How hard is normal?
 

My '83 300D shifts hard and often early. Worst on 1-2 but happens 2-3. Sometimes there is a loud thunk when it hits 3rd. I took it to a Bosch certified mechanic and he said that it is shifting normal for this car. My whole body tenses up before each shift in anticipation. This can't be normal. I see lots of posts about hard shifting so I'm not sure what is normal.

And secondly, anyone in the Tampa area that is knowledgeable about these cars that would be willing to look at her? Maybe show me a thing or two about the vacuum system as this seems to be the most prevalent cause.

Thanks for any help.

if it is more than slightly firm, you have a problem. most likely the vacuum is leaking. these cars use vacuum to adjust how firm the car shifts.
do a search here for something like critical vacuum setting transmission.
use the google search.
Brian Carlton did an awesome write up and TONS AND TONS of followups make this a bookmarkable page.

Hmm, I would have sworn it was Brian Carlton... well anyway, this is the thread I was discussing...
surely there are tons more out there.
http://www.peachparts.com/shopforum/diesel-discussion/158216-its-critical-how-you-set-your-transmissions-vacuum-system-your-diesel-mbz.html

Check the vac hoses
 

THere are a few vac hoses on my W124, don't know about yours, but mine were near the air filter and near the shut off valve. Both came off because I was replacing a filter, then later the shut off valve. Even aside from those, could definitely be a vac hose.

jeff

This might help:

http://articles.mbz.org/transmission/adjust/

Unless you know that there are vacuum leaks in your system, the thing to do is T in a MityVac to the vacuum line that goes to the transmission modulator, run the line out the cowl, close and lock your hood, leaving the MityVac on the cowl where you can read it and go for a drive. Monitor your vacuum as you move through the gears at various throttle positions and see what your vacuum is doing.