Understanding gears (reverse rotation, lo/hi pinion)..

Ok so I need to understand this differential gear thing better. I think that in the rear axle, low pinion means standard rotation, which is stronger than reverse rotation? high pinion in the rear would mean reverse rotation then?

For the front axles is this all convers? high pinion = standard rotation, and low pinion = reverse rotation?

I ask becuase my 01 cherokee has the low front pinion - other than meaning steeper driveline angles, is this weaker?

And finally, the main reason I ask, is for when I change gearing, what do I need for my front (reverse or standard rotation)?

thanks for in advance to those wiser than myself!

kristoffers said:

Ok so I need to understand this differential gear thing better. I think that in the rear axle, low pinion means standard rotation, which is stronger than reverse rotation? high pinion in the rear would mean reverse rotation then?

For the front axles is this all convers? high pinion = standard rotation, and low pinion = reverse rotation?

I ask becuase my 01 cherokee has the low front pinion - other than meaning steeper driveline angles, is this weaker?

And finally, the main reason I ask, is for when I change gearing, what do I need for my front (reverse or standard rotation)?

thanks for in advance to those wiser than myself!

Click to expand...

Your 01 low pinion D30 is a standard rotation gear set, same as a 97-01 non-Rubi TJ. The high-pinions found in the earlier XJs use the reverse rotation sets. And HP gears tend to be stronger (in a front ax)

Low pinion is standard rotation, but the term "standard rotation" is incorrect. The terminology goes back to when most vehicles were 2-wheel, rear-wheel drive and had low pinion axles. So the way those axles were built was "standard."

When 4WD came about, the first efforts were just turning a standard axle around to face forward. This meant that when the vehicle was moving forward, the gears were rotating the opposite of the way they were designed. The problem is that this puts the load on what should be the "coast" side of the ring gear teeth. That's why it's weaker.

Rather than redesign the differential cases to be mirror image, the manufacturers flipped the cases to put the pinion above the axle centerline ("high pinion") and then designed gears that would put the load on the "load" side when operating in a front axle environment. This is what's called a "reverse rotation" axle or gear set, but the correct term should be "reverse cut" or "reverse bevel" or "reverse spiral."

Jeep used reverse cut, high pinion front axles in the XJ from 1984 through 1999. In 2000 they changed to using the same low-pinion front axle they were using in the TJ Wranglers. Is it weaker than a reverse cut differential? Yes. How much weaker? I don't know. Is it likely to be a problem for you? Not unless you get crazy and want to run huge tires.

For your axle you need standard cut gears, but any gear vendor should know what you need when you tell him the year and model of your Jeep. If they don't know, you probably shouldn't buy anything from them.

If you are in the market for gears, don't forget to check out our members and sponsors, such as Raw Brown.

Thanks for the knowledgeable reply! I'm not in the market yet (31's still), but when I go to 33's or perhaps 35's I will be.