I managed to somehow get an old 78 300d for the free so long as I could get it running. I got it to start, and after topping off the transmission fluid it now moves...kinda. It'll shift through (I'm guessing) all three of the available gears but you have to lift off the throttle or it will slip, especially in 3rd, also if you mash the accel too much it will start slipping. I've topped off the transmission fluid, and looked for the transmission valve modulator but I can't seem to find any vacuum line running to it, do these models have vacuum running to the trans? I took a look at the vacuum diags in the stickies but I'm kind of lost as to which one would be the correct one for a 1978 300d n/a. Any help, especially with the diagram selection would be much appreciated.
Jason

There should definitely be a transmission modulator vacuum line on your car. I would search the forums here for that--particularly "vacuum" and "transmission" and see what comes up: the whole vacuum system has to be checked or lots of other things could be going wrong too (the vacuum system controls an assortment of stuff, and the rubber connectors fail, as do individual components.) Get a vacuum tester and read the posts. Make sure your vacuum system is good before you start tweaking anything else on the transmission!

Good luck. "Free" Mercedes usually get pretty expensive pretty fast...

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marshall

1982 300TD (220,000 mi.)

I'd start with trans fluid and filter change. You may notice a difference, these trans. are pretty finackey. You might also put some Trans-X in transmission before you change the fluid. Drive the car a short while then change the fluid and filter. It will remove the varnish that builds up on the internals of the trans.

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Marshall-

ahh not so fast- I disagree. Some of the early w123s did not have a modulator - or at least , not a vacuum one but a mechanical one. Anyone have a 79 300D? or is it a 78? It might matter....

Rick

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80 300SD (129k mi) 82 240D stick (193k mi)77 240D auto - stick to be (153k mi) 85 380SL (145k mi) 89 BMW 535i 82 Diesel Rabbit Pickup (374k mi) 91 Jetta IDI Diesel (155k mi) 81 VW Rabbit Convertible Diesel 70 Triumph Spitfire Mk III (63kmi)66 Triumph TR4a IRS (90k mi)67 Ford F-100 (??)

Seems like on 77's there was no tranny vacuum but a mechanical linkage. I do not know if 78's are the same way, or if they have the single vac line down to modulator on passenger side of tranny.....
Lot of help I am!

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Jimmy L.
'05 Acura TL 6MT
2001 ML430 My Spare

Gone:
'95 E300 188K "Batmobile" Texas Unfriendly Black
'85 300TD 235K "The Wagon" Texas Friendly White
'80 240D 154K "China" Scar engine installed
'81 300TD 240K "Smash"
'80 240D 230K "The Squash"
'81 240D 293K"Scar" Rear ended harder than Elton John

Ooh. Learn something new everyday! I have to get over the habit of using words like "definitely." They only get me in trouble.

One bit of advice that is almost assuredly, or probably definitely good is that any new owner of a 123 would do well to get the official MB service manual, available on CD from MB themselves (the MB "Classics" department, I believe). The CD's only cost $20, so don't spend too much time looking on EBay for them. This money is way better spent than getting a Haynes or Chilton-type manual.

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marshall

1982 300TD (220,000 mi.)

Sometime old mercedes automatics sitting around too long have their internal transmission seals dry out. Try a can of transmission conditioner and drive car very easily. It can take quite a few miles to restore those seals.
I would ask the last person that drove the car if the transmission was slipping when last in service? If not then it is almost going to be dried out seals.
Takes 1000-1500 miles sometimes with the additive to do its work. Basically the additive is a petroleum product that swells the seals.
If it turns out not to be something simple at least there are more used transmissions around for the non turbo model like yours. The automatic for those earlier non turbo models is weaker than the turbo automatic transmissions as well.
Or convert it to a five speed manual. If you locate more than one five speed manual drop me a line. I have almost given up trying to find one. You hopefully will have beginners luck and solve my problem.

The previous owner is actually an old school mate of mine; and I remember hitching a ride to school some days while he was driving it, from what he and I both remember it had a short lag before slamming into the next gear, usually feathering the throttle slightly would relieve it a little. I'm thinking it may be the internal seals since there wasn't a leak some 6 years ago and I had to add almost a gallon of fluid to get it at operating level; maybe the seals did dry out, I'll try the transx before filter change. As it is right now, the car is sitting in my backyard until I can get all the bugs fixed (minor electrical boogers and such) and somehow figure out which vacuum accessories I can delete from the vehicle. I can honestly do without the a/c/heater and other options if it means getting the drivetrain tamed in the process, after that it's getting a dual wvo setup! Thanks for all the info so far, If anybody else knows about the modulators/vacuum diagrams on this year/model please post.
Jason

The search function is your friend.

I typed in "mechanical modulator and got this as about #4 result:

1978 300D Transmission (non-vacuum) modulator adjustment

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80 300SD (129k mi) 82 240D stick (193k mi)77 240D auto - stick to be (153k mi) 85 380SL (145k mi) 89 BMW 535i 82 Diesel Rabbit Pickup (374k mi) 91 Jetta IDI Diesel (155k mi) 81 VW Rabbit Convertible Diesel 70 Triumph Spitfire Mk III (63kmi)66 Triumph TR4a IRS (90k mi)67 Ford F-100 (??)

thanks! I'm having difficulty learning all of the diesel/mercedes terminology.