[BigBlue 94]

I run a quart of redline heavy shockproof mixed with lucas HD synthetic 75w90 in all my differentials. Even the detroit AND trutrac. Though they are pre-Eaton units. The heavy shockproof really cushions the gear mesh nicely and has excellent cling properties.

 

[BigBlue 94]

Absolutely! I will be doing so when I change the oil in my NP435. I think next axle oil change in the bronco will go full strength heavy shockproof. 37s and lockers are rough on half ton axles.

Make sure to run a gear lube in all cast iron cased gear box assemblies. Synthetic vs dino juice doesnt really matter except with friction clutch based limited slips. And anything you put in the trans must be "yellow metal safe" so it doesnt damage the synchros. Aluminum and magnesium cases get ATF.