High-Performance Differentials, Axles, and Drivelines. Joseph Palazzolo
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href="#ulink_b17de2a1-f723-5655-a53c-15b074214edd">Axle Shaft Retention Methods
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)
In this cross-section view of a typical full-float wheel end, the axle shaft can be removed from the axle housing while the wheel is still on. The vehicle load is transferred from the wheel hub (light blue) through the bearing (purple) to the axle tube (yellow). The axle shaft is isolated from vehicle loads. (Dana Holding Corporation)
C-clip eliminator kits are available in the aftermarket to convert C-washer axles to this type of captured bearing retention. Keep in mind that this is still a semi-float-style axle. Since it is not a true full-float axle, but awfully close, it is referred to as three-quarter float.
The full-float wheel-end arrangement is such that the axle shaft only experiences torque. The wheel-end bearing transfers load from the axle housing to the wheel hub. This type of axle is easy to spot by the bolts on the outside flange of the axle shaft that hold the axle shaft in place. The axle shaft drives a separate wheel hub that supports the wheel structure. These are typically found on larger axles in three-quarter- and one-ton trucks.
And there is another method to identify this axle: If you can remove the axle shaft with the vehicle on the ground, it is a full-float axle.
To determine if your vehicle has a full-float wheel end, closely examine the axle-shaft-to-wheel-hub attachment. If there is a wheel hub, you have a full-float axle, but the presence of the wheel hub may not be obvious. In order to visually tell, look for a series of bolts arranged on a smaller diameter than the lug studs that attach the axle flange to the hub.
The axle beam portion or tubes can be a series of stamped-steel pieces that are all welded together like the banjo-style axle, or they can be actual round-shaped tubing. The preferred tubing for this is called Drawn Over Mandrel (DOM) tubing. Most Salisbury-style axles use DOM tubing for the axle tubes. This style of tubing is also commonly used for driveshaft production. DOM tubing has great strength and consistent wall thickness properties that make it ideal for axle tubes.
You’re looking at a rack of full-float axle shafts. Each of the axle shaft flanges has a series of clearance holes to allow the bolts that hold them in place to pass through. On some of the axle shafts, there are three holes clustered together for applications that have alignment dowels on the hubs. (Randall Shafer)
The tube material for axle housings can be made from a variety of different diameters and wall thicknesses. Here are some sample pieces of the some of the more popular sizes
There are a few different methods to manufacture tubing like DOM and seamless. The tubes actually start out as solid bar stock and are then pierced. Subsequently, the steel is heated, drawn, and formed into the correct shape. Then a mandrel or fixture is positioned inside the tube while the outside of the tube is pulled through a die. This basically sizes the inside and outside diameter of the tubing and thus the name drawn over mandrel. The diameter and wall thickness of the axle tubes is important in the overall axle strength. Some axles have very small diameter tubes and are therefore more prone to bending.
In most enthusiast circles, nothing provokes more debate than the topic of the best differential. When it comes to Chevy versus Ford versus Mopar differentials, everyone has an opinion on which performs better. The same heated conversations begin when discussing Ford 9-inch versus Dana 60 versus GM 12-bolt. Everyone has an opinion. Some opinions are based on valid information. However, some opinions are based on outdated information, not unlike the camel-hump small-block Chevy cylinder heads that were all the rage years ago. Now, with all of the aftermarket support available, unless you want to build a numbers-matching or nostalgic engine, aftermarket aluminum heads would deliver far better performance than the stock units.
Independent of any of this information, common sense should always prevail. As these axles, and the cars they came out of, become older and scarcer, more and more axles show up on the market that have been modified incorrectly, bent, and generally abused. Unless the housing is extraordinarily rare, a used part should be avoided. Alternatively, if you are planning to install new tubes and refurbish everything else that is involved, and then go ahead and buy an axle that has been excessively welded on or shows signs of damage, just be sure that you pay appropriately.
New aftermarket complete axles may not be as expensive as you might think. Keep in mind that by the time you purchase a new gear set, differential, bearings, seals, axle shafts, and brake hardware, you may be only a few dollars short of a