Rod Ends - Critical Mass

Inside today's street rod, no matter what style, there's a good chance you'll find at least a couple of rod ends, spherical bearings, or, as the Brits sometimes call them, rose joints. Rod ends happen to be one group of components that receives little attention or no added thought. After all, they all appear much the same, and they're pretty much forgotten when they're hidden deep inside the bowels of a hot rod. Unfortunately, rod ends may be one of the most critical hardware pieces on any modified car-street rod or otherwise-and they're components you shouldn't forget about.

Most rod ends are regularly used in places where they're given the task of handling sizeable loads, and there is usually no backup-it's the rod end versus the load. Needless to say, it spells big trouble if a rod end breaks in a suspension or steering component, which is instantaneous. Because of this, rod ends are absolutely critical, and some are truly aerospace quality while others are nothing more than junk, with plenty of different examples in between. Simply looking at a rod end is even more perplexing, since it's difficult to differentiate between a good-quality rod end and one that's more qualified for scrap.

This is a three-piece ("aircraft") rod end. With this configuration, the race is formed around the ball, and then the race insert is staked into the body.

The Bare Bones Of Rod-End Construction
A rod end consists of a spherical ball designed to rotate inside a housing; this ball is the actual bearing, while the housing wrapped around it is the race. The spherical ball has a machined flat on each side, and this modified "sphere" is bored with a hole through the center. That's the bare bones of rod-end construction, but there's more. When scouring the marketplace for rod ends, you'll regularly find "economy" or "commercial" examples.

While there are a number of different economy rod ends available, this is where most of the pretenders come into play, so the only types you should even think of using are the fully formed-or, more correctly, "swaged"-two-piece examples. During manufacture of these rod ends, the body is swaged around the ball so the race on which the ball rides is actually part of the body. If you're checking out lower-cost rod ends for your rod, this is the only configuration that offers reasonable radial or pull-strength coupled with good axial strength, which is the resistance of the ball being pushed out of the side of the body.

Different materials can be engaged in construction because of the three-piece design. This process allows the rod end to best match the application (strength versus load).

Ultimate high-performance rod ends use a three-piece precision layout. Here, the race is formed around the ball, and then the race insert is staked into the body. With this type of manufacture, a much closer fit along with a much higher degree of precision between the ball and the race is provided. Regularly, this three-piece configuration is referred to as an "aircraft" rod end. The three-piece design provides for different materials to be used during the manufacturing process, allowing the rod end to best match the application. Races can be constructed of mild, alloy, or stainless steel-brass or aluminum bronze is sometimes used, but the truth is, it should be avoided because of the low strength. Meanwhile, bodies are constructed from mild, alloy, or stainless steels, aluminum, or even titanium.

Material World
As pointed out earlier, there is a wide range of materials used in the construction of rod ends. Typically, the balls are subjected to the highest loads encountered by the rod end, and, because of this, they require the greatest hardness and of course, the greatest ultimate strength. Certain inexpensive commercial rod-end balls are manufactured from bronze or even sintered steel materials. From a strength perspective, these materials aren't so appropriate, but there's a big caveat: Certain sintered steels are fully up to the job. For example, respected German automobile manufacturer BMW has started using sintered steel for high-stress applications, such as connecting rods. With the right heat treat, sintered steels can live happily in a medium-duty rod-end ball application. Of course, high-quality rod ends normally incorporate heat-treated steel balls, regularly using chrome-moly, stainless, and 52100 bearing steels. The balls must be extremely hard so they remain round, and they are chrome-plated to provide a smooth bearing surface in many cases, which is vital when the ball is placed under a load.

This rod end has a composite Teflon liner, and two- or three-piece rod ends with Teflon liners can be purchased.

Due to the heat treat and overall hardness of the ball, the outer rod-end race must be hard, but not as hard as the ball. Many three-piece rod ends incorporate a race manufactured from through-hardened steel alloy or a stainless steel. In both of these examples, the outer race is heat-treated for wear resistance, and, of course, for strength.

Economy rod ends, on the other hand, usually have bodies constructed from low-carbon mild steels, and it isn't possible to through-harden this material. Although this less-costly material might function perfectly well in a lightly loaded application, rod-end bodies manufactured from chrome-moly or heat-treated stainless steel are far superior in severe-duty applications. The use of chrome-moly or stainless bodies allows the physical size of the rod end to be reduced because the material has more strength. Some manufacturers offer rod ends with bodies manufactured from 7075-T6 aluminum, which is one of the strongest grades of aluminum, and it actually has a tensile strength slightly greater than mild steel. If you compare two similarly designed rod ends, one made from mild steel and the other from 7075-T6, you'd end up with similar strengths. The truth is, aluminum is not as forgiving as mild steel under analysis, since it will not stretch or bend as much before breaking. You'll discover the steel jobs have almost double the strength when a comparison is made between the strength of an aluminum rod end to the strength of a heat-treated chrome-moly or stainless component.

Examine this rod end closely. See how the ball isn't centered? This is the misalignment that the rod end design can handle.

Ultimately, use high-quality heat-treated steel examples, unless you have a very good handle on the limitations of aluminum rod ends, and you're absolutely certain with regard to the loads encountered. The safety margin is much greater.

Teflon Lubrication
The Teflon liner is a very common option seen on rod ends, as it allows the rod end to be self-lubricating, and this liner is important, since it's usually rather difficult to grease or oil a rod end once it's installed on a car. Rod ends with a grease fitting are not a good idea, since the grease fittings can physically weaken the rod end, and grease on the rod-end ball also attracts grit that works its way between the ball and race, ultimately accelerating the wear process.