Max rpm (mph) limits for each gear are marked in the speedometer -- one little orange or red mark for first, two for second, three for third.

My usual experience is that these cars, under minimal throttle, upshift fairly fast -- you should be in 4th at about 25-30 mph. This is not much more than coasting. If you have the pedal down but the kickdown switch not engaged, upshift should be around 3500 rpm in lower gears, maybe 4000 to fourth. With the kickdown switch closed, upshift should be about 5 mph slower than the max rpm mark.

This is cable controlled -- if your shifts are later than that, check the adjustment of the Bowden cable on the throttle linkage.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!