how long have you seen the labels stay aligned? I would think after 100 miles of driving it would be very unlikely, but haven't tested it. There must be some differential inch-worm motion even in the most perfectly matched belts.

I am guessing the dual belts was so you wouldn't get stranded on the road. U.S. cars of the 70's w/ similar alternators usually had a single belt. I also carry nylon rope in my vehicles, so in an emergency I can tie it (barrel knot) to turn the just water pump to get home. It would be very hard to remove the AC and p.s. belts on the side of the road to get at the alt belt. If not driving at night, you don't need the alternator to get home w/ a diesel.

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans

If your belt adjuster is damaged,you will have to do it the old way.Lossen bottom good,and all bolts,have some one use a crow bar to hold alt,while you tighten.

"For how long have you seen the labels stay aligned? I would think after 100 miles of driving it would be very unlikely, but haven't tested it. There must be some differential inch-worm motion even in the most perfectly matched belts."

Bill I didn't keep track of it and yes eventually they probably did start to mis-align.

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

If anyone else needs info on the W123 Alternator - check out the DIY article below.

Mercedes-Benz W123 Alternator Replacement | 300TD 1977-1985 | Pelican Parts DIY Maintenance Article

To ease the removal of the alternator, remove the adjusting bracket and alternator as a unit then separate them later. Same with the installation. This will prevent bent and distorted adjusting bolts.

Also, for dual belts, get them from the same lot# or the tolerances for length will give you problems. The lot# is usually printed on the side of the belt.

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Sam

84 300SD 350K+ miles ( Blue Belle )