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  #1  
Old 04-03-2011, 04:03 AM
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Transmission compatibility question: what transmissions will work on my 81 300D?

Hi everyone. I posted this a while back on one of the other MB forums but there weren't any takers. I am new here, but this is now certainly my favorite forum due to the technical knowledge that is here...so I have a feeling some people will know this easily.

I have a 1981 300D with a 123 722.1 transmission that flares from 2-3, otherwise works well. I am, say, 75 to 80% certain my vacuum is in order. I've also changed the fluid and filter. I have checked the modulator line and it doesn't leak vacuum, but I haven't tried adjusting it.

I have access to a 300k mile 116 722.1 transmission from a parts car, a 1980 w116 300SD. The transmission is sitting there waiting to be picked up. I also know that some people around here have a later 1980's 722.3 or 722.4 from a 300D Turbo.

Some people tell me the 116 one won't fit since it is not for the same body style, some tell me the 300D turbo won't fit since my 300D is not a turbo.

Ideally I would be able to buy a transmission from an 84 or 85 that would be newer and hopefully work better than the old 722.1. Or, perhaps some of you will tell me I should fix mine.

Just wondering what your thoughts are, and if I should try finding another transmission, and, if so, which ones I can safely use.

Thanks!

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Last edited by sshanky; 04-03-2011 at 04:17 AM.
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  #2  
Old 04-03-2011, 10:07 AM
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If it helps to know, my 84 300D non turbo has a trans meant for a turbo in it from new. I believe the main differences would be the trans cooler lines in the non turbo are smaller. The later trans have different setups for their bowden cable connection to the throttle linkage. The inhibitor switch may be different as well.
I would try adjusting the modulator until the other changes were becoming harsh, if that didnt fix it then swap the trans out.
A 300k mile trans may be on its way out as well.
If you have access to a good second hand trans that would be a safer route than trying to rebuild yours unless you have rebuilt auto trans in the past.
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1980 300D now parts car 800k miles
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1987 250td 160k miles English import
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Old 04-03-2011, 10:37 AM
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It wouldn't surprise me that a 722.3 will fit, but they have a Bowden cable, a 722.1 does not.

The control pressure rod is a solid affair, if you have one.

1981 was a transition year, the transmission may be completely vacuum controlled.
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  #4  
Old 04-03-2011, 01:11 PM
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Thanks...Instead of playing with the modulator, could I just disconnect the line from the engine and plug the ends? Wouldn't that be the equivalent of setting the modulator to the "hardest" shifting position? I read that the vacuum softens the shifts.
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  #5  
Old 04-03-2011, 02:02 PM
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Here's the 116 722.1 transmission with 300k or so miles on it. Its history is unclear, and the donor car has been scrapped:


Here is a closeup of the part number:
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Old 04-03-2011, 02:11 PM
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I've asked a similar question in this thread:-

Just dreaming - 300D automatic gearbox replacements?

The top picture you posted looks like it is the same as my NON-turbo 1981 300D 722.118 transmission

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Old 04-03-2011, 02:33 PM
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The only difference is probably that the part number starts with "123" and mine starts with "116". They are both 722.1 models ... are they the same, or interchangeable? that is the $1 million dollar question.
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Old 04-03-2011, 02:58 PM
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Here's a post that seems relevant, too. I posted part numbers and photos of my transmissions in post #15.

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