Have you tried turning it yet? Go ahead and do as many people have already stated. Loosen the main bolts and then turn the tensioner 'knob'. Then report back.


I doubt you need a new bolt but if it does turn out you truly do I think I have an extra alternator bracket laying in the garage somewheres (in a pile of other Mercedes parts ).

I have seen both. The "thicker bolt part" attach to a nut and just screw in the bracket holding the alternator to the engine. You may not be able to see the 'rod extending down' from the 'knob' as it is covered by part of the bracket.

__________________
2009 ML320 Bluetec
1985 300CD
1981 300TD

Past Mercedes
1979 300TD
1982 300TD
2000 E320 4Matic Wagon
1998 E430
1984 300SD
1980 300SD

Nope, no bolt. I can see the entire bracket. I see the "knob" (it just spins freely). I see the adjusting channel in the bracket. There is definately no threaded rod or bolt already in it.

Is it possible to replace the "L" bolt while the alternator is in the car?

__________________
Big Fred

(RIP Sept '10) 83 300SD Turbo Diesel (aka "Rocky")
(RIP April '10 - Accident) 86 Chevy M1009 CUCV (Blazer) - 6.2L Diesel (aka "Ogre")

Clueless owners snap the small threaded arm all the time. When the break it, they don't want to buy a new one and the vehicle lives without it. Tension is generated the caveman way...........with a suitable crowbar.

The thicker bolt passes through the bracket...........through the alternator.........and through the bracket again on the rear side. It's secured with a nut on the rear side.

Forget about the older adjuster...............

I think you have just verified your problem of not charging. Looks like you need a new bolt as the belt is most likely slipping. Any pick n pulls around you? You can probably get a whole alternator along with the assembly for half of what you would buy the bolt new for. I'll check my pile of parts when I get home tonight.

Have you tried to spin the alternator by hand when the car is off? It seems that all signs are pointing to a slipping belt, but have you actually checked?

I'm sure it is possible. But since your belt is not tight anyways, I would just take it off to work on. I have found the extra time taken to prepare things (in this case taking the alternator off the car) properly save you time in the long run.

I can have an alternator off and on easily in 5, 10 minutes tops. It is simply a few bolts. The toughest part for me is getting the belts on. Just make sure the new tensioning bolt is as loose as it goes when you put the alternator back on the car. Then when you have it off you can take it to Autozone to have it bench tested to see if the alternator is actually good (I'm suspecting it is).

__________________
2009 ML320 Bluetec
1985 300CD
1981 300TD

Past Mercedes
1979 300TD
1982 300TD
2000 E320 4Matic Wagon
1998 E430
1984 300SD
1980 300SD

The belts are definately loose and although I haven't tried. I am positive I can spin the pulley by hand.

It is difficult to get to a pick a part during the day. (That whole work thing gets in the way of going to the parts yard)

__________________
Big Fred

(RIP Sept '10) 83 300SD Turbo Diesel (aka "Rocky")
(RIP April '10 - Accident) 86 Chevy M1009 CUCV (Blazer) - 6.2L Diesel (aka "Ogre")

That doesn't make any sense. If there were any current going thru the battery light bulb while the engine is running and charging the battery, it would illuminate.

I have read, as a side note, that when the alternator fails, all of the warning lights light up, except the SRS and CHECK ENGINE lights. The lights ground or earth thru the alternator durning the test phase of starting and when the alternator begins generating electricity, the lights lose their ground and go out.

You're right...it doesn't make much sense. That point was discussed also, as I researched ( I think somebody said something like..."I can't believe a tiny light bulb can take down the whole friggin' charging system" or something to that effect)... I only mentioned it because it was not a place I would have thought to look for a charging problem. I have not actually experience this problem myself. Here are two of the threads that mentioned the dash light. I think there were several more:

Not Charging...

No charging, but no battery light came on?

I didn't re-read those threads, but if they don't mention it, the dash light must be working, if I recall correctly, to complete the circuit which allows the alternator to be properly "excited" and, thereby, charge. It turns out Bigfred's problem was loose belts due to a non-existent/broken adjuster, I think. Hope he got it taken care of.

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-RK
'83 240D, auto, 170,000 miles "Old Blue"
'87 300TD, 140,000 miles

Went to the local pick a part lot on Friday. Actually found a 300 SD with the exact same alternator. I removed the entire assembly.

Took the pick a part alternator to AutoZoo and had it tested (checks good).

I decided to leave the alternator in my car and just replace the adjuster bolt. (Figured if it still didn't work, I had the pick a part alternator on hand already).

I installed the adjuster bolt and tightened the belts up. Everything appears to be working like normal!! I am reading 13.29V across the terminals when the car is running.

Thanks to everyone who helped!!

__________________
Big Fred

(RIP Sept '10) 83 300SD Turbo Diesel (aka "Rocky")
(RIP April '10 - Accident) 86 Chevy M1009 CUCV (Blazer) - 6.2L Diesel (aka "Ogre")

That is awesome. I'm glad you got it working.

__________________
2009 ML320 Bluetec
1985 300CD
1981 300TD

Past Mercedes
1979 300TD
1982 300TD
2000 E320 4Matic Wagon
1998 E430
1984 300SD
1980 300SD

Sounds good.

__________________
83 SD

84 CD