My father-in-law has a 1972 Econoline E250. Lately it has been making a humming sound from at least transmission to the rear differential. I want to help him out but not knowing Ford's all that well, especially van's I wanted to know if anyone has dealt with this in the past. He has had the differential replaced in the last 2 years. He has also changed the drive shafts u-joints in the rear drive shaft. He is wanting to change the u-joints that connect to the transmission as well as possibly the yoke. Since he is a shade tree mechanic, some of his friends have recommended putting grease in the rear diff as well as changing out his transmission fluid. He has said that there is no transmission oil pan and that in order to change the filter in the transmission, he would have to disconnect it from the engine and fill it from the dip stick tube. I have not done much research on this either but I am not sure where to start.

If I replaced the transmission, do I have to find another E250 van? Is there a truck that is compatible that I can pull the transmission from? Are the differentials compatible from trucks to vans? If so what years? Any clue what his humming sound could be? Thank you all for reading and helping.