I have both a 1985 300TD and a 1983 300SD, both have weird shifting issues.... The 300SD just started to show off issues a few months ago (I've had it for maybe 6 months).

It seems that after I am driving and show down to a stop at an intersection, if I push too hard on the pedal, either it jerks when it shifts to 2nd, or the engine revs for a half second before it picks up into 2nd. Both situations happen about the same frequency. I am able to avoid the weird shifting if I simply accelerate slowly enough into 2nd gear. There is no other known vacuum problem - the heating ducts, ignition, brake booster, power locks, etc all work without a hitch. Also, any hard shift is usually only when it's colder or just starting out, and after a while, it disappears. I haven't changed the transmission fluid, but when I bought the car 6 months ago, it was a bright red color. I don't know what the fluid status is like right now, I'll check it in the morning.

How am I supposed to start/warm up the car in the cold (<40 deg F) before driving off? Should it sit for a few minutes idle? I used to do a trick on my older 300SD where I would hold down the accelerator pedal slightly to warm up the engine slightly for 30 seconds before letting it get down to idle - otherwise it might cut out, depending on the temp outside. I've also been told that you can cycle the glow plugs 2-3 times for 30 secs each. Is that any different than holding the engine above idle? Is there a right way vs a wrong way to start the car in the cold, and before driving it off? Is it normal for it to drive slow/rough when it's cold out for the first 10 minutes? I understand that the engines are versatile, but I don't want to inadvertently be abusing it.

I also notice a similar problem with my 300TD, but this always happens at approximately 40mph (2nd to 3rd gear?). It revs up for a good second and then finally picks up in the next gear. I just replaced the transmission fluid, and it very likely could be vacuum related. Besides hard shifting, the ignition cutoff doesn't work as expected (waits 2-3 seconds to cut out), so I'm wondering if any other vacuum item (besides the relay thingy that hooks to the side of the transmission) has something to do with shifting, air intake, etc. I did notice that there has been some oil in some of the vacuum tubes, but otherwise cleaned out the thicker vacuum tube that goes from the intake/turbo to the side of the fuel injection pump (that uses the banjo bolts).

They may be unrelated issues.

The 300SD is my daily driver, so it's more of a concern. The last 300SD I had always had hard shifting and after a year and a half, something inside the transmission broke and it got stuck into neutral/park. Am I maybe doing something wrong with how quickly I accelerate?

Thanks,
Tomas