Re: Lubricants - 8th Series

Posted by Tim Cole on 2021/10/22 19:09:41
Okay, I will try to blow the smoke away on this issue of mineral vs EP (extreme pressure) oil.

When Packard introduced the first Hypoid gear set the EP oil used was a lead based soap (or something like that) that was reactive with copper bronze alloys. EP oil is needed because Hypoid involves sliding action which creates boundary lubrication conditions (read metal to metal). So anything going into the differential must be gear oil (GL-5 being the current standard). 85W-140 means that when the oil gets hot it will not thin below what a cold 140 weight oil would be.

Some automakers were recommending motor oils rather than gear oils for transmissions as late as the 1970's, but that was going out the window as early as the 1950's; for example, 1952 Chevrolet was allowing EP gear oil for manual transmissions. Today the non-EP transmission oil is rated MT-1, but the Packard non-synchro trans is an all steel unit so EP is fine for it. Some people are dumping heavy stuff like EP 250 into those transmissions because they don't want to learn how to shift. Those heavy oils just serve to wear the engine out faster and rob performance. I used to bomb around in Hirsch's 745 which had like 90W EP in it and the gear whine was so loud cars would move aside thinking it was a fire engine. Billy used to drive it through NYC and the Holland tunnel in second gear. Totally awesome.

The steering gearbox has bronze it as do the chassis parts, but today's EP oils are probably okay (EP in the Bijur should work just fine, and, you may not know it but 90W gear oil is equivalent to 50W motor oil).

Why do I say all of this? Attached is the military specification for gear oils. In it is the non-corrosion specification for copper. If you read the label on these gear oils you will find reference to the MIL spec on the label. That is your assurance they are compatible with bronze parts. And besides, who knows what has been in these units over the years?

Attach file:


pdf MIL-PRF-2-2105E - Gear Oil.pdf Size: 826.63 KB; Hits: 46

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