Currently using Mobil 1 synthetic 75w90 in the transmission. What difference if any would be seen using the 75w140. No gripes with the 75w90 but open to improvement.

Well gear oil does smell but you get used to it. It's a vehicle after all.

 

I chose the Royal Purple 75 140 because the heat here is unbearable for the tranny.

 

Minor noticeable difference between the two. The 75-140 would be a little better during the hot summers.

 

on the bottle of 20-50 mobil 1 V twin it says it's for transmissions - looks to me it says it's good for all three holes?

 

I'd just stick with the 75 - 140 all year round and change every 10K.

 

Clint, Are you using Mobil 1?

 

I prefer the lighter 75/90 in the fall and winter, definitely the 75/140 in the summer. The 140 is like molasses at cooler temps. Probably won't matter, but I switch Mine. Got 36k and no issues...

 

My dealer said to use one the Belray products in my transmission.
I did..... 12FLHX.

 

I bet you would not notice any difference.

 

I have used, 75-140, Amsoil 20w50, Syn 3, Formula Plus, and Mobil 1 75-140 and i really haven't seen any difference....