My truck has an 8.8 3.55 in the rear (not limited slip) and a Dana 44 in the front.
What weight and brand do you guess recommend for each one ?

 

If cost is no object, Motorcraft synthetic from the dealer is real good, as are the RedLine oils. I use Mobil One because it is available and resonably priced. If you look at the manual, the Dana takes a different spec than the Ford axle. It is a splitting hairs type difference, something like 75W-90 in one and 80W-90 in the other. If your seals are old, synthetic may find leaks that you did'nt know you had. This did happen to me on a GM axle.

Jim

 

why are differential fluid viscocities so high?

 

Gear lubricants have high viscositys because the diferntal sees high temps and shear forces.

 

OH, okay

 

There is a different SAE viscosity scale for gear oils than motor oils. SAE 70 motor oil does not equal SAE 70 gear oil at the same temperature.

Jim

 

FWIW the absolute best mineral gear oil is the Chevron . It's early , I can't think and gear oils not my favorite topic but that stuff won new product of the year either last year or the year before. It has a Timken load rating of 70 lbs vs some other at mere 45-50 ratings .


I like Jim-n-mandy's Motorcraft synthetic 75-140 . It is made by Conoco and is a 100k lube .

For the most part leaks usually associated with synthetics in gear boxes or differentials ae viscosity related as in too thin with somewhat worn seals or older ,hardened and cracked seals .

For example , the Redline MTL is the equivelant of a 5/30 motor oil . Even the MT-90 is a 14 centistroke lube for an approximate 40wt.