Posted by Alan Bowes on January 31, 1998 at 00:14:32:
In Reply to: Gear Wear, Premature? posted by B Nasby on January 30, 1998 at 22:56:52:
Hi Bill,
You didn't specify exactly what kind of failures have been taking place, but here are a few things to consider:
When a ring and pinion set has to handle a lot of stress, setup is not only critical, but it should be done slightly differently than "standard." A PW bus puts a greater-than-average load on these gears, and mountain driving would magnify that.
It is probably a good idea to set up the static gear contact pattern slightly heavy toward the nose of the pinion gear teeth, since when under a heavy load, the contact pattern shifts back toward the rear of the pinion teeth. If you don't do this, then under heavy load, a much smaller tooth area will carry the entire load.
Another thing you can do is to carefully deburr any sharp edges of the ring and pinion teeth and shot peen the teeth. If you go to a good racing gear shop, they can deburr the teeth and shot peen the teeth to established industry specifications. This will greatly reduce the possibility of cracks developing from tiny micro-cracks and other small stress risers.
The kind of failures that your friend is experiencing really don't sound like they have anything to do with the lubricant selection. As long as he is using the correct weight of a good quality gear lube, there shouldn't be a problem. As to lubes, I'd recommend a synthetic gear lube. Some synthetic lubes are formulated for use in limited-slip differentials (if applicable), but read the fine print and check with the manufacturer to be sure.
I suppose it's possible that there may be some metallurgical problems with the gears, but I'm not in a position to make that judgement. More likely, it's the result of not setting up the gears to allow for the shifting contact pattern that results from the deflection of the differential components under heavy loading.
I'd suggest getting a good book on setting up gears for racing purposes, since racing loads, especially drag racing, are the closest analogues to the kinds of loads encountered when pushing a heavy vehicle with large-diameter tires up steep mountain roads.
Good luck,
Alan