Re: Differential Oil Change - How the Heck?!

Posted by Ross On 2015/10/4 6:33:50

I find the higher GL numbers too slippery for use in transmissions; they tend to make the synchros less effective.
Get some 90 weight GL-1 from NAPA or Tractor Supply.and use it for the transmission and or overdrive only. Or as you can see from the handy chart, buy some straight 40 weight engine oil and pour it in. I use either of these in my cars.

Packard stick shifts are by no means delicate flowers. There is no need for any particular wonder oil. The high GL numbers are formulated for the sliding action of hypoid gears. There are none in any Packard transmission. In fact, extra thick oils, or oils thickened by long use will not adequately lubricate the needle bearings in the countershaft and are a death blow to R9 overdrives. If you wish to be very diligent, change it once every 10,000 miles or so.