My dad recently found some metal in the pan of the tranny during maintenance, so he pulled it and I just finished tearing it down for a quickie inspection to see if I could rebuild it again or not. The stator support on the front pump is scarred up some, so it will get a pump. I didn't find anything else until I got to the thrust washer between the reaction and output carriers. Two tangs are broken off, the washer is almost cracked in two, and like its twin on the other side of the carrier, the tangs are all badly cracked, and pushed off center. The selective washer is perfect.
What causes this and how do I fix it? I guess the roller bearing conversion for the rear would be a start, what about the other?
I still need to tear apart the clutch packs and other gear sets, the only one I really looked at was the output carrier and it looked okay, no signs of chewed up teeth or anything.

Excessive rear endplay can let the washers get eaten alive. Use a Torrington bearing from the drum in a TH-350 along with thrust shims to replace the OEM rear thrust setup in your TH-400, it is a drop-in deal. Take a good look at the rear band and reaction carrier surface as well. They are pretty trouble-free until you start to beat on them a bit, and then the weak links are the intermediate sprag and the case where the intermediate pressure plate has a gap in the tangs on the passenger side of the case. There are aftermarket parts to reinforce this area, but generally they are not needed in a street car as long as you use a quality valve body or kit in your own valve body. Use Teflon rings on the center support and pump too for better life.

This is nuts... Found out today while looking at the case, VIN #'s match! This could possibly be the single original part left in the car!!!! I had figured the original was long gone, but its still going. Just kind of a nice surprise.