I have an '85 380SE which has been driven seldomly for the last few years. The last time I had driven it, it seemed normal. However, now the car will only shift up to a higher gear once its at around 5000RPMs. So, when I'm driving on the highway getting up to speed 80-100Km/h I had to push it all the way up to almost the red zone (which starts at 5500rpms) before it will switch up to the next gear.

Any suggestions on what I should take a look at? I tried to check some of the vacuum lines (which seemed normal with a cursory inspection) but it would help if someone could point to the particular one/s to look at and any other possible things to check.

Thanks in advance for any suggestions.

Do a search on the linkage and in particular the bowden cable. You can adjust the shift points of the tranny via this cable. I had the opposite problem - my 380SE was shifting way too early. A few turns of the bowden adjuster (to take up slack, IIRC) improved things quite a bit. Still not perfect, but then we are talking about a 22 year old vehicle.

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08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280

I wonder why the sudden big change? Maybe the cable became separated from the linkage. I think there is also a downshift switch under the gas pedal that may become stuck.

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1985 380SE Blue/Blue - 230,000 miles
2012 Subaru Forester 5-speed
2005 Toyota Sienna
2004 Chrysler Sebring convertible
1999 Toyota Tacoma

On the downshift switch, it is my experience that when the switch gets stuck the car won't upshift at all. His is upshifting, albeit very late.

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08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280

Well, looked at the kickdown switch under the gas pedal and it appears to have been constantly engaged and stuck down. Took it out, and drove the car around and it switches gears at the normal times now but just won't switch down when you press hard on the gas. Will try to lub and clear that switch, if not it shouldn't be too hard to get a new one.

Thanks for the help.