Hey guys, 2004 FX4 here.
Starting to have issues with my transmission. Automatic, 5R55E. It clunks in gear changes every once in a while, and there's a loud groaning sound that I believe is coming from the transmission, and most recently i just found out my bell housing has a big crack in it, so I'm starting to explore my options.
I do all my own work to my vehicles, so pulling a trans in and out is no problem to me, but I'm a little daunted by doing the rebuild myself. But I also cannot afford to put more than ~$1000 into it to fix the transmission.
My local junkyard is filled with Rangers, and they only want $130 for a trans.
Would that be worth it? Even if I do put it in and its worse than mine, I believe I can return it up to 30 days, and try again.
I'm even considering getting the junkyard transmission, and rebuilding THAT transmission, so I can keep driving my truck in the mean time, and swapping it in once I rebuild with a $500 ebay rebuild kit. That way I can take my time or be able to leave it if I run into issues, and not have to get it all done in one weekend.
Why do I not see this method talked about for trans repairs, something I know we all have issues with.
Are there hidden difficulties, low success rates, or hidden issues I'm not seeing?
Any advice for those who have gone down this path before me would be super helpful.
Thank you!

 

Automatics are more complicated that engines, they have several layers of interdependent systems, so if one layer fails it cascades to the other layers, and diagnoses of the failure can not be pinpointed until its disassembled and even then unless its an obvious mechanical failure there may not be a "this is it" moment

Used automatics are a roll of the dice like all used parts, but a little more risky than a used engine because of the complicated nature of automatics

But people do it all the time, shops won't do it of course, but DIY trans swaps are popular, so go for it
Check the fluid in "new" trans, of course, and smell it, change filter and fluid if you get it
If "new" transmission's fluid "looks" new, pass on that one, had problems and previous owner changed it, could have just been maintenance but..............
A factory automatic is usually good for 250-300k miles

Check the fluid in the old trans for metal debris, if seen then flush trans cooler and lines and put in a new torque converter or you will send those metal bits into the replacement trans, not a good thing

As for rebuilding, sure, BUT.............you need to do more than just swap soft parts(clutches and bands) you also need to put in a new pump, sprags(one way clutches), OD Drum. new valve body with separator plate and gaskets is usually not that expensive and a good idea
People also like to add the "shift kits" to these transmissions

Just soft parts will pretty much get you another 12 to 18 months before there is another problem, the warranty time on most rebuilds, lol
Good rebuilt trans should be good for 200k+ miles