2001 Dakota SLT 4x4 3.9L V6 basket case. Transmission is acting up.
​​​​Fluid was overfilled / foamy, replaced fluid+filter & found overdrive unit 5" wave snap ring in pieces in bottom of pan (common). Shifts & drives fine when cold. Acts up when warmed up. I'm contemplating removing the overdrive section from a junkyard '02 4.7L 4x4 (45RFE?) & swapping that if it does not have the same problem ($139, less than cost of the tools required to depress the killer spring and line everything back up on reinstall of new $5 snap ring). However I'm concerned about the rest of the transmission. Would this overdrive snap ring issue allow it to drive fine when cold but have intermittent slipping/surging problems once hot, and also cause delayed shift from first to second afterwards? I'm going to speculate that it has other additional problems in the transmission that are causing those issues. Advice? I'm a manual transmission kind of a guy, but my wife brought this thing home, bought from her coworker. Time to learn how to work on mopar automatics I suppose. Thanks in advance!

 

I put a used one in my 3.9 2wd 01 an it did fine.Be sure to replace that accumulator spring an sensors at valve body an adjust the bands. .Accumulator spring commonly breaks in these. There is a kit with all of it online .

 

Yeah I'll 2nd that, I lived with my 3.9 4x4 42RE being temperamental for 5 years not shifting 2-3 without lifting off the throttle. Funny thing is I ALWAYS thought it was the 1-2 and trouble shot it as such because putting my truck in drive it would always start in 2nd gear since I bought it. I would count the shifts and mistook the torque convertor lockup at ~42 as 4th or OD because it was so abrupt. I always read that the 3.9, esp. the 4x4 was a slug and I thought nothing of the horrible acceleration starting in 2nd as I thought it was normal. Early this year I bought a reman unit from a NC shop off eBay (find a different source IMO) and I found out what 1st gear feels like on the replacement trans while bug hunting other trans woes. After it was working I took apart my original one (which looked cleaner inside than the reman one) and found the accumulator spring split in half so I ordered a $9 replacement and filter kit for the original trans. This way when this reman one breaks I feel the original will likely work like a champ with the new spring. If you take the pan off for any reason like governor pressure etc it only take a few minutes to check the accumulator spring while your in there. Better yet just spend the <$10 and order one ahead of time and simply replace it while your in there. As hidden1 mentioned they are a common fail point.