Can anyone tell me what the difference between a 73 220D 4 speed and an early to mid 80's 240D is? Are they interchangeable? What about the rear end? Are the gear ratios the same? Thanks in advance.

I don't know the 114/115 cars that well. It's been a long time since I had a wrench on one.

I do know that in about 1980 or 1981, the 240D four speed manual transmission changed. They are interchangable if you use the mounting plate on the back of the engine that goes with the transmission.

Because of this, I expect that the early 123 240D manual would interchange, but I cannot confirm that.

I have no idea about the differentials, but there should be plenty of 114/115 differentials in the salvage yards and should not be expensive.

Good luck,