General Axle Information - Basics
Semi-Floaters
Full-Floaters
Integral Carrier Design
Removable Carrier Design
Reverse-Cut vs. Standard-Cut
Semi-Floaters: |
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In applications like heavy duty 3/4 and 1 ton trucks, semi-floaters are much less desirable because the heavier weight of the vehicle combined with the twisting forces can cause semi-floater shaft to bend or break. Obviously, having your rear wheel pass you on the road can be somewhat unsettling. To prevent this from happening, full-floaters use an axle housing with a spindle formed at the end of the axle tube. The wheel is bolted to a separate hub, which spins on two opposed, tapered roller bearings. Since the weight of the vehicle is supported by the spindle on the housing and not the axle shaft, the shaft is only subjected to twisting forces form the engine. (taken from FourWheeler Jan, 1999) |
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Common examples of integral carrier housings are: almost all Dana axles, GM corporate axles and some ford axles, like the 8.8 or 10.25" full floaters found in F-Trucks. This style of housing is easily recognized by a center casting with tubing pressed in from either side. The tubes are pressed very tightly into the casting, and are plug welded so they will not twist or pull out. There are bearings in the end of the housing to support the wheels, and this type of housing is commonly used for both full-floating or semi-floating axles. This design can also be recognized by the removable cover used for gear inspection and installation.
The Ford 9-inch and Toyota rearends are good examples of the removable carrier design. These rearends use a housing made from several pieces of stamped steel that have been welded together as a single unit. The gears are contained in a bolt in center casting commonly referred to as a "third member." The third member is inserted into the housing from the driveshaft side of the rearend, and is held by a circle of bolts. Drag racers enjoy this style of rearend because they can set up different gear ratios in multiple third members and quickly change ratios between rounds. This type of rearend usually has no removable cover; in order to inspect the gears, you have to completely remove the axle shafts and drop the third member from the main housing.
Often mistakenly referred to as "reverse rotation," the term "reverse-cut" is perhaps the single most misunderstood term by four wheelers and even many in the axle business. A reverse 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 direction 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 vehicle 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 practice 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 front 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 above the centerline of the axle shaft. Therefore, standard cut gears are always strongest when used in rear axles and reverse cut gears are stronger 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 large 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 sometimes 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 stronger for front 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 axle are not interchangeable. Standard cut gears cannot be used in place of reverse cut and vice versa. The housings are also not interchangeable. However, differential 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