4 speed stuck in 2nd
 

I recently acquired a 240D with a one piece 4 speed. Haven't gotten around to troubleshooting why it doesn't shut off with the key, so I've been killing it in gear. Yesterday, I came out after work, and it was stuck in second gear. Shifted fine when I drove it to work. I got it home and disconnected the shifter rods and the shifter is free. The reverse arm is free to move, but the 1-2 and 3-4 don't move. Any ideas? The car is really not worth opening up the tranny.

fluid level?

I suspect stalling it in gear didn't help the situation.
Try rocking the car forward and backward, if the internals are jammed a little that might free it up.
From your post I understand that the shifter has been disconnected and you cannot move the linkage at the transmission.
If you haven't tried yet, get under the car and see if the actual linkage moves.
Make sure your parking brake is set, as you may disengage the gear that it's in.

I would suspect either the clutch clave or master cylinder...

As a side note however, there is a red shut off lever under the hood that you can turn the car off with. Much better than killing it with the clutch.

apparently opening the 4-speed trannies is not hard, i have several in my garage. just be sure about the symptoms before engaging in more dissasembly. mine is currently hard to shift out of reverse and i think it's a linkage problem.

I should have been a little more specific. It is a manual.

all of our responses are for a MANUAL 4 speed transmission...

if the gearbox is out of fluid *(same fluid as the automatic transmission, but no dipstick) you need to pull the fill plug, and check the level of fluid FIRST!
if it is not full, I recommend pulling the drain plug, getting all the fluid out, and replacing it with dexIII or syncromesh fluid.

we understood. although the automatic also has 4 speeds, saying "4-speed" means manual. i have one of the exact same ones up for sale on ebay at present:
Mercedes Benz 240D Getrag 4 Speed Manual Transmission 716 210 | eBay