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

Tiny
RUSSELL KOGER
  • MEMBER
  • 1979 MERCEDES BENZ 300SD
  • 3.0L
  • 5 CYL
  • TURBO
  • 2WD
  • AUTOMATIC
  • 193,000 MILES
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.
Wednesday, February 19th, 2014 AT 8:08 PM

3 Replies

Tiny
CADIEMAN
  • MECHANIC
  • 3,544 POSTS
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.
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Wednesday, February 19th, 2014 AT 9:49 PM
Tiny
CADIEMAN
  • MECHANIC
  • 3,544 POSTS
It should read around 20 pounds PSI.
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Wednesday, February 19th, 2014 AT 9:56 PM
Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
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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Friday, April 3rd, 2020 AT 4:37 PM

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