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I had my transmission totally rebuilt with NOS parts and it now shifts beautifully. It took a lot of adjustment on the column shifter rods to get it so you could go from first to second without touching reverse and getting the dreaded grind.

After a few such events, I decided it would be a good idea (given the occasional grinding and all the new gears and parts) to drain and replace the tranny fluid after a few hundred miles.

The person who rebuilt it for me no longer works at the transmission shop and I can't get hold of him to find out what gear oil he used in it. The manual says straight SAE 140. so I used StaLube API/GL-4 SAE 140Hypoid gear oil.

Would I be better off running 85W90 gear oil particularly now that winter is coming on? Temps where I live will range between 30-50 degrees.

Also, I don't think the differential oil has been checked or replaced in at least 10 years. What should I put in there and would it make sense to flush out with kerosene first?

THanks!!

Though I don't drive either Packard much in the winter I use SAE85W-140 EP gear oil year-round in my manual transmission, rear axles and steering gear boxes. If you intend to drive much at those lower temperatures you noted, I'd switch to the lower viscosity, or the multi-vis.

Thanks, Owen!

I haven't been able to find 85W-140 in a GL-4 formula (which I understand is critical for the yellow metals in the synchros). I've only seen GL-5.

What would the difference be with 85W90 over the straight 140 I have in it now?

I've been using this in my rear end, transmission, steering and overdrive with no issues at all. Going on 2 years now.

valvoline.com/our-products/grease-gear-oil/high-performance-gear-oil

I believe that GL-5 formulations have been safe for yellow metals for many years now.

The incompatibility between yellow metals and multi-vis EP gear oils was probably true enough with the gear oils of many (perhaps 40 or 50) years ago, no longer an issue. So unless you've got some very old product, no need for concern; if in doubt read the label - the incompatible EP additives were based on a sulfo/chloro/lead additive sometimes called "SCL".

Important to remember that the gear oil for the differential, regardless of viscosity range, MUST be an EP (or "extreme pressure") or hypoid gear oil, not just a simple multi-vis (or not) gear oil. Though an EP gear oil isn't called for in the transmission or steering gear box, using one in those applications is a non-issue. Like Chad I've been using Valvoline SAE85W-140 for decades with no issues.

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