Originally Posted by junqueyardjim

Well I think any automatic out of a W123 will work in your car if it is a working transmission. But going with that 4 speed stick is really a wonderful way to go, though it is a bit more work then just sticking in another automatic. But you must have all the parts to do the job right. Ideally you should have the donor car right there with you as you do the swap. But make a list of what you need and follow through on it. You will need everything off the donor car that makes it a 4 speed. Five speeds are so rare as to not be worth talking about. But you need from the donor car the transmission, clutch and bell housing. You will need the clutch and brake pedal assembly. You will need the clutch hydraulic parts and lines which is pretty simple. You will need the flywheel off the donor. If it is a 240D donor, it will be the light weight flywheel and it is useable on the 300D. If you are really lucky and the donor is a 300D, then you will get the heavy flywheel which is ideal. You will need the transmission crossmember from a 240D automatic. You should also use the differential from the donor, and then also the speedomometer if you want the speedometer to be correct. Then the front section of the driveline will probably need about 4 inches added to it. You should use new flywheel bolts when you re-install the flywheel, They are expensive. And while you have it apart you should have the clutch disc, pressure plate and flywheel examined, and replace and resurface as necessary. It is a lot of work and I would NOT do it on a rusty junker. But if the body is nice, it really makes a nice car, though they are just a little bit noisier inside. Mine is noisey when cold, but very comfortable as to sound level when warm. So what you should do is really check the donor car and see if everything you need is there. It is also possible that the drive shaft front section from the donor might be the correct length. Well now I see you plan to put it into a W115 which is a little different but not much. You won't be able to make a direct swap on the dash/speedometer but it will work. Is your 75 300D worth the work/effort.