Rod Ends Part II

Rod ends

In our last segment on Rod Ends, we examined the basics of construction along with a look at specific materials. If you recall, the “good” racing rod ends were the aircraft style jobs. They incorporate a three-piece layout and for the most part are built with robust steel materials. This time around, we’ll devote space to the liners inside the rod end and we’ll also examine rod end misalignment. Check it out:

Teflon Liners…

A very common (and good) option you’ll find on rod ends is the Teflon liner. The liner allows the rod end to be self-lubricating. This feature is important because it eliminates the need to grease a rod end once installed on your racecar. What about a rod end with a grease fitting? Stay away! They’re not a good concept, because drilling a hole in the rod end for a grease fitting weakens it (much the same as a driveshaft universal joint with a grease fitting). Besides, grease or oil on the rod end ball actually attracts dirt, which in turn, promotes wear on the ball/race.

When a Teflon liner is used, the need for lube is pretty much history. Please note that Teflon is a DuPont product. They invented it, and Teflon is their name brand. There are other PTFE (Polytetrafluoroethylene) products out there that are not manufactured by DuPont. A Teflon liner consists of a carrier component, often a fabric, that provides compressive strength, a Teflon component for lubricity along with various bonding resins. The Teflon liner is bonded to the race which means the rod end ball physically rotates on the liner. As the ball moves, Teflon rubs on the ball. That of course provides lubrication. Rod ends with Teflon liners are manufactured in two or three piece configurations but watch out for cheap rod ends assembled with virgin Teflon. Virgin Teflon is comparatively soft. It has a compressive strength of (+ or -) 10,000 pounds PSI. Compare that to a high quality composite Teflon liner, which usually has a compressive strength of somewhere between 40,000 and 60,000 PSI, and you can see there’s a huge difference. There’s something else too: A quality Teflon liner eliminates extra clearance between the ball and race. This means the ball and race have a much tighter fit.

Something else to consider is this: If a manufacture adds Teflon liner to a rod end, that doesn’t always mean it’s a precise piece. Additionally, it doesn’t mean it’s a high performance piece. When you’re shopping for rod ends, you’ll probably come across a phrase that includes the words “beating out”. Beating out regularly refers to two very different situations. The first involves the deformation of low strength “self lubricating” liners. Some cheap rod ends are built with races constructed from molded plastic (sometimes they’re mixed with a fiberglass filler). They can also add a small amount of Teflon for increased lubcrication. Sounds fair enough, but cheap rod ends such as this might look and sound like trick, but they usually have a compressive strength of 15,000 PSI or less. Under a given load, the race can deform. And you might not see it because the body can be undamaged.

The other form of “beat out” is when the liner of the rod end becomes detached from the race. This is caused because the bond isn’t sufficiently strong. Keep in mind that because of the self-lubricating properties of the liner, some manufacturers can’t get the bond right. Additionally, when a rod end experiences high misalignment, small fragments of the liner can be destroyed. That erodes the liner and before long, the clearances within the rod end will increase to the point that it is unusable. There are no set standards for the liner bond strength, aside from Uncle Sam’s MIL Specs for Teflon-lined bearings.

Rod End Alignment…

We talked about misalignment above. Here’s what it’s all about (and it’s important): If you recall, a bolt, stud, or some other form of fastener goes through the hole bored through the center of the rod end. That means the ball inside the rod end becomes limited with regard to rotation (a full 360 degree rotation is obviously out of the question). Due to this fact, all rod ends have definite limitations on how far they can be “misaligned” before the sphere becomes bount up in the housing. What you’re dealing with is the “angle of misalignment” and it’s important when selecting a rod end for a given task. As it turns out, not all rod ends are designed to accept the same degree of misalignment as others. That’s why misalignment angles are published in the specifications of most high quality rod ends. Fair enough, but so what if you exceed the manufacturer’s recommended maximum misalignment angle? At least, you’ll end up with early rod end wear. At worst, you’ll bind and break the rod end.

That’s not good, so how on earth do you figure out the misalignment angles? It’s not that difficult to check the angles: Remember that grade school protractor you had? You can use it to check the geometry. Compare that to the “angles of misalignment” laid out in the manufacturer catalog. By the way, you can attempt to shortcut the job by simply using a big honking rod end, but in truth, that won’t fix the problem. That’s why manufacturers build high misalignment rod ends.

That’s a wrap for this issue. Next time around we’ll dig into sizing rod ends along with the right way to “clock” them on your racecar. It’s important. Stay tuned.

Rod ends
The rod end shown here incorporates a composite Teflon liner. You can buy two or three piece rod ends with Teflon liners.
Rod ends
The Teflon liner is bonded to the race so that the ball actually rides on the liner. The movement of the ball rubs Teflon on the ball, which in turn provides the necessary lubrication.
Rod ends
See how the ball isn’t centered in this rod end? This is amount of “misalignment” this particular rod end design can accept.
Rod ends
This shows the amount of misalignment (calculated in degree of angular movement) a ball or sphere can accommodate without encountering interference. See the large shoulder on the ball? That means it is a high misalignment rod end.

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