Re: 1956 400 Ultramatic Transmission Questions

Posted by HH56 On 2021/2/25 10:14:18

Unlike the earlier Dexron fluid which was designed to allow more slip for smooth engagements in GM transmissions of the time that used a different type friction material than the cork used in Ultramatics, those who have used modern Dexron III say it seems to have additives that compromise between the old Dexron and F type fluids and will allow a satisfactory grab. It seems to work just fine in Ultras particularly if it is one has been rebuilt with bands and clutch discs which have been relined with modern materials now available from our vendors.

For years type F was the closest modern equivalent to the original 50's specification for the type A fluid Packard used. It was recommended for use with the cork linings so they had a quicker grab to better avoid slipping and possible burning. It provided a much firmer grip than the Dexron of the time. A few years ago a fluid started to be advertised by one of the old car vendors that was supposed to be the same spec as the long obsolete original type A. Fairly expensive, I don't know if it is still around or if anyone tried it in their Packard since type F seemed quite satisfactory.

Trick Shift is used by the racing crowd and is a lot like type F but has additional additives which the descriptions say conditions the lining material and changes the grab characteristics of the clutches and bands for a fast and more solid engagement. Those who have used it say it seems to help the old hardened or glazed cork direct drive clutch engagement be a bit better and quieter but is more expensive than type F. With a rebuilt trans using modern friction materials it is unclear if it makes any appreciable difference to be worth the added expense.

I don't know if or when Ross is back from his trip but he will probably have some suggestions if the throttle linkage turns out to be OK.