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I am wondering if anyone has changed out their rear-end and tried synthetic? I have a 1951 Patrician and getting ready to, kind of curious if anyone has done this, and any pitfalls to worry about? Thanks in advance!

What's the point? The gears will last plenty long with regular fluid.

I've thought about that too, not worried about doing it for that reason. the worst thing synthetic does is protect the parts better, and it isn't a ridiculously expensive option eihther, $18.99 2qts, why wouldn't you?

I mean, offhand I don't see any reason it wouldn't be fine. But I doubt it will make any noticeable difference either.

Pretty sure I put synthetic in mine back when I did it a few years ago. I either used 75-90W or 85-140W....can't remember and I don't think it matters either way since both cover the 90 spectrum. No problems that I can report. Seems to be doing just fine and I've put a couple thousand miles on since then.

-Kevin

Starting with I've never had a Packard rear axle apart, but I do run a transmission shop that does a fair amount of axle work. As long as there isn't brass, a GL-5 75-140 syn would work well. The synthetic seems a bit more resilient to heat and breaking down over time. Plus, it has better cold weather properties which are a moot point with most, if not all Packards in our current era. The GL-5 spec has an additive in it that will attack brass or bronze over time. A GL-4 spec gear oil is safe for brass.

Mark
Berkshire Transmissions
North Adams, Massachusetts

Thanks for the great info guys!!

I refilled my '56 differential with Amsoil 80w-90 synthetic gear lube after inspecting it. This was before the car was put back on the road, so I have no comparison. I have had no issues. I have been running synthetics in all my cars for decades.