Here's what Eaton says about lubrication of the TrueTrac:
Detroit Truetrac
High quality mineral gear lubes are required for use in Detroit Truetrac differentials. Regardless of the lube type, always use a GL5 rated lube with the least amount of friction modifier. Mineral lubes lacking friction modifiers (limited-slip additives) were historically recommended for all Truetrac applications because friction modifiers can slightly reduce the bias ratio (limited-slip aggressiveness) of Truetrac differentials. However, to address the continually increasing power outputs of modern powertrains, many vehicle manufacturers have switched to synthetic lubricants as a counter measure for increased axle temperatures and prolonged service intervals. In general, consult the vehicle owner's manual for the manufacturer's recommendations for lubrication type, weight and fill volume. This will ensure lube compatibility with the seal materials and bearings used in the axle. Eaton Performance technical support is available for any concerns in lube selection.
Source: Download the PDF file under the Documents tab at
Detroit Trutrac Differential, Helical Gear Limited Slip Differential - Vehicle - Eaton
I'm using Redline Heavy ShockProof® (
https://www.redlineoil.com/product.aspx?pid=44 ) in my helical gear differential (Powertrax Grip PRO
https://www.powertrax.com/product-in...action-system/ ) with no apparent issues, though I note this from Powertrax (Richmond Gear): "
Because there are no friction plates, no friction modifier additive is necessary. Always use a 80W-90 weight petroleum based gear oil with a GL-5 (or higher) rating, friction additive/modifiers should NOT BE USED. Synthetic oils and oils containing friction modifiers are not recommended."
Good thread here on TrueTrac gear
oil:
https://bobistheoilguy.com/forums/ub...ecommendations