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I want to  change out the transmission and differential lube.  My manual was printed in 1958.  Are there better lubricants than those recommended in this 55 year old manual?  It recommends S.A.E 50 engine oil for the Spicer 4 speed transmission and S.A.E. 140 MIL-L-2105 for the differential.  I doubt that that the differential gear lube is even a current S.A.E standard.  What's the best product for each?

The military spec MIL-L-2105 is still a good spec those specs have worked for 55 years why change the old girl may not like change lol I found out the hard way some old seals don't care for the synthetic stuff

Since I have NO LEAKS, I'm not opposed to sticking to what works - if there's nothing better.

FWIW  I changed one to SYN and could hear a hum I never had before.  Bob

Gordie -

If it ain't broke, don't fix it?

:o

Just remember that the spicer gearbox wants a non-hypoid oil while the differential wants a hypoid oil.  I use a SAE 50 synthetic transmission oil in my spicer but I'm sure it would be equally happy on normal SAE 50 engine oil.  I top up the differential with normal 85 -W140 diff oil.

Brian

The oil specified for the Spicer is actually Aviation grade mineral oil, more commonly known as "break-in oil" because it has no additives or detergents. I use it in my trans even though it leaks a bit because I happen to have some I bought for an airplane by mistake. You can find this oil at any small airport. You have to be careful with older trans because modern additives can destroy brass and other type metal bushings.

The rear uses GL-4 non-extreme pressure, most modern vehicles use XP so GL4 is not easy to find.

This link will answer your questions; http://www.mobiloil.com/USA-English/MotorOil/Car_Care/AskMobil/GL-5_and_GL-4_Gear_Oil.aspx (http://www.mobiloil.com/USA-English/MotorOil/Car_Care/AskMobil/GL-5_and_GL-4_Gear_Oil.aspx)