urS4 trans additive?

[Brett Dikeman]

On Oct 18, 2006, at 7:14 PM, John Cody Forbes wrote:

> Brett Dikeman wrote:
>> Almost....any GL4 compatible synthetic gear oil.  Some GL5 gear oils
>> had an additive that was not compatible with brass syncros and they
>> would be destroyed in short order.  I think most manufacturers have
>> stopped using said additive, but I don't know for sure, and god knows
>> what's sitting on the shelf at Shady Supply.
>
> I was going to use GL5 compatible Mobil 1 75w90, any input there?  
> Thats also what I put in the rear diff since we didn't have an  
> straight 90 weight.

I think years ago M1 synthetic gear oil wasn't GL4 'safe'.  A google  
search resulted in this hit:

http://www.mobil.com/USA-English/Lubes/PDS/ 
GLXXENPVLMOMobil1_Synthetic_Gear_Lubricant_LS_75W-90.asp

"Mobil 1 Synthetic Gear Lubricant LS 75W-90 can also be used in rear  
axles where API Service GL-4 lubricant is recommended"  Note they say  
"rear axle", not "transmission"; are there any brass bits in a rear  
differential?  I wouldn't think so...

Another hit:  http://www.se-r.net/transaxle_clutch/redline.html   
"Several prefer Mobil 1 synthetic, BUT Mobil does NOT recommend it in  
a transmission that requires GL-4.  Go here for more info."  The  
"more info" link is dead.  Who knows how old that page is...

A different google search turned up this:

http://www.mobil.com/USA-English/Lubes/PDS/ 
NAXXENCVLMOMobil_Delvac_Synthetic_Transmission_Fluid_50.asp

"Mobil Delvac Synthetic Transmission Fluid 50 meets the API service  
MT-1 EP gear oil service classification and is suitable for  
transmissions and gear cases where API Service GL-1 through GL-4 gear  
protection is required."

Wrong grade, though...that's 50w oil, not 75w90.

I'd call their number (800-MOBIL25) and ask them for the appropriate  
product for a VW/Audi transmission with torsen differential where  
75w90 is recommended from the factory...see what they recommend  
'independently'. If the Bentley lists any acceptable standards, might  
help to have those handy.

Let us know what you find...might make for a good knowledge-base entry.

Brett