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A nice, informative commentary. Thanks for posting.

Not being expert on transmissions I can only go by the statements of the guy who rebuilt mine and the QA part of me agrees with this. He said the type of fluid used in a rebuild of older design auto transmissions should be the type that works with the type of material used in the clutches and or bands.
His feeling was that the newer materials better suited to newer fluids. Also said he felt it was better to use the same brand if fluid needs to be added. All of his comments made sense to me and if need to add fluid. Most old car owners carry a few extras with them just in case such as engine, trans, oil brake even brake fluid. I try and keep the same brand just being a little more cautious.

That's sage advice to follow, Al, provided those original types are still available.

What the PQIA chart (cited by DrewLA) doesn't clearly show is that there was only ONE type of automatic transmission fluid prior to the 1960s - Type A, which was replaced by Type A, Suffix A (AQ-ATF). It was even used by Ford - until the evolution of their transmission technology and corresponding fluid specifications begat Type F.

Of course, anyone who knows their Fords knows that they shouldn't use anything else when Type F is specified. However, I didn't feel compelled to dig into those details since this is a Packard forum.

Though Dexron was the next successor in the Type A lineage and was specifically recommended to me for the Ultramatic, there have been an undeniable number of compliants regarding noise in the Direct Drive clutch from owners who have drained and refilled their Ultramtic with Dexron II and subsequent 'specifications' thereof.

The fact is that some have reported relief from that issue by switching to Type F. Now, whether that's because that fluid is actually better-suited or merely delaying an inevitable rebuild remains to be seen, but what does an owner really have to lose by trying Type F, if Dexron doesn't satisfy?

One point that DrewLA brought up really caught my eye: that Ford's MERCON specification followed their implementation of lock-up torque converters. However, keep in mind that the details of that technology are quite a bit different than what was used in the Ultramatic.

Meanwhile, as people continue to question what fluid to use in the Ultramatic, I welcome the introduction of additional factual evidence.