87 MB 300TD shifts rough

My son loves his old wagon and has quite a bit of money invested in it over time. Now it is shifting rough especially on cool mornings. He has had the tran fluid and filter changed but without improvement to the problem. If we have to replace the transmission, it might be the straw that breaks this camel’s back. What do we do?

As I understand it those trannys can be cranky. One thing to check is that each and every vacuum hose and fitting is in good shape. You might also post this on an MB site, lots of folks keep those things running (forever, it seems!).

Automatic transmission, I assume. It seems likely that if your son has been to a mechanic with the problem and had the fluid and filter changed, the mechanic would also have looked at the vacuum modulator. On that model car (W124 chassis), the transmission is vacuum controlled, and the hardness or softness of shifts is greatly affected by the vacuum modulator being correctly adjusted. Other things will affect the shifting, too, but the modulator is the place to start checking. It’s a simple adjustment made without disturbing the transmission in any way, so no big $. Then, as texases says, have the mechanic check all major vacuum lines. Mercedes of that era don’t like vacuum leaks; too many mechanical systems are dependent on vacuum, including door locks, trunk locks, some suspension components, climate control vents, and transmissions.

Mercedes diesel guys have a ton of experience with that sort of issue. Try a M-Bz forum like either of these: