Re: Twin Ultramatic fluid?

Posted by Owen_Dyneto On 2022/8/18 12:52:08

I'd wait for a reply from Ross Miller and rely heavily on his advice, he's the authority on Ultramatics.

But IMO full synthetic would be a rather poor choice. Ultramatics, Twin or otherwise, were designed around the fluid of the day, Type A. The closest we have today is Type F, followed by FA. These fluids are characterized by a "grippiness" (or lack of slipperiness) to promote quick engagements and firm shifts; the more modern type fluids use friction modifiers to give more slip to the engagement, a feature not desired in an Ultramatic. This is the reason that older, worn Ultramatics often benefit from use of Trick Shift, a fluid with additives to make it more "sticky" and resultant shifts more firm.

If your transmission was rebuilt using modern friction surfaces as used in today's transmissions, then conventional Dexron should be satisfactory, though it still wouldn't be my choice.