Rear axles are (almost universally) high pinion.
A front axle may be "high pinion" or "low pinion," as indicated in a previously-attached post, it has to do with the relative position of the pinion centreline to the axle shaft axle - as mounted.
A "high pinion" front axle has the axis of the pinion above the axis of the halfshafts, and will therefore require a gearset with the spiral in the opposite direction.
A "low pinion" front axle has the axis of the pinion below the axis of the halfshafts, and will use hypoid gearsets with the spiral in the same direction as the rear axle.
(In the case of axles with both front and rear applications, a low pinion front is capable of using the same gearset as the rear axle would in general. Therefore, a D44LP will use the same gearset as the D44 Rear, but a D44HP may not.)
The "high pinion" axle was done for, I believe, two primary reasons:
- The increased clearance between the ground and pinion axis (generally in the range of 2-5", but that can be significant) can improve obstacle avoidance when off-road.
- Hypoid gearsets have a strong "drive" side and a weaker "coast" side (when you're backing up, you're driving your rear axle on the "coast" side of the teeth.) A high-pinion axle allows the hypoid spiral to be reversed, which means that the front axle will then be driven on the "drive" side. A low-pinion axle is driven on the "coast" side, and is therefore able to transfer noticeably less power (I think it's a difference of 7-10% - unless you're on the ragged edge of axle performance, it's probably not enough to matter.)
Earlier XJ/YJ/ZJ D30s are "high pinion," and would therefore require a "reverse spiral" gearset.
High pinion D44s and D60s can be found in some of the earlier (1960's-1970's?) Ford F150 and F250 4WD versions - for instance, I'm fairly sure that the D60HP front can be found in the late 1970's F250 "Snow Fighter" package (to accommodate the weight of carrying the snowplow, and the added strain from pushing it.)
The hypoid offest (vertical distance between the pinion shaft and halfshaft axes) typically runs in the range of 1.5-1.75", which almost puts it right at the outside of the axle tube (and therefore easy to spot.) Just make sure you're eyeballing the axle as it would be mounted - and no, you can't flip over a "low pinion" axle to make it a "high pinion" axle, nor can you just "flip over" a rear axle to make a front (you probably knew that already, but someone will invariably ask when a thread like this pops up...)
