Gah! I hate it when people say "reverse rotation" It leads to spread of misinformation and people making ill-informered decisions.
The XJ axles are hi-pinion axles, which means that the pinion gear comes in and meshes with the ring gear above the axle centerline. The rear axle is low-pinion, which means the pinion comes in below the axle centerline.
Hi-pinion axles use reverse cut gears. Reverse cut gears ONLY work in hi-pinion axles, and hi-pinion axles can only use reverse cut gears. The other option is standard cut gears. These are only for low-pinion axles.
Why standard and reverse cuts? It has to do with strength and in what directions the gears are rotating. For a particular gear cut, there is a drive side and a coast side. The gear is used in the manner is which it is strongest when the driving force coming from the pinion gear hits the drive side of the ring gear. Pretty much every rear axle I know of is low-pinion. This is because the standard cut gear (which are the only cut of gears in low-pinion axles, remember) uses the drive side of the teeth when the vehicle is moving forward.
Now when a vehicle is moving forward, the front ring gear is rotating in the opposite direction as the rear ring gear. That means if the front axle is low pinion, it is running on the coast side, which is the weaker way to run a gearset.
So what is different between standard cut and reverse cut? You change which side of the ring gear teeth is the drive side. Drive side becomes coast side, and coast side becomes drive side. Got that? So now if the front axle is high pinion, going forward, you are running on the drive side of the gears (the stronger side).
Does it make a difference? For the vast majority of people, no. The strength difference is not an issue. In fact, most often, the R&P is not the weak link in the drivetrain.
Why does it bug me when people say reverse rotation? Because every ring gear in a front axle is rotating the opposite way from the rear ring gear. You get spread on incorrect naming and you wind up with people saying really stupid things like, "You gotta run them re-verse rotatin' gears in the front axle cuz your driveshaft is spinnin' the other way."
Just remember this:
Low-pinion axle = standard cut gears
High-pinion axle = reverse cut gears
Use "cut", not "rotation"
Sorry to go off on a rant, but I like to see correct information spread and correct terminology used. It makes communicating easier.
- Eliot -
