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Has anyone done a full synthetic fluid for the Ultramatic or is it suggested? If you have done it, does it change the performance/reliability? Or should I bother? I am looking at the long-game approach.

Have you read this post?

packardinfo.com/xoops/html/modules/newbb/viewtopic.php?topic_id=3267

I am running AMSOIL Super Shift Synthetic Racing Transmission Fluid in my 56 Clipper Deluxe. It has Ultramatic 540481 which is one of the carry over 55s. I started with this fluid with the rebuild so I have no direct comparison. It is a Type F fluid targeting minimal clutch slippage. I typically use Drive. Reverse, Low, and High all engage and shift smoothly and positively. Direct Drive engages softly and disengages easily on both acceleration and slowing. Kickdowns all work well and positively. Throttle response is very good. I have tested all six of the external pressure ports and the pressures are reasonable based on the test chart. I have had no temperature issues using only the stock oil cooler (I have a temperature gauge). The only thing I'm still looking at is the slightly low direct drive pressure when engaged at lower speeds. At highway speeds it is fine. I do not have any long distance travel to make comments on that aspect. Everything works well thus far.

Its the wear factor with these

Once bushings start to wear. Pressure goes down.

Are you using electric sending unit with the gauges

Yes, I am using electric gauges.

Thanks, doing it right now!

Amsoil is who I was looking at, picked them for motor oil too.

If you not mind.

Where did you buy them.

Link?

They are all over on Amazon.com which is where I buy most everything that is not Packard-specific.

I buy direct from AMSOIL, www.amsoil.com. You can become a Preferred Customer for $10 (6 month membership) and get a discount of $4/qt on Super Shift and free shipping on orders of $100 or more (which is easy to do). I always find it worthwhile to join every time I buy.