4R100 trans trouble

[KMcCullah]

Thanks for the info Mark. Info from a guy in the biz is so good. Priceless really!
I'm going to follow your advice and leave the pump pressure alone. I would rather have a solid mechanical fix than a electronic one.
My bet is the same as yours, when the cheap rebuild was done, the VB and AccB were ignored. But it sounds like the bodies are sometimes what cause the the clutches to get burned to start with.
I'm going to start with replacing the AccB. The one I've found for a diesel comes with a diagram that shows where to drill the seperator plate and what size. $200 bucks and a few hours is a no brainer.

[FirstEliminator]

  If you haven't ordered the new one yet, you could probably fix yours a little bit cheaper by buying the tool. But when all said and done, it probably wouldn't be much cheaper. Does this diesel accumulator body have the heavier duty line pressure modulator valve?

   Let me know if you have any questions in the process.

[My427stang]

This is the kit I used on mine

http://dieselinnovations.com/techfiles/sonnax.pdf

Change the piston, called a Sonnax valve here, and then tighter accumulator springs (3 of them, tricumulator according to this)

It made a great tranny shift incredibly, highly recommend it for the cost and 20 minutes to install.  In addition, I had converter lockup programmed to hit hard, so it felt like a solid shift.  So the added pressure to the clutches should have made it last much longer and the same with the lack of slip for the TC clutch

I traded the truck in a few years later, but it was an absolute sweetheart, even with 10K on the bumper through the rockies

[KMcCullah]

Thanks for the info guys. Given the unknown history of this whole mess, it would probably be best to just get the complete rebuilt unit.
Check the link:http://www.dieselsite.com/factorytechvalvebody-theoriginalfordpowerstrokevalvebody.aspx
I guess I assume it would have the HD line pressure modulator valve. Will call and ask several questions before ordering.

[KMcCullah]

Revisited... A few weeks ago my troubles came back. Same thing was happening. No reverse and no 2-3 upshift. Since last fall, I have watched many utube videos on the 4r100. I know enough to be really dangerous now. 
So I pulled the pan, main valve body and modulating body. I was looking for the 2-3 valve to be stuck in the main VB. But all was ok. The mod body did have a stuck valve tho. This was not what I wanted to find. Everthing I had read and seen told me the mod body would not cause the problem I was having. I hauled my bodies down to a reputable local tranny guy for a show and tell. What he said was encouraging. Depending on the year of the seperator plate, a stuck valve in the mod body can cause my problems. So with this advice, I liked my odds again. I bought the Accutech mod body for the Powerstroke and put everything back together. Filled it with cheap oil. (just in case the whole thing needed to come out) And crossed my fingers. And how about that....IT WORKS! IT WORKS! What a different animal now also. The shifts are short and crisp. But not hammering, like when I was running the hot program from the Hypertech tuner.
So today, I took the banjo bolt out on the pressure side cooler line and tig welded the holes so oil won't bypass to the return side without circulating to the cooler first. (more utube wisdom) Also installed an external Balwin filter and shelled out for full synthetic oil.
Next with be a tranny temp guage. And a very light foot.......