re: 4K trans/diff fill

["Matt Martinsen" <mattmartinsen@hotmail.com>]

>GL5 is currently recommended by Audi, since its a "step above" GL4.  
>GL5 is
>also used by the military, hence the
>"Mil-Spec" equivalent.  You cant go wrong using the GL5.
>Basically you will have more protection than you will need!
>In my CGT I run 145W/90 GL5.  Why?
>The differential bearings suffer excessive wear with 90W.
>Bearings go, ring and pinion soon to follow!
>Use a 2 foot plastic tube to fill gearbox.              Mik

GL-5 for rear differential, GL-4 for transmission/center differential 
(common case)  GL-5 is not backwards compatible, it is not intended as a 
replacement for GL-4 oil.  Which is appropiate depends on the design and 
materials of the transmission.  I had an '86 Subaru once that used GL-5 
in the transmission, my '86 5KTQ uses GL-4, I think Audi still specs 
GL-4 for manual transmission in new cars.  Audi does spec GL-5 for the 
rear diff because GL-5 is better in high pressure, hypoid applications, 
the additives that make this possible also make it more corrosive to 
things like soft-metal synchros, not the stuff you want in a manual 
transmission (unless the manufacturer designed it this way, alternative 
synchro material, etc.)  It's not a matter of "better," it's what is 
appropiate for the application.  If GL-5 was a "step above" GL-4 then I 
don't think Audi (and many other makes) would spec GL-4 for their 
transmissions, especially since GL-5 isn't exactly a new specification, 
it's been around for a while.  Check with the oil manufacturers 
recommendations, most are rather explicit in not putting GL-5 in a 
spec'd GL-4 application.
-Matt Martinsen
Seattle, WA


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