Is a center pin only necessary when you are using shims or spacers with the leaf springs?? I did not have a center pin when I installed the front leafs a while back.. I am about to install the rear leafs with angles shims and noticed the hole for the center pins,,, am I correct in assuming that the center pins are only necessary when using shims or spacers??? Thanks! Just wanna make sure I did the fronts correctly and will do the tears correctly as well!