Hi Zack
FWIW:
A front & rear spring can be thought of similarly to a horizontal wood structural beam made up of stacked, flat, horizontal 2x6's, connected together with one bolt in the center of the beam & center of the span..
When a bouncing load is applied, only the "ends" of the stacked 2xs's slide horizontally in shear.
Similarly, if there were shear or horizontal sliding between leaves in the center of a spring, the center bolt would be sheared or cut, just like cutting a piece of wire with a pair of snips; hence, like in structural beams, there is no shear in the center of a beam.
The center spring bolt of the front & rear springs needs to be in a "fixed" position held firmly by the square hole in the cross member.
If this center spring bolt does "not" move, nor the part of the top spring leaf immediately adjacent to the bolt:
A. Why grease it?
B. Why pad it?
C. Just tighten it firmly with the "U" bolts & it will not move nor squeak.
Hope this helps.
