A U-bolt serves in four critical roles:
Primarily, the truck U-bolts provide the force required to clamp the lead spring and related components firmly together. In addition to the leaf spring, these components include the top plate, axle seat, axle and bottom plate.
The properly installed u-bolt eliminates any flexing of the lead spring in the are between the U-bolts. This particularly critical since the hole for the centerbolt in each leaf acts as a stress concentration which would lead to rapid leaf breakage if spring flexing was not totally eliminated by the U-bolt clamping force.
By firmly clamping the spring to the axle seat the horizontal forces acting on the centerbolt are greatly reduced which in turn prevents shearing of the centerbolt.
Proper clamping of the spring by the truck U-bolts provides the desired spring stiffness and contributes to maintaining the vehicle ride height and handing characteristics as originally specified for the vehicle
Three basic types of bends are used on U-bolts depending on the suspension design and the shape of the mating parts:
High Tensile Strength that attribute to its durability.
High material hardness that can handle right torque without thread deformation.
Can help to extend the life of Leaf spring due its high tensile strength and high material hardness.
At 100 N-m the thread of competitor’s U-bolt encountered thread deformation
At 100 N-m the thread of U-bolt did not encounter thread deformation