1980 300d shifting pattern
 

I am new to the diesel world, (had a '58 180A back awhile) having been lucky enough to purchase a pristeen '80 300d with little rust (only on the bottom of the doors) and a lovely interior.
My question, which will undoubtedly seem rather pedestrian to all you experts out there, is as follows: after having done all the obvious filter changes, and a purge, I have found the shifting pattern in "D" to be of little use and have been directly shifting using the lever. I start in "S"(which sets off in "L") that automatic shift occurs at about 24 mph, and I then shift manually into "D" at forty five or so, using the sound/stress of the engine to pick the moment (have lots of experience with standard trannys)...so, two things...am I hurting the transmission by doing this? (I know about the "kickdown" switch, which I replaced and still doesn't work) ...and further. I cannot feel the final shift into fourth gear, even when driving at 75-80 mph. I know this baby has four gears, is that final shift supposed to occur at the marks on the speedometer., 55 mph?
All info is appreciated...

Please be more specific on why "D" is of little use, I assume you mean there is a problem and it would be helpful to know what that is.

There is no issue with shifting the transmission manually.

Your 1980 probably has a 722.118 transmission, which lacks the direct input from the throttle position (via rod or Bowden cable) found on the later transmissions used in w123s. The .118 relies on vacuum more than later models for shift quality and timing.

There is no relationship between the 55 mph marking and shift point. If the trans is working correctly the shift up to 4th (selector in D) should occur well before 55.

I don't understand what shift point you mean is happening at 24 mph. If you mean 1 -> 2, that is way too late.

If the kickdown switch isn't working, it sounds like the solenoid it's connected to has an issue. I don't know much about that.

Inasmuch as the trans is likely starting in 2nd, the first shift the OP is feeling is 2>3, and the 3>4 shift is being made manually.

I should think that the phrase "of little use" indicates that the shifts in "D" occur too early for the OP's taste.

Question: what is this sorcery where you manually shift the automatic transmission? Was this a thing in pre-90s cars? I desperately want to try it now. You start in S, then go to L at the right revs, and then D for 3rd and 4th? Also curious about damage. Driven quite a few standards and know the shift points in my sedan by hearing.

Yes, perfectly normal for it to start in second gear. If you want to or need to start in first gear then you'll either need to shift down to L or have a functioning kick down switch and activate it shortly after starting off.

Sounds like you need to Check/Adjust your pressure control cable aka bowden cable

Two points:

- the OP's car probably has a .118 transmission. Those transmissions only use vacuum control. There is no Bowden cable or other direct control to the transmission from the throttle linkage, as I explained in my first answer.

- I have had two cars with .117 and .118 transmissions. Both started/start in first. I know that others say theirs do not. The 1-2 shift happens almost immediately upon takeoff.

huh! I had no idea. I thought those gears were just for towing and mountain driving (further reading adds: snow and ice). I didn't realize you could push the transmission throw the gears that way. What a newb.

Shifting manually is fine.

I am not sure I would use the same sound guideline as a gasser, to determine the shift points. The diesel puts out much more torque and I think you will find that you can shift well before the revs are peaking and get the same forward oomph.

Torque is what pushes you forward, not revolutions (this isn't a Honda LOL) and the torque peaks in the 2200-2400 rpms range, based on memory. Long time since I've seen this discussed.

Oh, that makes sense. I learned on a manual petrol car so thanks for pointing that out.

The marks on the speedo are the max speed for the gear indicated by the amount of dots. So the ones you see at 55 ... are the max speed for third gear.