Hello everyone, I just purchased a 1983 Mercedes 300d with 155,000 miles and am trying to resolve a transmission problem. The car is "lagging" when shifting from 2-3 and 3-4. At the same time when the car "lags", and right before shifting, not only does the car slow down a tiny bit but I can also hear the rpms go up and like a small "slipping" noise, then it shifts. This all happens in fractions of a second.

Currently I have just changed the transmission fluid (including from the converter) and the transmission filter. This did not help at all.

I am now looking at the vacuum system. Using a MityVac, the "T" connector that runs of the vacuum pump has 20hg. This seem fine according to what I had read online. Now comes the part that "could" be the problem. I connected the MityVac to the line that goes to the modulator valve. When the car is on idle, It has 15 hg. When the car is fully accelerated, it goes down to 10hg. I read somewhere online that when the car is accelerated that it should fall down to 0? Could this be the problem? If this is the problem, which part do I need to replace

Thanks everyone,

Adiel

ps: I am attaching a picture of where I connected the mightyvac which also shows the black line going to the modulator disconnected.

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