Case of The Wobbly Steering Wheel II: Pressed Rod Ends Versus Machined Rod Ends

The steering got wobbly, the steering wheel started shaking, the front wheel started shimmying and the go kart seem to be out of control. The boy with his father had just put together a go kart but it seemed to be falling apart  all ready.

What’s going on here?

Well first understanding why a steering system would be shaking is needed.   An analysis, minor analysis, of the steering system needs to be performed. The first question to ask is:

What causes shaking ?

Shaking is caused by in-balances in the system or forces exerting themselves across the system that normally would not happen. In plain English, things are sloppy and the wheels are out of balance. 75% of the time the wheels are out of balance but the other 25% of the time the steering system is sloppy. The sloppiness in the steering usually results from rod ends becoming wallowed out.

A rod end is a linkage point where the end is allowed to rotate in multiple directions. To accomplish this a ball bearing is used. The ball bearing has a hole drilled in so bolts can be fixed to the ball. The ball is held in place by a carrier. What becomes allowed out in rod end is the carrier portion typically.

There are various designs of rod ends the most simple being the pressed metal plates that are formed around the ball. These formed metal plates are what constitutes the carrier section and are usually made up of a lower grade steel so they can be formed.

In contrast there some machine versions that encapsulate the ball using either peaned over metal swages or hardened inserts that are machined and held in place with c-clips or some other sort of hardware.

There are some other types of machined carriers that are pressed together in the manufacturing process.  Heat is used to expand exterior and then the ball is inserted into the joint.

The cheaper rod ends are the pressed metal versions. Typically you can pick them up around 10 bucks a piece or less.  “You get what you pay for” is really what it comes down to. The more expensive versions are harder to manufacture therefore they cost more relative to the pressed metal versions.   Though useful and cheap they have a limited life expectancy. Be sure to understand this before selecting a rod end that is too small for your application.

Typically on a small go kart the pressed rod ends will be okay for a while, but close observation of the rod end needs to be taken especially if the go kart is ridden over rough surfaces where the wheels are constantly being bombarded by gravel and ruts. Racing go karters for example use the machined versions because they are more reliable and there’s a lot of vibration and road load during racing. Additionally to keep the mass of the go kart low, some racing go karters may use higher grade versions that include aircraft aluminum, which is a special kind of aluminum and it is light enough to keep the mass down in the steering system.

Additionally on some of these rod ends a secondary failure is the tie rod carrier or housing interface. This may sound fancy all it means is that the threads on me tie rod and carrier interface are wallowing out. Typically this occurs because the linkage was never tight to begin with. The best way to keep a rod end tight is to make sure that the linkage to the steering knuckle is secure and tight.  Additionally the rod and tie rod interface are locked together using a lock not. The lock nut is jammed onto the tie rod end.  This pressing force from the jam nut is a pre-load that is stronger than any vibration that can occur in the steering system.
Rod Ends are also used in different applications such as linkages  for throttles and linkages for brakes. Additional care will need to be taken on all rod ends to make sure that vibration is not causing the linkages to come loose. Typically the cheaper route and is okay for a throttle and a brake system. Use on a steering mechanism is okay but care must be taken to make sure that the steering system is not seeing excessive loading. Sometimes just an upgrade in the size of hardware and the size of the ball joint or rod end is needed.

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