Does anyone know if a W123 240D 4 speed manual is the same as a W123 280E?
 

All, as the subject says? I have a bearing noise in 1st gear and am wondering if the W123 230D trans is a suitable swap.

Thanks

Iron case, or aluminum case?

Good question, one is a 77 (D) the other is an 80 (G).

I believe that the flange for all the diesels and 6 cylinders from the mid 60’s to 1985 are the same. So I believe you could bolt the transmission on, but the gear ratios are likely different for 1st, 2nd and 3rd.

If the '77 240D trans is the donor, then it is a bolt-up to the engine. If it is replacing an aluminum case box then the shift linkage from the '77 will need to be used also. The cross-member & mount from the '77 may be required. Driveshaft length should be the same.
The internal ratios are close enough that the differences will not be felt.