4R70W Low/Fluctuating Pressure

[danwheeler]

Hi All,

I have a 69 Bronco with a 96 Explorer 5.0 and 2000 4R70W controlled by the first gen baumannator. I've been using this site to search for misc info about the motor and trans for several years now but I finally have a problem with the trans that I can't figure out and am hoping the knowledgeable folks here might have some ideas.

2000 4x4 4R70W started slipping in 1st mostly when cold. It would take 10-15 seconds sometimes to engage 1st or reverse. I dont think the problem is limited to just 1st and reverse because I have had the problem in other gears just not as often. Once, on a 2 hour drive over the pass in cold weather, it would slip in OD for 2-3 seconds then go back to normal.

I have pulled the valve body and installed a Sonnax main pressure regulator valve. The shop actually installed it. They were supposed to ream it and put in the enlarged valve but they said it wasn't necessary. I was very annoyed that they didn't do what I asked but I trusted their judgment. I did this because the ATSG guide suggested blowing air into the TV/EPC port and if fluid came out the filter intlet, then the main pressure regulator valve is bad. It did. Unfortunately, I did not check it after installing the valve body with the new main pressure valve.

I also replaced the EPC solenoid and used all new valve body gaskets.

I got things back together and the problem seems to be a little better but not fixed by any means. It no longer delays going into 1st or reverse which is interesting. But it still slips when cold mostly in 1st.

I took video with the pressure gauge attached to line pressure. The readings seem really strange and all over the place.

I put some Lucas trans conditioner which seems to keep pressure from dropping down to 10PSI as often but it still slips.

here is the video:

http://www.youtube.com/watch?v=Ddyu-0l6Z-k

I'd really appreciate any ideas. I don't want to just have it rebuilt without knowing what the problem actually is. Seems like maybe a rubber seal somewhere is leaking until it gets heated up and expands?

thanks,
Dan

here is the Bronco:

[danwheeler]

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