Heim Joints

When the British shot down a German plane in early 1940 they found a rather interesting connection in the aircraft's control system. This unique connection was what we’ve come to call a spherical rod end. In the UK the patent was given to Rose Bearings Ltd.  That’s why British call them Rose Joints. In North America the H.G. Heim Company was given an exclusive patent to manufacture these joints. That’s why in the United States we call them Heim Joints. They’re the same thing.           

            

High quality economical spherical rod ends really didn’t appear until the late 1970s. A Japanese company, N.M.B, produced these spherical rod ends. The reason they were so economical was that they were selling them for less than it cost them to manufacture them. The United States government asked them to please leave the marketplace so they purchased a U.S. company, N.H.B.B. (New Hampshire Ball Bearing) and continued production. You have to love it.

            

Today over fifteen American companies make rod ends. These products run the gamut from the stamped steel bodies used in control links for garden tractors to the 17-4 PH stainless units found on nuclear submarines.

            

Racecars use Rose-joint or Heim-joint rod ends because they have zero-play and zero elasto-kinematics. A normal automotive suspension arm will have rubber bushings at the chassis ends and a ball joint at the wheel end. Only the extreme street performance cars like the Ferrari Scuderia or Porsche 911 GT3 RS use heim joints.

            

The first joint normally that’s converted to a rose is usually the ball joint. This is because the camber on the wheel can easily by adjusted by moving the ball in or out relative to normal. Next, a serious racer would have rose jointed inner arm bushes and then able to adjust caster and dynamic angle changes during suspension compression and rebound.

Two Types: The standard two-piece heim joint consists of a body (race) and a precision ground and heat-treated steel ball. This is essentially a spherical bearing. This type of construction allows the rod end body to carry a substantial radial static load while at the same time offering substantial misalignment capabilities.

            

Next is the three-piece style that consists of a body, ball and race. This type of rod end features fully swaged bearing construction. The advantage is that there is spherical conformity between the ball and race. The three-piece heim joint also offers increased flexibility since different types of materials can be interchanged in each component part.

Quality Levels: The range of quality is astounding and very confusing. The labels used by different companies make no sense at all. You can buy a 3/8x3/8-24 rod end for $4.37. The same size in aluminum will cost you just over $16.00.

Or, you can pay over $20.00 if it’s constructed of chromoly steel.

            

Pegasus Racing (www.pegasusautoracing.com) has the simplest advice. It the rod end is for the sway bars or the shift linkage just buy the cheapest ones. If it’s for the steering linkage or the suspension then buy the expensive ones. Just stay away from the middle of the price range. The expensive rod ends should have both a hardened ball and a hardened race.

            

Let’s consider how many rod ends you actually need. If you have a formula car or a sports racer I’m thinking 6 to 8 at each corner. Let’s just round it off to 30 so we can work with even numbers. If I buy the cheapest rod ends I can find I’m going to spend around $150. It will at least be under $200. Now lets get the finest we can buy. The bill might reach $600. That means the difference between the cheapest and the best might be less than $500. How much did your last motel bill come to?

Maintenance: Rod end bearings don’t like dirt. Grease is a major issue since it can combine with dirt to create a grinding compound. On racecars the spherical bearings are fully exposed and take a battering from the elements. This means you have to clean them on a regular basis.

        

The folks at Pegasus simply water blast the suspension when they return from the track. Then they blow the excess water away with an air gun. This is followed up with WD-40 to get rid of any remaining moisture. They can do a formula car in less than thirty minutes.
          

Lubricating Teflon lined rod ends won't accomplish anything for you except to make them collect dirt faster. If the rod end is of good quality, and the ball is still snug in the Teflon, dirt isn't a real problem as the edge of the Teflon acts as a wiper, keeping the dirt out. It's only when the ball becomes loose that getting grit inside is a problem. At that point they need replacement anyways.