5. Running on the coast side. Why? Because we have no choice. No gear manufacturers in America have a machine set up to cut them the other way. Can it be done? Possibly, but the cost of building the machine couldn't be offset with enough volume just supplying the offroad community. Can it be done overseas? Probably, but then you have a lesser quality gear set and most of the increased cost.
6. Are all high pinion rears running on the coast side of the gears? Yes. Is running on the coast side weaker? Sure. Can it be overcome? Yes. Why is it weaker, the teeth are the same size? There has been reference to the concave/convex shape of the teeth but when the ring gear is convex the pinion is concave and vice versa plus this curve in most Ford 9" and Dana 60 ring gear teeth is pretty slight. So the answer lies in the fact that the drive sides of the teeth are at close to a 90 degree angle to the direction they're pushing which doesn't create most of the ring and pinion horizontal separation forces associated with running on the coast side. What happens when the ring and pinion separate is the teeth run tip to tip instead of center of tooth to center of tooth. Can we control these separation forces? Sure. Just think of holding the pinion head on both ends of it with a 3rd bearing compared to holding it with just 2 bearings when these separation forces are at work. Now try to control the ring gear forces 3 inches away from where they are occuring instead of with a thrustblock like heavy duty rearends use including the monster trucks you see jumping and landing throttled up. I've had monster truck 3rd members in my shop and believe me they have a thrustbolt. People have called me with busted high pinion rear Dana 60's that have two distinct wear patterns on the teeth, one where they normally run and one where they run when they are under a load which is at the tooth tips where there is less material. The thrustblock in our differential virtually eliminates this ring gear deflection. Add that to the fact that a Dana 60 starts out with either less tooth thickness or less overall tooth contact and which do you think is going to break first?