Poking around the engine today, tracking down rattle and noticed the alternator's missing a bolt...

I cannot find consensus regarding the appropriate size, anywhere.

Can anyone help me out here?

The specific bolt I'm referring to:

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1981 240D 4sp manual. Ivory White.

Up

Gotta get this car back on the road by the weekend.

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1981 240D 4sp manual. Ivory White.

Dang, I replaced the same bolt 6-8 month ago. I took the old one with me to a fastener supply place an matched it up. It is a metric size, that is all I remember. Both the bolt and alternator housing were worn and rattling around. Had to replace both upper and lower bolts and the alt both since the pulleys would not stay aligned. I think I have the old ones laying around, a tape measure may get you in the ballpark. I will have a look later today.

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1985 300D
The rest:
1957 MGA (comatose)
1965 Falcon (sleeping)
1966 E-100 (rust test in progress)
1976 Ford 3400 D Tractor (workhorse)
1978 Mercury Zephyer (5L playtoy)
1995 Isuzu NPR D (fetcher)
1998 Subaru Legacy (Spare)
2000 Toyota Sienna (School bus)
2008 Toyota Prius (Commuter)

I believe it is an M12 bolt size with an 18mm head (socket size). The length is approx 5 and one half inches. I believe it is a course thread (1.75). You will need to find an auto hardware specialty store/house to source the bolt. Bolts from home improvement stores (home depot, lowes) are not strong enough for automotive use.

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I believe this is the actual bolt you need though I'm not 100% sure. belmetric offers various hardness of steel. I'm unsure which is the correct hardness for the alternator. I measured mine and it is five and a half inches. that translates to a length of 140mm.

https://www.belmetric.com/12x175-coarse-c-506_510_399/bh12x140ylw-hex-bolt-yellow-zinc-109-p-3841.html?zenid=s1irauv450kl5e07rinbcui8p4


You could also try your local mercedes benz dealer's part's department. I'd check there first. Probably best to order several so that you have spares on hand.

Thanks for the replies gents.

I've read m10 with a 1.5 pitch, 120-125mm in length...
I've also read m8 at 115mm.

I think it's the same bolt as the upper bolt?

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1981 240D 4sp manual. Ivory White.

Call your local MB parts department and ask to speak with someone that knows your year, make of car. They have a computer system and can look up the EXACT bolt size for your car. I've had the best luck physically going in person to play the game known as "look up parts on the big mercedes benz computer system".

Looks like there were 3 bolts all the same 125mm. Edit: Yes, one of them had the adjuster, it was broken as well. I think the host site here has a replacement part.

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__________________
1985 300D
The rest:
1957 MGA (comatose)
1965 Falcon (sleeping)
1966 E-100 (rust test in progress)
1976 Ford 3400 D Tractor (workhorse)
1978 Mercury Zephyer (5L playtoy)
1995 Isuzu NPR D (fetcher)
1998 Subaru Legacy (Spare)
2000 Toyota Sienna (School bus)
2008 Toyota Prius (Commuter)

Well, with a plan to compare the remaining bolt to a new one, I removed the alternator.

The old one snapped in the pivot mount -who knows when.
The mounting bracket itself was also cracked at the hole the adjusting bolt passes through.

I posted in For Sale, but if anyone reading has an alternator bracket FS, can you DM me?
Currently in Northern California and I need to be back on the road by the weekend.

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1981 240D 4sp manual. Ivory White.

Welding shop or friend with a welder may be able to patch the crack well enough to get you back on the road. 5 minute job since the part is off the vehicle. Depending on the position of the crack and/or skill of the welder it could be a 'permanent' repair. Good Luck!

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1985 300D
The rest:
1957 MGA (comatose)
1965 Falcon (sleeping)
1966 E-100 (rust test in progress)
1976 Ford 3400 D Tractor (workhorse)
1978 Mercury Zephyer (5L playtoy)
1995 Isuzu NPR D (fetcher)
1998 Subaru Legacy (Spare)
2000 Toyota Sienna (School bus)
2008 Toyota Prius (Commuter)

That's a very interesting idea, thank you

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1981 240D 4sp manual. Ivory White.

This is a good idea if you can't make it up to Reinvent the Wheel or to connect with our friend in Medford...

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1983 300D Midnight Blue
4 speed, W115 intake mani, non-EGR exhaust mani, KKK K26, 3 pc Euro bumpers, Lo-spec Euro headlights, AL129X, hubcaps, custom A/C

1987 300TD Smoke Silver
Euro headlights, thermostat relocation, coolant bypass mod, rebuilt Becker + Jehnert + Helix audio, OEM Oris roof boxes and surfboard racks, Euro towbar

1983 300TD Reed (Moss) Green / Dark Olive MB Tex Euro spec

1983 300TD Silver Blue / Blue cloth Euro spec, OM648 and 722.6, 15" hubcaps, W126 S2 brakes

Upod is actually posting me the part -relief- but I am curious about repairing the original plate if possible. Wouldn't hurt having a spare...

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1981 240D 4sp manual. Ivory White.

You may be interested in the following thread - I had similar problem. Kind soul here helped me out with the correct bolt (Thanks again Rollguy!)

http://www.peachparts.com/shopforum/diesel-discussion/395282-w123-85-300d-alternator-pivot-bolt.html

You will see that there are two types of bolts. One just threads into casting, the other goes through and has a locknut.

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

Thanks Graham, I had read your post.

Oddly, mine did not back out, it broke (and then backed out). I had to drill out the nub threaded end that remained. The new bolt I have installed protrudes enough for a lock nut... hadn't thought about it, but might just put one on for good measure.

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1981 240D 4sp manual. Ivory White.