Hendrickson is the leader in manufacturing Auxiliary Lift Axles for trucks such as dump trucks, cement mixers, and garbage trucks. The auxiliary axles are lifted up off the road when the truck is empty and lowered down to the road when the truck is full which permits the truck to carry heavier loads. Many of the auxiliary axles are passively steerable, that is the friction of the road causes the wheels to turn in the direction of the truck's turn, which improves handling and tire wear.
The trucks on which the Passively Steerable Auxiliary Lift Axles are installed frequently go off road to quarries, construction sites and landfills. Because the tie rod connecting the two wheels is on the rear of the axle assembly, it is exposed to damage when the truck is backing up. When the rigid tie rod struck a boulder, tree stump or other immovable object it would be permanently bent, throwing the wheels out of alignment. A bent rigid tie rod would have to be replaced at a significant cost.
In response Hendrickson developed a completely new tie rod made principally of spring steel, which bends if it strikes something and then returns to its original state. This innovation has essentially eliminated the damage that was occurring and eliminated customer complaints. The innovation also allowed Hendrickson to eliminate the spring on the shock absorber and thus reduce both the weight and the size of the axle assembly. Lubrication of the tie rod end was also eliminated and the new design permits toe-in adjustment to be done for both wheels by making an adjustment at only one end of the tie rod rather than adjusting both ends of the tie rod as was required with the old design. Finally, when one wheel strikes something like a curb or a large rock, the flexible tie rod keeps the opposite wheel in alignment with the direction the truck is traveling.