What fluid does everyone use in their manual transmission?
 

My understanding it that Mercedes originally said 10w oil but now will tell you to put any dextron in it (yes, ATF).

Has anyone trie MTF or anything else?

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IMHO any quality 75w80 is ok.

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YOU USE 75W80 IN YOUR MANUAL GEAR BOX?!?!

Wow! They make good coffee in Pennsylvania, I guess.

Thats a HUGE difference from ATF. I didn't think that would work at all. How does it shift?

Answer
 

1980
240D
Four speed manual transmission.
Dexron/Mercon III (ATF).

I flushed out the previous thick sludge, three times before it shifted correctly..

In sub-zero temperatures, the previous (guessing) 80/90 gear oil prevented shifting, and/or gummed up the synchromesh = grinding in all gears.


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I'm thinking of going with Red Line D4 ATF in mine (82 240D 4 speed), but haven't decided for certain yet. I'm not going to be changing it for a couple weeks, waiting until it will at least be above 40 outside.

I used Mobile 1 Synthetic ATF and works fine. MUST smoother. I ran some cheapo stuff to flush it out (Autozone). Drained, and put the good stuff in. I think the Haynes manual indicates AFT, also.

I just refilled mine with Penzoil "Syncromesh". I have been satified with Dextron, but this is a newly designed oil for these constant mesh transmissios. I have heard good things about, so I am using it.

DO NOT use 75W80. use ATF or 5W20

You can use a MB 235.1 approved 80W gear oil, but ATF was prescribed.

This is incorrect. 80 weight oil is fine for the axles, and the differential, but the manual gearbox needs a thinner oil or the syncros will not function.
5w20 should work, straight 10w, any quality ATF or preferably a synthetic ATF...

80W gear oil is as thin as ATF.

Oil weights aren't absolute numbers.

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Um, I'd need you to show me some documentation for this... weights of oils are a standard of viscosity universal across all brands and types of oil... oils with the W in them between two numbers, are manufacturers multi-viscosity oils, and can vary from temp to pressure and useage...

ATF is in the 10W range...