I'm working on my 1982 300CD, alternator with two belts and the 90 degree threaded bolt w/nut adjustment system.

Seeing how one of the alternator belts broke, I figured it was time to throw a couple of new ones on. PS and AC came off just fine. Alternator hasn't been so easy.

Upper 17mm nut unscrewed just fine (the nut in the back since the bolt head has the threaded adjustment rod welded to it).

The small 10mm nut and washer on the rod are off, and the rod can travel freely through the bracket it's (loosely) fitted through.

Lower 17mm bolt (the one the alternator rotates around) loosened after much pain, fear or rounding the bolt head, and finally some much-appreciated help from the folks at the local Goodyear. The bolt is loosened but not all the way out.

The alternator will now move on the adjustment bracket, but I can see that it isn't moving all the way in towards the motor, and the travel it has right now isn't sufficient to slip the remaining belt off, and I don't think it's safe to try to cut it off and try to get the new ones on (logic suggests that if the old one won't come off, the new ones won't go on).

Is there a bolt I'm missing? Some kind of adjustment system I haven't taken into account?

Thanks to anyone who has a suggestion...

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1992 300D 2.5T 249k - Parked with a bad transmission
1981 300SD 142k - Daily driver

Sometimes you can force the belts off when you have gone as far as you have. If not, there are three bolts on the alternator, one is at the block where the alternator adjustment rig bolts on (you don't have to take out the bolt that holds the alternator to the adjustment rig). If you take that bolt out, the body of the alternator (with the adjustment rig still attached) will drop down and you can change the belts. Once the belts are in the pulleys, the alternator will slip back into place. When it's bolted back in place, use the adjustment bolt to tighten the belts.

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Houston, Texas
1984 300CD 235K miles, Elvira, one owner
1987 300TD 180K miles
1974 TR6 78K miles Sarah Jane, one owner
OBK #27

When I changed my belts, the ones the store gave me were too short. I refused to remove the alt to get the belts on it. got a longer belt and it worked great. If the adjuster is working and all of the way in, I would guess that the belts on it may be too short, and you may have to remove it to get them changed.

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83 300SD Dark Silver Dark brown inside

The SD has the same problem with the 1000 mm belts. IMHO, the size is incorrect and 1015 mm belts should have been utilized.

You can remove the water pump pulley (and fan) to get the belts in place and then reinstall the pulley.

Or, you can set the belts up so that they will engage the sheaves when you turn the starter.

Naturally, the old belts are cut and removed.

That third 17mm bolt in the back was completely inaccessible until I removed the EGR heat shield. (I should probably do some off-road testing without the EGR just to see how it runs without one.) Once it came off, though, all was well and it went smoothly. Of course being the idiot that I am, I left the belts too tight, (they're squealing) so I'll have to go redo the whole procedure tomorrow to loosen them up a bit. Still, worked like a charm.


Thanks 123guy, blackestate, and Brian for the help!

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1992 300D 2.5T 249k - Parked with a bad transmission
1981 300SD 142k - Daily driver