80-90w vs 85-140w in the rear end

[JHZR2]

BMW folks swear by redline to quiet whiny rears. This is usually due to bearings, however.

Im my BMW, it quieted very slightly by changing from 75w-90 to 80w-140, not significant enough to make the change worth it.

Theoretically, the heavier lube ought to make fuel economy drop slightly. I didnt notice this in my BMW, though my driving profile changed somewhat.

Id also think that typically you'd want the smallest spread you could find. People want small spreadsin motor oil viscosity (i.e. 10w-30 instead of 0w-30), as the fluid won't shear down as much with use. Now, while a diff doesnt have as many points for shear to occut, Id imagine that the degree is MUCH higher, as you have a lot more power going through a smaller specific surface than on say, a piston in an engine.


JMH

 

[babydoggy]

conventional 85-140 becomes very thick under freezing. Pupt some in your freezer and find out. Ask them why they don't want you to use synthetic. 80-140 synthetic with a little lucas should quiet it down and give you better protection.

 

[zugdud]

Howdy folks, I have US Strange 4.56 street gears setup in an 8.5" GM rear and they have over 1,000 miles on them. They whine a bit at cruising speed and from I understand, this is normal but I have heard you can quiet it down a bit with heavier gear oil. What are the drawbacks of going to 140w? The cars service manual calls for 80-90w in the rear end...what kind of potential consquenquences could i run in to if I switched to convential 85-140w? also roughly how much parasitic loss would this create?

Also, I am using an Eaton posi carrier with the gears, eaton recommends convential lube (NON-SYN) but doesnt have any recommendations on the weight

Thanks!

[ April 23, 2005, 12:49 PM: Message edited by: zugdud ]