kittyandgary

Going to change the gear lubricant in the differential of my '03 SL55 AMG with 48K miles on it.

Is fully synthetic gear lubricant 75W140 (or 75W90) that is API GL-5, API MT-1 spec OK?

Thanks for any input.

Gary-

HFELIU

I know fully Synthetic does come in both options of 75w140 or 75w90. the difference will be that one will be thicker then the other (75w140 is thicker at operating temps) which would be great for lubing the differential, but you'll lose some Torque and a mile or two in MPG. The manual calls for 85w90. I'm using 80w90 (conventional) and because the fluid was just changed the vehicle moves nicely and I can feel a bit of extra power again. Personally I'd suggest sticking with the 75w90 as it's closer to the factory recommendation, and any well known brand will meet API GL-5 or API MT-1 specs. I use valvoline High performance gear oil which meets all those standards. Hope that helps