Automotive suspension component attachment is a critical safety issue. When failure occurs, the result is catastrophic. Problems normally result from incorrect service procedures. Understanding the design is crucial when repairing the suspension.
To the casual observer, the attachment of ball joints and tie rods appear very simple. A nut secures the treaded shaft of the component. They often use a castle-nut, with a cotter pin to prevent backing off. Remove the nut, on most designs, and the joint remains firmly attached. This is due to a press fit, achieved by a tapered shaft. The taper-lock feature provides many benefits.
The taper-lock fit
The illustration above shows the stress from a typical bolt on the left and a taper-lock on the right. A tapered-joint is very much like an interference-fit connection pressed into place. As we tighten the nut, the tapered shaft wedges into the bore. This spreads stress of the connection over a much wider area, providing strength. The taper-lock allows no movement or slack in the connection, critical for suspension alignment. With such a tight fit, corrosion cannot readily enter and weaken the attachment. Unlike a pressed-fit, they need no special tooling for attachment.
Non-locking Ford design
Because of the many advantages, the taper-lock design is almost universal. An exception is the Ford non-locking design. They use a straight shaft, with a cone at each end to provide centering. With this design, a locking-nut rather than the castle-nut and cotter pin secure the connection. They require replacement of the nut, when removed. Because the connection does not lock, the stud can rotate when tightening. This makes achieving proper torque more difficult and failure of the nut means the joint may come apart. Anyone working with such a system must be very careful.
Removing a taper-lock joint
Taking apart a taper-lock joint can be difficult, without experience. Beating on the threaded shaft will destroy the part, and usually not separate the connection. Several tools are available that may help.
Many ball joint removers are small screw-operated presses. These apply force between the stud and knuckle and break the press-fit. A problem is, each tool is unique and many are needed service common vehicles. These tools may damage the rubber grease seal that ruins the joint. A more universal method is the “pickle fork” tool. The user drives this into the space between the joint and knuckle and wedges the connection apart. It also damages the joint, so it is only useful when we intend to replace the part.
Most trained technicians use the hammer method. With skill, no damage is done to the joint, boot or knuckle. One sharp blow to the knuckle causes the taper to distort slightly. This separates the components quickly and without permanent damage. The method requires a great deal of finesse and takes time to learn. Continually hammering on the knuckle will damage it. This method will not work with stamped steel or aluminum components, but give good results otherwise.
Ball stud breakage
A broken tie rod or ball joint stud means disaster. The wheel will come off or steering will be lost if these parts fail. The cause of the break is not the stud. Damaged, worn or distorted mountings cause the failure.
A taper-lock that is not tight will cause wear to the knuckle. When distortion exists in the tapered-hole, locking is not possible. This supports part of the stud, and we generate tremendous stress. This force will cause the stud to fracture. Not tightening the joint properly, during assembly, is the most common cause of wear. An impact can also bend the stud and damage the hole.
When a ball joint or a tie-rod is found loose, we must very closely inspect the knuckle. Any distortion of the mounting hole or raised metal around the hole requires replacement of the part. Simply tightening the connection can cause the stud to break.
With taper-lock joints, tighten the connection and then loosen the nut, to make sure we lock the stud. If the stud comes out when we remove the nut, there is a problem. Replace any suspected parts or have them inspected by a professional.
With understanding, service of suspension components is easy. With a little care, we easily avoid life-threatening problems.