What GEAR OIL to use ? ? ? ?

ersatz

ersatz

Senior Member
I've got a 1946 Flathead V8 Ford 1/2 ton pickup truck with a toploading 3 speed and think I might be using the wrong weight gear oil in the transmission & rear axle. I currently am using Royal Purple 85-140 SAE gear oil.

However, I ran across some information suggesting 600W oil was originally required to be used in the Differential, Transmission & Steering of cars & trucks from 1932-1948. The 600W is the equivalent to 240 or 250 SAE.

I am retired and use my truck mostly as a daily driver around town(weather permitting) and store it in a heated garage in the winter.

Should I be continue using the Royal Purple, or change to the 600W gear oil? Who is using what out there? ? Looking forward to your input and thanks! ! !
 
I use old gas station common gear oil think its 85-140 been in the ****** and rear end for 20 yrs now with ocational adding to top off [cant remember the last time i did that. No troubles in all that time and its used almost daily 12 mths a yr.Leave well enough alone. Dont go looking for trouble. ken ct.
 
Use Amsoil gear lube. The modern gear lubes dissolve the copper component of brass fittings found in older standard transmissions..
 
Ken........you're probably right! Sometimes you create problems instead of correcting them. I also heard that some of the gear lubes are not compatible with certain trannys. I'll have to check on the Amsoil product as well. Thanks for your input guys!
 
In 41 Ford did not recommend 600W. The Ford Service Bulletin MA-5000 dated June 6,1941 for the regular truck recommends 90 summer 140 winter and 90 all weathers in the steering gear. If your not having a problem why change. the 85-140 is what I have been using. Synthetic lubes do not seem to stay put, you may develop more leaks. Although they are fine for modern sealed engines and trans. I would definitely NOT use synthetic in the rear wheel bearings.
 
600W steam cylinder oil was pretty much obsolete by the mid 30s.

I've had troubles keeping some synthetic oils from leaking through older type seals. Straight grade gear lubes meeting the old GL1 specs are near impossible to find now. Lubriplate has some fomulations that are compatible but you can probably get by with modern 85/W140 weight GL5 types. They don't put much sulphur in there anymore. That was the additive that was destructive to yellow metals back in the 40s & 50s.
 
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