I searched the word "transmission" for this section and went through all relevant title 17 pages worth of results.

I bought the 1990 F250 4x4 reg cab E4OD truck with a bad tranny, the said it just needed the front seal and bushing, however when I drained the fluid it came out black as tar, so I found a used transmission in a still running and driving truck.

The donor truck I got has a working transmission, got it for cheap because the body is beat to hell and the tires are literally falling apart im surprised they hold air at all. This truck also has an auxilary tranny cooler in addition to the radiator tranny cooler, so I will be adding that to my truck.

So far I have found that I should replace the front main seal on the used transmission I am installing and NOT use the OEM gray type? I want to use a blue or black one?

Also I will be installing a temp gauge, as I see that is often recommended.

I will have drained all the fluid from removing the pan and pulling the torque coverter drain plug, so that should be sufficient for a flush, I will also blow some shop air through the cooler to clean anything out of the lines.

Anyone have any other advice for me?

 

I would rig up a pump or something similar to run solvent through the factory cooler and lines. Air is not going to knock loose the build up from the old "tar" fluid that was in there.

 

I was thinking the same thing today. I will prolly start off by blowing some air through it, and then I will run some cheap walmart ATF through it and see if I can get it to start flowing clean. (Not sure if solvent would be ok to use... dont want something that could leave behind a residue that would hurt the future fluid that goes in it, what is ok to use that you know from experience wouldnt cause an issue.)

The truck with the crappy burnt fluid only uses the raidator to cool the tranny fluid.

The donor truck is the one that has the extra aux tranny cooler, so all i need to get cleaned out is the lines and tranny cooler thats inside the radiator.

 

The secondary cooler on my truck is factory. With this setup, I believe you can blow out the cooler all on its own. Disconnect the line between the radiator and the secondary cooler, and undo the hose that is in-line with the return to the tranny. The line at the TOP of the radiator is the line coming FROM the tranny. The line at the BOTTOM of the radiator is the line going TO the secondary cooler. See this diagram: