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For all versions of the Ultramatic, the factory originally called for Type A automatic transmission fluid (ATF). An improved version of fluid was later announced (see SC Vol. 29, No. 8) for the Twin Ultramatic, AQ-ATF - also known as Type A, Suffix A. However, neither of those formulations is available today.

In the beginning, there was no fluid specification for any automatic transmission other than Type A, but as mechanical technologies evolved, so did fluids. By the 1960s, Ford had developed Type F to replace Type A for its transmissions. GM continued to specify AQ-ATF, until the late 1960s, when it introduced Dexron. However, Type A, AQ-ATF, and the original Dexron formulation could no longer be produced when whale oil, used as a friction modifier, was eliminated in the 1970s, due to a moratorium on whale hunting. During the 1980s, Ford migrated to Mercon, which was essentially the same as Dexron II. The evolution of ATF types gets progressively more confusing as time goes by, as a succession of synthetics blends began to emerge in the late 1990s.

Getting back to Ultramatics, my father, who went on to a GM store after working as a mechanic in a Packard dealership, had once told me to use Dexron in place of Type A. Recent online explorations affirm that Dexron is backwardly-compatible to AQ-ATF and Type A.

However, after a complete drain and refill (including the converter) with Dexron II in my '56 Patrician, I noticed a moan from the Direct Drive clutch (when engaged) under light throttle. I worried that a full tear down and clutch replacement was needed, but before I ever got to that point, similar complaints from others who had tried Dexron revealed that refilling with Type F often provided relief.

In the absence of other hydraulic/mechanical issues, ongoing discussion, here, continues to favor the use of Type F in units that have original equipment or factory-approved replacement clutches and bands.

Supplier data describes Type F as a high static friction fluid that allows the shifting clutches to lock up or engage quickly. Put simply, Type F is "more sticky" than Type A, while Dexron is "more slippery". Friction modifiers used in Dexron offer a smoother shift, but that suggests increased clutch slippage, which might lead to faster wear of the linings.

On the other hand, one has to wonder if the Dexron formulation might be more appropriate for those units which have been rebuilt using modern, GM-type, friction materials. Kanter Auto seems to indicate that it is NOT required with their kits:

https://packardinfo.com/xoops/html/modules/newbb/viewtopic.php?topic_id=2812&forum=4&post_id=29244#forumpost29244

We've not heard from other suppliers (yet).

Although I haven't checked on the availability of Type F, locally, I found web pages featuring the product from major suppliers, like Mobil, Pennzoil and Castrol. Type F also seems to come up online discussions in agricultural circles. However, I've since read that Type FA will replace Type F.

Meanwhile, some owners - following a tip from member Turbopackman - have reported improved performance with their Ultramatic by using B&M Trick Shift fluid, which I've heard is essentially Type F with dye and a friction-modifying additive.

In conclusion, both Dexron and Type F appear to be acceptable alternatives for the Ultramatic; the choice depends on how your transmission is built and performs.