75w-140 in a Dana 30
Super Moderator
Joined: Jan 2014
Posts: 2,109
Likes: 465
From: SE Pa. W. Chester County
If memory is good, 75x-140 is what the manual calls for when Towing.. in the Rear.. Go with what the owners' manual specifies; the engineers have a reason for that specification.
JK Enthusiast
Joined: Mar 2015
Posts: 137
Likes: 3
From: NW, IL
The manual say 75-90 as the front diff usually sees less severe operation compared to the rear. Both have the same low temperature viscosity. The 140 stays thicker as the temperature rises that is why they recommend it for towing.
