Hi mayf.
I would choose a Group 4 base synthetic such as Mobil1, Amsoil, Red Line, Royal
Purple,
.... The other major brands (Pennzoil, Valvoline, etc.) use a Group 3 base.
See:
http://www.mobil1.com/USA-English/MotorOil/Other_Products/Gear_Lubricants.aspx
I'd use Mobil1 75W-90 because it will circulate and cool better at high speed
than 75W-140.
My '99 Ford factory shop manual specifies a change interval for the
differential
under heavy duty
usage to be 5,000 miles if petroleum lube is used and if synthetic is used it
doesn't ever need to be
changed.
Other oil's do not have the extreme EP additives (sulfur based) that hypoid
gears must have.
If your differential used spiral bevel gears, Synthetic ATF would be my choice
for a lightly
loaded application like yours.
The Group 4 base stock normally used is PAO, PAG is much better but extremely
expensive.
The Group 3 base stock is petroleum.
Bryan
DrMayf wrote:
> Time for a poll of the real racers. What, in your opinions is the best diff
> lubricant for a lightly loaded ford 9inch? Spool. What is an acceptable oil?
> Sunthetic or not?
>
> Engine oil?
>
> Auto tranny fluids?
>
> As you can see, it is going together albeit slowly. The World's Fastest
> Sunbeam (wannabe) is planning on making an appearance at WOS if the lake
> dries sufficiently...
>
>
>
> mayf
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