Full-Floating vs. Semi-Floating
Any drive axle must be capable of performing two functions: Support the weight of the vehicle safely and transmit power to the wheels for propulsion. By design, all steering (front) drive axles are full-floating, but rear drive axles may be semi-floating or full-floating.
The semi-floating axle design fastens the wheel directly to the flange on the outboard end of the axle shaft and a single bearing supports the outer end of the shaft. The axle shaft has to support the weight on the axle and the propulsion forces from the engine twisting it. The semi-floater is standard on most sport-utilities, half-ton and light-duty 3/4-ton pickups. This Dynatrac design is lighter and less expensive than a full-floating axle, and suitable for 5/6 lug wheel applications up to 4500 GAWR.
In this design, the wheel is fastened to a separate hub which rotates on two large, opposing, tapered roller bearings secured to a spindle on the outer ends of the axle housing. All of the weight is carried on the hub and two large hub bearings, while the axle shaft goes through the hub and handles only the twisting force from the engine. With more than double the bearing area, and no bending forces acting on the axle shaft, the full-floater is standard in most 3/4-ton HD and 1-ton pickups. It is the design of choice for heavy payloads or trailers, big-block and turbo diesel engines, and very large tires, up to 10,000 GAWR.
Which is Better?
Full-floating setups are a must for 3/4-ton and heavier trucks, and a good idea for 1/2-ton trucks that haul a lot of weight, tow heavy trailers, or see severe 4WD use. However, except for Dynatrac custom axles, virtually all factory full-floating rear ends use 8 lug wheels, so if you have invested heavily in 5- or 6-lug wheels, you may be better off having us construct a rear axle for you. Dynatrac specializes in custom Dana 60, 70 and 80 rear axles in full-floating and semi-floating versions to fit a broad range of trucks from Jeeps® to 1-tons.
Reverse Cut vs. Standard Cut
Perhaps the single most misunderstood axle term is reverse cut, often mistakenly referred to as reverse rotation. A reverse cut housing is not a standard cut housing turned upside down, it is a specially designed housing. The term "reverse cut" refers to the direction of the spiral cut in the ring gear, which is opposite that of a standard cut ring gear: Contrary to popular belief, it does not run backwards or in reverse. The principle behind a reverse cut is to strengthen the operation of the gear when it is used for a front driving axle application.
Hi-pinion or reverse-cut axles have also become very popular as rear driving axles in short wheelbase vehicles with suspension lifts because the higher pinion improves drive line angles so well. Dynatrac was among the first to pioneer this application and continues to offer the very best and strongest Hi-pinion axles available anywhere.
Standard-cut axles are often used as the front driving axles because of clearance issues, gear ratio availability, cost, or suspension considerations. However comparable reverse-cut axles have the distinct advantage of overall ring and pinion gear strength.
Reverse-cut axles should be used in the rear when higher ground clearance, reduced drive shaft angles or short wheelbase are desirable issues. Reverse-cut rear axles should be avoided for heavy GVW vehicles or heavy highway towing. Dynatrac has thoroughly tested Dana 44 reverse-cut, and Ford 8.8 reverse-cut, rear axles and found them to be weak and prone to failure in all but the very, very lightest duty applications. We can only recommend Dynatrac’s proven Dana 60 reverse-cut design as unquestionably dependable even under adverse situations.
The gear sets 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, which have different lubrication passages, are also not interchangeable. However, differential cases (open, l/s, or locker) are compatible with both styles, as long as case spline count matches the axle shaft.