Packard Forum Index » Pre-War (1899-1942)

Go point! I have only used it to top off the 37 Packard rear end so there has been little dilution. Will be doing some routine maintenance on the 37 shortly and will drain and refill with a GL5 oil. The Penrite 250 is good for trans and rear ends with yellow metal which the Cadillacs have. I see that Penrite makes a GL5 but says no yellow metal. Does anyone know if there are brass parts in the 37 120 rear ends?
Thanks for the tip,
Rod Smith, Reno NV

Just to emphasize, it's ESSENTIAL to use an EP (extreme pressure) gear oil in a hypoid rear axle. I'm a bit surprised at Pennrite's warning about yellow metals, the very first primitive EP gear oils used an additive sometimes called "SCL" for sulfo-chloro-lead and these were indeed corrosive to brass, copper, bronze, etc. but all of the EP hypoid gear oils I'm familiar with today no longer carry that warning and haven't for many years. For many years Packard recommended SAE90 in the winter and SAE 140 in the summer; I most often use Valvoline SAE 85W-140 year-round. I also have used it for decades in Packard standard transmissions and steering gear boxes and have had no problems. With that warning, I'd avoid the Pennrite product and go with a multi-viscosity EP product from one of the major gear oil makers, Mobil, Valvoline, Lubriplate, etc.

Others please correct me if I'm wrong but I don't believe there are any yellow metal parts in a Packard differential.