the HP dana 30 has reverse cut gears where the LP dana 30 is standard cut gears
Reverse-Cut vs. Standard-Cut:
Often mistakenly referred to as "reverse rotation," the term "reverse-cut" is perhaps the single most misunterstood term by four wheelers and even many in the axle business. Areverse cut housing is not just like a standard cut housing turned upside down. It is a specially designed housing for fount driving axles. Contrary to popular belief, it does not turn backwards or in reverse. The term "reverse-cut" actually refers to the direcrtion of the spiral cut in the ring gear.
In a reverse cut axle, the spiral on the ring gear is opposite form a standard -cut ring gear. The idea behind reverse cut is to strengthen the operation of the gear when it is used for a front axle application.
In the early day of four wheel drive, the front axle used the same gears and housing as an ordinary rearend. This was done for economic reasons, since the components were already in mass production. They simply added the necessary parts to enable steering. However, all ring and pinion gears are cut in such a way that they are inherently stronger when pushing the cehicle in the forward direction and weaker when driving in reverse. That means that a standard cut (rearend style) gear, when used in the front, must push on the weaker side of the gear to move the vehicle in a forward direction.
This practive continued until the late 1970s, when Dana designed a new axle that would be stronger for front axle use and also provide better driveline angles for the shorter fornt driveshafts then being used in new trucks. The reverse cut housing and reverse cut gear set can be identified by the pinion gear, which is located abve the centerline of the axle shaft. Therefore, standard cut gears are always strongest when used in rear axles and reverse cut gears are stonger when used in front axles.
Reverse cut axles have also become popular for lifted short wheelbase vehicles like Jeeps, early Broncos and Land Cruisers. The reason is because the higher pinion location greatly reduces rear driveshaft angles. However, not all reverse cut axles are strong enough for use as a rearend. The cut of the gear that makes them stronger for the front axle use also makes them somewhat weaker for the rear axle use. The best and most popular reverse cut axle for rearend use is the Dana 60, a good choice because of its larg ring gear diameter, tooth strength, ability to accept 35 spline axle shafts and wide selection of ratios and differentials.
Two other reverse cut axle are the Dana 44 and a new Ford 8.8" reverse cut. The Dana 44 makes an excellent front axle, but just isn't strong enough for rear axle use. The Ford 8.8", reverse cut rearend (new from Currie Enterprises) has a slightly larger ring gear than the 8.5" of the Dana 44 but is not nearly as strong as the Dana 60, which has a 9.75" ring gear. The new 8.8" uses a special third member that bolts into a removable carrier Ford 9 inch housing and its somethimes mistakenly referred to as a reverse cut Ford 9 inch. Both the Dana 44 and the ford 8.8" can accept a maximum of a 30 to 31 spline axle shaft.
The bottom line is that reverse cut gears (front axle style) and axle assemblies are inherently stonger for fornt axle use because of the way the gear mesh when moving the vehicle forward direction. They also provide better driveline angles because the pinion is located above the centerline of the axle. The gear set used in each type of aaxle are not interchangeable. Standard cut gears cannot be used in place of reverse cut and vice versa. The housins are also not interchangeable. However, differental cases, be open, limited slip or locker are compatible with both styles, as long as the spline count matches the axle shaft.
-Reverse-Cut vs. Standard-Cut taken from FourWheeler January 1999
this info is taken directly from this website
http://www.cj7jeep.com/info/axle/basics.html#5
