Rarely can the vehicle be started when transmission is in first gear

1979 MERCEDES BENZ 300SD
193,000 MILES • 3.0L • 5 CYL • TURBO • 2WD • AUTOMATIC
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RUSSELL KOGER
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Transmission shifts good 2-4.maybe every 20-50 times the transmission will start in first gear. When this occurs shifting through all 4 gears is good. I believe this is vacuum/adjustment problem. There is a repair check/test on vacuum system but, can't find?
Help,
Russ

PS: I have seen a method of vacuum check and adjustment many months ago but can't find. I will be using a Mercedes Benz tech (dealer) who does not know details of 4 bolt units.
Feb 19, 2014 at 8:08 PM
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CADIEMAN
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you will see a vacuum hose at the rear of the transmission going to a round shift modulator you will need to remove it and check the vacuum with a gauge.
Feb 19, 2014 at 9:49 PM
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CADIEMAN
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It should read around 20 pounds PSI.
Feb 19, 2014 at 9:56 PM
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KASEKENNY
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You are correct that this is most likely vacuum related however, I suspect the modulator is the issue. I have attached a TSB that addresses this directly and then a second TSB that may be related as well. The other TSB addresses the governor as when the vent holes are plugged it will cause the issue you are seeing.

Please run through these TSBs and let me know if there are questions. Thanks
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Apr 3, 2020 at 4:37 PM