From: pwiegman@ix.netcom.com (Paul Wiegman)
What's the story here ? Are the lubs in the two that different, and
why. What happens if the same is used in both ?
The diff is perfectly happy with standard modern hypoid gear lube.
The trans is something of a debate. Original TR2-3 era factory specs
were for SAE 30 engine oil (SAE 50 for average temps above 70 deg. f.,
SAE 20 and 10 for cold and very cold climates - get a reprint of the
factory manual if you don't have one..)
Sometime in the TR4 era they switched to recommending gear oil for
basically the same transmission. The SAE viscosity ratings of engine
oil and gear oil are completely different, so you cannot compare the
numbers - but SAE85-90 gear oil is not unlike SAE30 engine oil in
viscosity, so they weren't actually changing the viscosity
recommendation that much.
Some people thus put gear oil in TR3 boxes. This likely provides
slightly better lubrication for the gears than engine oil. However, it
may be tricky for two reasons. (Some) modern GL5-rated gear oils have
additives (generally sulpher-based EP additives) which will attack
certain brass alloys, and may eventually damage the brass bushings and
synchros in an older box. Also, modern hypoid gear oils with lubricity
additives are incompatable with the cone clutch in a Laycock
overdrive, if you have one.
My personal opinion is that you would do fine running either the
proper engine oil or light-duty GL4 gear oil in a non-overdrive
box. I'd stick with engine oil in an O/D box, just because it would
never occur to the manufacturers of modern gear oil to worry about
laycock overdrives. If you happen to be able to get the "classic
forumlation" gear oils made by Penrite or Castrol, they might work
well.
I've used Valvoline Racing (engine) oil (SAE30 spring/fall, SAE50
summer) in TR3 boxes for many years with good results.
-john
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