Packard Forum Index » V-8 (1955-56)

I see that Dexron or Type F is generally recommended.

Is ATF+4 compatible? It's apparently a newer synthetic fluid used by modern Chryslers with superior characteristics regarding temperature stability and longevity, and is supposedly a Dexron type of fluid with friction modifiers that improve shifting characteristics, the latter having been a traditional weak point of TU?

I can't comment on the suitability of ATF+4, but keep in mind Ultramatic was designed to use a fluid without slip agents. Yes, fluids with slip agents give smoother shifts because, well, they allow some slippage of the friction surfaces during engagement. If I had a nice freshly rebuilt Ultramatic or Twin Ultramatic with new friction surfaces, proper hydraulic pressures and the like I don't think it matters much whether you use one with slip agents like Dexron, or one without. If my Ultramatic were well along in it's life cycle and the direct drive clutch were beginning to groan or "moo" on lock-up, I'd be inclined to try a fluid with "grip" instead of "slip" agents, for example B&M Trick Shift.