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A complete ICA from a Jaguar XK8 connects directly to the rear suspension. The black halfshafts connect the axle outputs to the wheel ends. This ICA also uses the jiggle-style vent cap on the top of the axle cover discussed in Chapter 1. (Randall Shafer)
The current Corvette axle is unique in the fact that the pinion is located behind the ring gear when the ICA is installed in the vehicle. The pinion shaft is actually hollow and driven from an internal spline in the head of the pinion. Conventional pinions are driven from an external spline at the tail end of the pinion. The Corvette pinion is also very short with a small distance between the pinion bearings. Using large pinion bearings makes this arrangement possible and provides adequate support for the pinion gear.
The front surface of a Corvette ICA bolts to the rear mounted transmission. The outputs to the halfshafts are on the right and left. Note the extensive use of cooling fins and the side covers on both sides. There is even a rear cover on this axle. It tends to resemble a square box more than a traditional axle.
Rear-Cover and Side-Cover Housings
There is a subset of ICAs defined by the cover style or split line of the axle housing. Most ICAs have the axle cover split line like the Viper axle, which is parallel to and just behind the output shafts. There are some that utilize a side-cover design like the Corvette. There are many schools of thought regarding which design is better. But one issue that all agree on is that most side-cover designs today do not easily lend themselves to visual pattern checks and traditional gear backlash inspection. Since the side cover is required to properly support the differential bearings and subsequently the hypoid ring gear, you cannot see the pattern or check backlash unless the cover is removed. If a large access port were available, a pattern and backlash check could be performed. The other method is to assemble the unit and rotate the pinion to disburse the pattern compound, and then remove the cover to check the pattern.
An internal spline in the head drives the Corvette hollow-style pinion. The traditional-style pinion is next to it for comparison. That pinion head bearing is almost as large as the pinion head itself.
The venomous Dodge Viper ICA, easily spotted by the snake on the rear cover, is based on a combination of Dana 44 and Dana 60 internal components. This ICA uses a four-point mount system, two on the rear cover and two more on either side of the pinion. This is also a more traditional rear-cover design than the Corvette side-cover.
ICAs have been manufactured in both cast iron and cast aluminum. The cast-aluminum units have a thermal-expansion and gear-alignment issue that needs to be taken into account during the design process. Aluminum expands and shrinks at a faster rate than the steel gears inside the axle. Depending on the design layout of the gears and bearings, when the aluminum axle housing heats up from normal operation, the gears may be shifted out of their ideal mesh point. Also, the pinion bearings typically increase in preload, while the differential bearings lose preload. This can turn into gear noise at elevated temperatures in the axle.
If the axle receives a cool stream of air while driving to help maintain the temperature, this heating of the axle housing is minimized and these problems do not exist. The typical ICA is tucked up under the vehicle, and does not usually receive adequate airflow. This is important if you are going to stick one of these axles under your muscle car; the transmission will have poor airflow, but also increased torque well beyond the factory design limit. Many manufacturers are now going back to cast iron for their ICAs in order to eliminate the concerns that come with an aluminum structure.
The Cadillac CTS axle housing is cast aluminum and not only has a side cover but also a pinion-cartridge arrangement. The side-cover arrangement and combination of the pinion cartridge make this a unique axle arrangement to service, as most axles are not assembled in this fashion.
Just like other items previously discussed, axle shaft retention methods fall under the axle housing category. Some folks refer to the axle housing as semi-float when they mean to say Salisbury.
Let’s clear up this confusion now. There are three main types of axle shaft retention: semi-float, three-quarter float, and full-float. The type of axle-shaft retention is typically easiest to distinguish based on the bearing arrangement at the wheel end.
Semi-float axle shaft retention is most commonly found on passenger cars and light-duty trucks. It is arranged so that the vehicle loads react to the axle shaft. It is the simplest and most cost-effective design for vehicle manufacturers. This is the traditional C-washer-style axle shaft retention.
The axle shaft has inherent endplay between the differential pin and the C-washer pocket in the side gear. The endplay increases if the optional limited-slip differential is a plate style, and the plates wear over time. The wheel-end bearing arrangement is typically a roller bearing that rides on the axle shaft. The axle shaft itself experiences torque as well as a bending load that results from supporting the weight of the vehicle through the wheels. The path of wheel loads goes from the wheel, to the axle shaft, to the bearings, and finally into the housing.
There is another method to retain the axle shaft for semi-float retention. Here, the wheel-end bearing is pressed onto the axle shaft. This style of axle shaft retention is commonly referred to as the captured bearing or Ford style. Although this is a three-quarter-float, it is not commonly called this. There is a bearing retainer plate that bolts to the end of the axle housing. This bearing and retained plate are pressed and secured on the axle shaft. The Ford 9-inch-style axle shaft is an example. This style of axle retention has a distinct advantage over a typical C-washer arrangement, since a broken axle shaft does not necessarily allow the wheel to separate from the axle housing.
Here you can see the typical semi-float wheel-end bearing arrangement. The wheel end bearing spans across the housing and the axle shaft. The bearing (yellow) and spans the axle housing (blue) and the axle shaft (green). (Dana Holding Corporation)
The axle flange has a socket clearance hole so you can gain access to the captured bearing bolts. This is another telltale sign that your axle has a three-quarter-float bearing arrangement. (Randall Shafer)
The three-quarter-float wheel end has not only captured bearing but also reduces axial endplay. The axle shaft still carries the vehicle load. Notice that the vehicle load is transferred from the wheel studs to the tapered bearing pack arrangement through the axle shaft. (Dana Holding Corporation)
