Originally Posted By: Jim Allen
Originally Posted By: Loobed
My thought is that the increased size would create a space for the ring gear to push the oil so that there was less oil on the gears. The metal one, on a GM, is made to direct the flow of oil back to the bearings on the side of the gear housing (or whatever it is called).
I have had discussions with axle engineers (Dana and AAM) about this and there is something to your comment. The proximity of the cover to the ring gear does direct the oil flow to an extent, both for cooling and lubrication. Certain GM covers (notably the 8.8 (12-bolt) and certain 8.25 10 bolts have a specially designed cover that directs oil flow to the carrier bearings for the reason you describe.
All that said, the Mag-Hytec cover does reduce oil temp by 15 degrees and the man that designed it claims that he counters the possibility of any lack of lube by raising the oil level in the housing a little. Yes, I raised an eyebrow too but having run two covers on two trucks for about seven years, I can say that it's all worked pretty much as Mag-Hytec claimed.
Jim & Loobed:
This is a great point lost in most discussions.
Years ago we tried out the completely clear diff covers when they became available. With the vehicle up on stands we ran the vehicles up to road speeeds so we could see what happened.
As the speed increases, there was less and less liquid in the bottom of the diff. At very high speed, there was little to no fluid in the bottom of the diff (cool diff temps, hotter would yield different results). It is all in suspension.
I believe a high capacity cover is going to possibly keep the mesh point (which is pretty high) of the ring & pinion in fluid better than a stock cover. Whether this is good or bad probably depends on your application. For durability, good. For performance at high speed, I dont know, I would think there is more drag.
When using a Mag-Hytec, I would consider using 75W90 instead of 75W140 since the cooling and capacity is better and to reduce drag and pick up some more power at the wheels.