So after a recent road trip and some other driving around it appears that I am beginning to have some transmission issues. When I am accelerating in 4th gear it appears to be slipping and the transmission and engine will lug as if I was in too high a gear for the speed I am going. So it seems to me that I am going to need a replacement pretty soon. I found an 85 van near me that has a 6.9 diesel in it. The engine is blown so they are looking to get rid of the whole thing. I am thinking I can pull the trans from it but I am not sure considering that the engine is a 6.9 and my engine is a 7.3. If they are both E40Ds, would they match up? How about if the transmission is a C6? Would I be able to swap that in in place of the E40D?

My van is a 91 with a 7.3 diesel and E40D trans. The donor is an 85 with a 6.9 diesel and an unknown automatic.

 

'89 was the first year for the E4OD so your donor van will be a C6. You can swap the C6 for your E4OD but the ECU will set a transmission code instantly. And your rear gear is intended for an OD transmission.

Not to mention, it will take a lot of work to change from an E4OD to a C6. You will need a new cross member, drive shaft, linkage, flywheel and torque converter.

I would suggest you replace you E4OD with the correct E4OD. Its always a PITA to change to a different type transmission. It costs more than you plan on and it doesn't work as well.