Allen:

Those dots on the speedo are maximun rpm (redline) indicators. Going any faster will overspeed the engine (usually causing a catastrophic failure, like a broken rod). The only way to get the tranny to shift that late is to use the shift lever -- the transmission on it's own shifts earlier. You have to floor the accelerator to get this car to go -- it starts in second gear otherwise. Heavy foot is highly advised for acceleration.

I don't know if the '78 has a vacuum modulator -- you also have a control cable from the accelerator and an electric kickdown switch on the floor under the gas pedal. If the kickdown switch isn't working, the wire is broken, or the solenoid bad (of fuse blown), the tranny upshifts fairly early. W123 chassis has a vacuum modulator, W115 do not (and I think a 78 is a W123).

If you cannot feel the shifts, change the fluid pronto -- I fear that the transmission is toast from overheating and/or clutch failure. These do shift rather smoothly for the most part, but if you don't get at least a sensation of shifting at full throttle with manual shifts, the clutches are going. Check for metal shavings in the pan when you change the tanny filter -- metal shavings of any kind and more that a teaspoon or two of black powder indicates serious clutch wear.

A 78 300D isn't ever going to be a road rocket -- it will keep up if you push it hard, but you are going to lose the stoplight drags every time, so give up and take it easier -- the car will last longer that way!

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!