Packard Forum Index » Post-War (1946-54)

I have a 1951 300 and I was wondering What kind of fluid to use in my rear differential?

You have a hypoid rear axle so you must use an "EP" or extreme pressure type hypoid gear oil, probably not one intended for positraction types. I suspect most of us use the same thing, SAE 85W-120 or 85W-140 EP gear oil, readily available in many brands in 5 gallon pails, your local auto parts store should be glad to get you some. I believe Packard's recommendation was for SAE 90 EP for temperatures above 0 deg. F, and that of course would be fine also.

What about using synthetic?

Dave, been doing a bit of gear oil shopping lately to service the '47 Custom. From what I have seen the "EP" rated oils are designated as "GL-5". While you can buy 5-gallon pails, most parts stores sell the gear oil in 1-quart containers. Much more convenient size. Based on recommendations from you and one other, I bought four 1-quart containers of Valvoline 85W-140 for the differential.

I am also looking at a replacement oil for the transmission and overdrive. In my owner's manual, Packard specifies 140 weight straight mineral oil for these two components and warns against using compounded or EP oils. 90 weight is specified for cold weather and hard shifting situations. My third gear syncro crunches a bit when shifting into high, and I am looking to see if I can get some relief by changing oil. One poster here recommended NAPA GL-1 90W (Part No. 65-201). He says it worked miracles on a '47 Super transmission that was crunching going into second and third. It is a mineral oil gear oil. Very difficult to find. My NAPA store does not stock it and will only sell it in 6 gallon cases because it needs to be specially ordered.

I'll let the forum readers know what I end up doing and how it worked-out.

(o{I}o)

Hi John: I find the 5 gallon pails of the EP 85W-140 most convenient for me because on the 34 just the differential and trans take over 10 pints, and the rest goes quickly enough in other friend's cars. Certainly quarts are a lot easier to "squirt" in.

Simple GL-1 mineral gear oil in SAE 140 or 160 is easy enough to find, perhaps you'd consider that for your OD, though I've used the GL-5 in my 48 Custom 8 overdrive for many moons without any issues.

I had this nagging question many years ago, as my '37 115C called for an SAE 160 in the diff. Having spent many years in fuels labs for the military & private companies, this bugged me that I couldn't find the specs for this oil. So I called SAE. They put me in touch with Janet Jedlicka, the archivist, and she found and sent me the 1929 specs for SAE 160. SAE 160 back then was a summer lube with a viscosity range of 160-170 SUS (Saybolt universal seconds) at 210 deg F. Comparing that to modern oils, it falls right into the lower range of modern SAE 90 oils. Yes, SAE has changed their Specifications. So I called The Gleason Works and spoke with Herman Stadtfeldt, the vice president for research and development. I'll try to post his letter here, but Gleason made the machines that made the hypoid gears for Packard and I figgered they'd probably know what lube is needed in these gears.

(paraphrasing:)

Dear Mr. Carlson:

Thank you for inquiring about the Packard hypoid gear. In fact, The Gleason Works is a machine tool manufacturer for gear machines. All the different Packard hypoid gear sets were manufactured on Gleason machinery. Gleason employed an army of application engineers who provided the development of the individual gear set with respect to size and ratio as a service to its machine tool customers.

The lubricants were manufactured by Shell and other mineral oil companies but were sold like original equipment under the vehicle manufacturer brand. The optimal oil specification with respect to additives and viscosity were determined by the vehicle manufacturer and mineral oil companies using test rigs where they ran the axle drives for many months. The viscosity was and still is the most important factor. The attention was paid to the right additives. Hypoid sets tend to score because of the sliding velocities. To prevent the scoring, a highly toxic "lead soup, active sulfur" type was used to enhance the scoring properties of mineral oil. Today, the use of these lubricants is prohibited by law.

The interesting thing is, that you can use any of today's off-the -shelf hypoid oils (like Castrol Hypoy C Gear Oil (SAE 80W-90) to replace the axle lubricant in your vintage car and still have a better operating axle than the early oil with the special ingredients. The specification of the average axle lubricant between the thirties and the fifties is SAE 90 (MIL-0-2105).

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Good info, thanks for taking the initiative to dig it out for us.

Thank you all for the info I found some diff fluid from LUCAS I'm going to give it a try.