1986 500sel transmission prob

I have a 1986 500sel AMG that is shifting terrible. It will only shift if RPM's are high, over 3000 and you let off accelerator.
Fluid is OK. I checked the modulator valve with a vacuum pump to make sure
it would hold a vacuum and it does. the vacuum gauge on pump (with engine idling) showed the vacuum to be in range. The filter has been replaced also.
Bad modulator valve??? Any ideas??? It just started doing this suddenly. We don't drive this car very much either.
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The modulator controls the relative softness (or harshness) of shifts - not WHEN shifts occur. (More vacuum to the modulator makes shifts softer.)
The transmission is "told" the engine's throttle position. I don't know how this is done on your model, older diesels have a rod or cable from the throttle linkage down to the right side of the transmission. I understand other models use vacuum to accomplish the same and suggest your car may be one of these. A broken or leaking vacuum line would be the suspect if that's so.
Others may have more specific suggestions on this subject.
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Well, mine is a gasoline engine, not deisel. Thanks.

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I was going to say you do have throttle pressure control but......
You say you have a 1986 500SEL??? In the USA, 1985 was the LAST year of the 380/500 series. 1986 was the first year of the 420/560 series.
What exactly do you have??

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It is a grey market euro car. 500 sel with AMG package.

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Look at the right rear corner, down at the in-board side of the valve cover. Below the black hose sticking out and going to the air cleaner. Do you see a round silver rod coming up from the transmission? It has 2 sliding tabs on it. The sliding tabs are part of the piece that snaps into the gold colored bushing. Is it snapped in place?

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it's late here in georgia, I'll check that out tomorrow. thanks.

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Check the "Kick Down Switch" under the accelerator peddel. They are known to stick and cause this problem. Paul

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no. it isn't stuck. is it possible that is bad? would it be same symptoms? thanks

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none of that stuff. It does have a cable on that side from accelerator setup on engine to the transmission. cable is connected and not broken.

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jb,
How many miles the trans has? Hate to say this but maybe it is time to overhaul it. My 560 was shifting very rough and sometimes did not want to shift. It turned out it had worn internal components. I overhauled it.
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180K. I know that is a lot, but it was working perfectly until I took it to a garage to have a leaking seal replaced. Been bad since I got it back.

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