what is the usual lifespan of a 124 trans? I purchased this 93 300d at 153k (and had the trans fluid/filter changed by a reliable mechanic) and now at 156k it has a delayed shift (especially between 3 and 4) when cold. for instance, this morning it didnt shift into 4th until around 75 mph (around 4000 rpm), but then after that it shifted more normally at lower rpms.

Does it need an adjustment, or might this be the beginning of an expensive problem?

I had what sounds like the same problem. I could also get it to shift into 4th by putting it in neutral and then back in D. Once it was warmed up, it worked fine.

I very, very carefully adjusted the fluid level of the tranny by taking out about 100 ml at a time until the level was exactly right, and now it is fine.

These transmissions are VERY sensitive to fluid level.

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1991 MB 300D 2.5 Turbo (207000km) (now gone)
1993 Audi 100 CS Quattro (300000km)
1999 VW Jetta TDI (290000km)
2002 Audi A6 3.0 Quattro (150000km)
2005 MB E320 CDI (34000km)

That is normal in a 124 tranny.

Tom