Hi. Newbie here.
I just bought a 1988 190D with a bad trans. I knew this when I bought it. Car's in nice shape, clean, runs beautifully. I figured for $800 I'd be happy even if I had to put a trans in, which I'm prepared to do. Anyway, it shifts fine through the first three gears, but fourth is effectively non-existent. It will grab a little at slow speeds when the trans is still cold, but once everything comes up to temp it's basically like shifting into neutral. Is there anything any of you would look for before assuming it's an internal issue? I'm well aware of the various vacuum issues with the 300 series, but this appears to be a completely different setup. Thanks in advance for any input.
Richard

Yours must have the control rod for shift points. Mine was slipping at highway speeds. The transmission shop took my transmission apart and found a big step worn into a shaft, and that was allowing fluid pressure to escape. He was going to rebuild it for $1,950 total, but I opted for a used replacement. I figured better virgin and slightly worn than rebuilt with questionable hands.

One thing- the car starts out in 2nd, so you feel 2 shifts, unless you floor it from takeoff, then you are downshifting into 1st, then you will feel 3 shifts.

I'm aware of the shifting protocol, and that's not the issue. The issue is there is no fourth gear, especially once it's hot. I can shift it manually, so to speak, and hold it in third and it shifts and runs great. But as soon as I move the lever up to 4, I lose drive. I think that pretty much nails it as a fourth gear problem? Thanks for the replies.
Richard

An 88 190d 2.5 I could get 1st and 2nd but not 3rd or 4th till warmed up ,I had to ride the feeder road for 5 miles then it was ready to go.I replaced the fluid and filter twice in 4 months ,it then started acting right ,I would think the parts inside had some varnished pieces and the extra service got things cleaned up a bit.

This isn't a case of it not engaging. I'm quite sure it engages. But when it does, it slips, and the hotter the trans, the more it slips.
Richard