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Using SAE 40 motor oil is certainly one of the choices. SAE50 motor oil is about the same intrinsic viscosity as simple SAE 90 gear oil so either of them are also good choices. My Marfak (Texaco) lube chart recommends SAE 80/90 extreme pressure gear oil for the trans and OD. I believe the early concerns about the EP gear oils were that they contained sulfo-chloro-lead antiwear compounds that could attack brass and bronze components but I'm lead to believe those type of anti wear additives were superceeded decades ago; that's heresay, I don't know it for a fact but I've used GL-5 SAE85/140 is transmissions, overdrives, rear axles and steering gear boxes of 21st and 23nd series cars for decades and never had an issue.

Does anyone know for sure - are there any brass or bronze or copper components in an R9 or Rll overdrive that are wetted by the lubricant? If the answer is yes, then IMO the safest choice would be SAE 40 or 50 motor oil or SAE 80 or 90 GL-1 gear oil.

UPDATE for the curious, kinematic viscosites in centistokes:

SAE 40 Motor oil, 150 @ 40 deg. C, 14 @ 100 deg. C.
SAE 50 Motor oil, 200 @ 40 deg. C, 16 @ 100 deg. C.
SAE 90 gear oil, 200 @ 40 deg. C, 16 @ 100 deg. C.

Data from Skinned Knuckles.

Think I will go with the SAE 80/90 gear oil in the trans and overdrive Thanks Owen

I use 10-40 oil and 90 weight gear oil in trans, OD and differential in my 2 22nd series.

Thanks 666 - I was wondering if I should use a multi weight engine or stick to 30 weight - Are you satisfied with the 10-40 ?

I use the 15W-40 engine oil sold by the Indiana region of the CCCA in all my Packards. The 85W-140 GL5 gear oil in the transmissions and differentials. No worries for my '37 Six, '47 Custom Clipper (w/OD) and '55 Clipper Super (w/o OD).

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I am having my 48 serviced today. Should the transmission and overdrive units be drained and filled separately or from the same drain plug. I believe the lube chart calls for 2 pints in the trans and 1 1/4 pints in the overdrive Thanks

John, they should be drained and refilled separately. They each have their own drain and level plugs.

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Thanks JW -

Well - I had all my oils changed in the 48. Engine, trans, overdrive, and differential Not very happy about the price Midas charged , but at least it's done. Also had them install a new brake light switch. Maybe now I can continue with that problem.

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I'm more surprised Midas didn't roll down the door and stick a closed sign up when they saw a Packard coming. Even more surprised they would agree to do the work. Most of the chain shops here want little to nothing to do with anything that is not fairly common or reasonably modern.