When I did the Trans Service on my old-but-new-to-me 4R100, there was sludge in the pan.
Drilled out the pan, and brazed on a drain plug (some factory pans had 'em, some didn't). Did a few cycles of running conventional ATF, and dropping 6L at a time from the pan.
Once things started running cleaner, I switched to synthetic (Amsoil ATF).
Magnefine did enough factory testing with Ford, that dealers started installing (up here, at least) a Magnefine filter when doing 4R100 swaps. I seem to remember something about an ATF service interval extension when running Magnefines, but don't have a Ford link handy for that. I've cut one apart, and liked what I saw (intact filter, beefy magnet collecting fine metal, a decent bypass design, and a strong filter body).
Rgds, D.
Drilled out the pan, and brazed on a drain plug (some factory pans had 'em, some didn't). Did a few cycles of running conventional ATF, and dropping 6L at a time from the pan.
Once things started running cleaner, I switched to synthetic (Amsoil ATF).
Magnefine did enough factory testing with Ford, that dealers started installing (up here, at least) a Magnefine filter when doing 4R100 swaps. I seem to remember something about an ATF service interval extension when running Magnefines, but don't have a Ford link handy for that. I've cut one apart, and liked what I saw (intact filter, beefy magnet collecting fine metal, a decent bypass design, and a strong filter body).
Rgds, D.