Hi everyone, happy to be a part of this great forum! I have paid specific attention to the shifting characteristics of my baby so I can give you an accurate description of my problems:

1) The "thudding" "clunking" downshift to first gear the I experience when coming to a stop. Funny thing is I can "baby" this sometimes and it won't do it, I have to come to a stop VERY SLOWLY. But 99% of the time I start to come to a stop and "THUD" into first gear.

2) TAKING OFF....1st. to 2nd.: Well defined, slightly harsh shift (unless I stay halfway into the accelerator, then its well defined, hardly noticeable) 2nd. to 3rd.: (same as above) 3rd. to 4th.: Slightly harsh, and not nearly as well defined as the others (regardless of accelerator position).

3) KICK DOWN.....I was told to test my kickdown switch for its proper operation (thinking it may be the culprit, I REALLY HATE DOING THIS, and I NEVER DO), so moving about 40, I engaged the kickdown, it DOES downshift, well defined, pretty harshly, I held it for a few seconds and released, the upshift was about the same, well defined, fairly harsh.

Now, I have already replaced the modulator, and adjusted, however I got sloppy shifts, and even the feeling of slipage when going too far, so I backed off things are the same, however, the mod. did correct an EXTREMELY harsh shift that used to take place when traveling at parking lot speeds. I have order the "flappers"/"levers" that are fitted to the top of the engine block as they are SHOT! I hope this helps....I am about 99% sure this is a vacuum issue, because my family used to own an '83 300SD and these symptoms (especially the "thud" into first on stops) began to happen, and were remedied by correcting it. However, that was over 10 years ago, and I don't know where to start here. ANY HELP/INSIGHT is really appreciated, thanks David.

Whenever I've had the thunking downshift it's been a result of a vacuum leak. The vacuum leak could be anywhere. In my case, it was in the climate control system and easy to check. When I shut off the climate controls, the thunk disappeared. So you could shut off the climate control, plug the door lock system leaving you with only the shut off system and transmission control system attached and see if that improved it. You could even disconnect the shut off system, plug it and isolate the transmission vacuum.
If you have a Mity Vac, you can simply check each system in turn to see where the vacuum leak is.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Thank you will definitely try that....

Forgot to mention...doorlocks not working.....

Well, tested it this morning, don't think the leak is climate control related, on or off doesn't affect it. How do you cut off the vacuum line to the locks. The fact that they do not work leads me to think the leak might be there.....is this possible....Thanks...

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2015 E250 Bluetec Black/designo Sand
2014 GLK250 Bluetec Iridium Silver/Almond
1999 E320 Sedan Bordeaux Red/ Parchment
1999 E270CDI Estate Black Opal/Black
1983 300SD Champagne/Palomino Leather
1982 300SD Silver Blue/ Pacific Blue Leather

Nope, the locks on a 300SD W126 are powered by a separate electric vacuum pump in the trunk, has nothing to do with the system for the klima, brakes, transmission etc. You probably have some cracked connectors under the hood or something leaking out vacuum, or the line to the trans or at the trans is leaking. I'd check those.

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-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

You might save yourself a lot of frustration by just ordering new rubber flex-fittings (~$10) for under the hood and replacing them. They are inexpensive, easy to replace and gives you a baseline of "known good" to work from.

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Sam

84 300SD 350K+ miles ( Blue Belle )

I appreciate all of the insight, I will definitely try these things, as you can imagine, its gets old after awhile....Thanks, David

__________________
2015 E250 Bluetec Black/designo Sand
2014 GLK250 Bluetec Iridium Silver/Almond
1999 E320 Sedan Bordeaux Red/ Parchment
1999 E270CDI Estate Black Opal/Black
1983 300SD Champagne/Palomino Leather
1982 300SD Silver Blue/ Pacific Blue Leather