Posted by Gordon Maney on Sunday, May 11, 2003 at 10:58PM :
In Reply to: Front Axle Lubricant Question posted by dave horvath on Sunday, May 11, 2003 at 4:54PM :
I could not speculate as to the reason for the change. The Dana 70's with the Trachta joints specify a gear lube, not a grease, just as what you call a later PW axle. It was someone's idea of an improvement.
Perhaps the thought was that part motion in a grease created a channel or void in the grease, and it would not flow back, so to speak, whereas a liquid would flow back. Going with the SAE 140 spec. you reference, it would not take a very low temperature to get below the pour point, and then you effectively have a grease anyway.
Given any truck fitted with grease fittings permitting the use of grease.... I would use grease. Most chassis grease is oil soluble, so if you mixed grease an gear lube, you will have a somewhat dissolved grease. It would not be a problem. As far as your "why have a seal" question, you would like to avoid a situation where the differential assembly was low on lubricant due to a migration of it to the outer ends (which could be leaking....).