what are they, what applications use them, and why?

Reverse cut gears are for high pinion axles. Ford used them in most of their D44s and D60s. The early ford D44s were low pinion. Jeep has also used them in the XJ D30, and possibly some others as well.

Reverse cut gears are stronger in front when moving forward.

In standard cut gears in the rear, the power is applied to the power side of the gear. In reverse, power is applied to the coast side of the gear. In the front of a regular (low) pinion, the pinion turns in the opposite direction and power is applied to the coast side so the front is weaker than the rear when moving forward. Reverse cut gears allow the power to be applied to the power side of the gear.

Some have argued that this is a disadvantage when pulling a load in reverse, such as pulling out a stuck vehicle, since power is being applied to the coast side of the gears in both the front and rear.

The Toy FJ80 is another application available with a HP front diff. It will work in any Toy 8" housing.

so since a hp diff is basically just a flipped upside down diff, the gears are cut the opposite direction for strength..... so would regular gears work in a hp diff? or do they HAVE TO be reverse cut?

"Flipped upsidedown" isn't exactly the correct way to put it, the diff is specifically designed for a front axle application.

You cannot swap the gears between them, the gear teeth would be 90° to each other.

so since a hp diff is basically just a flipped upside down diff, the gears are cut the opposite direction for strength..... so would regular gears work in a hp diff? or do they HAVE TO be reverse cut?
the tires would be going the wrong direction

the tires would be going the wrong direction
not true...the cut of the gear has nothing to do with the way it will rotate

the tires would be going the wrong direction

now i am no expert, that is why i am asking questions, but if, and i am speaking in hi-pathetical terms here, say i take a ford HP44, and for the sake of simplicity, say that ALL the bearings are a direct swap from hp44 to lp44.

if i was to put a complete gearset, ring and pinion, into a hp44 from a lp44 the tires would turn in the same direction, the gears would just be ////// as opposed
///
to\\\\\\
\\\ .... basicall the teeth would angle in the opposite direction, the only way to make the tires go the wrong way would be to: 1 flop the axle over so that you are driving on the "top" of the tires,
or
2. reverse the rotation of the t-case, and thus the d-shafts, axle shafts and tires.



with that said i just created a new question in my curiouse mind....
doest hte front output on a driver drop t-case rotate in the opposite direction as a pass drop?sice the gears are on the opposite side of the diff housing, and if the front turns opposite, does the rear turn opposite as well???

not true...the cut of the gear has nothing to do with the way it will rotate

haha it seems as though as my mind was working itself into a frenzy, you beat me to my own post

Ring gears between high pinion and low pinion axles are not interchangeable. You can not flip a low pinion and turn it into a high pinion and have it actually work.

High pinion axles are nice as they provide better driveshaft clearance than a low pinion axle (in addition to the improved ring gear strength seen in front axle applications).

High pinion axles are nice as they provide better driveshaft clearance than a low pinion axle (in addition to the improved ring gear strength seen in front axle applications).

Also, in some applications, a high pinion axle provides a better driveshaft angle too.

Low pinion gears will not physically go into a hi pinion housing as the teeth will not mesh. outputs turn the same direction on driver and pass drop tcases, this is why guys can run a hi pinion diff on the passenger side (think custom housing) or how you can swap tcases and front axles from a ford into a chevy and leave the rear axle alone and have everything spinning the correct direction

Low pinion gears will not physically go into a hi pinion housing as the teeth will not mesh. outputs turn the same direction on driver and pass drop tcases, this is why guys can run a hi pinion diff on the passenger side (think custom housing) or how you can swap tcases and front axles from a ford into a chevy and leave the rear axle alone and have everything spinning the correct direction


yeah, after like the second or third reply i thought about it a bit moreand realized that my initial train of thought was well...silly...

still however, i am not really understanding how the gears wouldnt mesh if you put both ring and pinion into the housing....

oh and i know that it wont work, as i have been told that enough, i can see reg ring gear not working with a reverse cut pinion above mentioned meshing issues, but why not if they matched?

maybe i am just beating a dead hors, and this is one of those chemistry situations... it just is, dont wonder why just accept it as the lords word...

Reverse cut gears are necessary in order to locate the pinion above the centerline of the axle. R&Ps are designed so that proper mesh occurs in a very specific location. To start with a typical ring and pinion is a type of bevel gear, more specifically it is a type of spiral bevel gear. With the bevel gear and the spiral bevel gear the center line of the pinion gear, if extended,
would intersect the centerline of the ring gear. Now we get to the hypoid gear which is a spiral bevel gear that the extended centerline of the pinion gear is above or below the centerline of the ring gear. There is at least one manufactruer that further describes a hypoid gear set with the pinion above the centerline of the ring gear as an amboid gear set (commonly referred to here as a reverse cut gear set).

I've enclosed a pic of a bevel gear, spiral bevel gear, a Dana 70 r&p with the pinion below centerline and the same r&p with the pinion above centerline. Note that the pinion will not mesh with the ring gear once it is placed above the ring gears centerline. If you have a r&p laying around you can see this very easily.

Gus

Reverse cut gears are necessary in order to locate the pinion above the centerline of the axle. R&Ps are designed so that proper mesh occurs in a very specific location. To start with a typical ring and pinion is a type of bevel gear, more specifically it is a type of spiral bevel gear. With the bevel gear and the spiral bevel gear the center line of the pinion gear, if extended,
would intersect the centerline of the ring gear. Now we get to the hypoid gear which is a spiral bevel gear that the extended centerline of the pinion gear is above or below the centerline of the ring gear. There is at least one manufactruer that further describes a hypoid gear set with the pinion above the centerline of the ring gear as an amboid gear set (commonly referred to here as a reverse cut gear set).

I've enclosed a pic of a bevel gear, spiral bevel gear, a Dana 70 r&p with the pinion below centerline and the same r&p with the pinion above centerline. Note that the pinion will not mesh with the ring gear once it is placed above the ring gears centerline. If you have a r&p laying around you can see this very easily.

Gus

GUS,
Thank you so friggin much.
i am one of those people who once i have a question in my mind on how something works, it drives me insane untill i figure it out.

this is by far the most usefull post in this thread... thank you again, i get it now