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Hard shifting noise and actual thump

(1990 Mercedes-Benz 420SEL)
in Aurora, CO on March 15, 2010
what would effect my tranny shifting down from 3rd to 2nd or when I'm slowing down 2nd to 1st,is it a vacuum problem or something more serious
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on October 12, 2010
There is a small vacum hose behind the engine block and it can come off causing the problems you specify. You'll have to look behind the block using a flashlight and it's near the top. If it's off reconnecting will correct the problem. You have to get some long needle nose pliers (2) with angles to get to it and reattach.
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on July 24, 2017
More than likely you have a shift control module or the vacuum line going bad...about 200. At a transmission shop ...
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