The shims are the large like 4 inch diameter washers that are or were on the 4" (about 4", not sure of actual diameter) pivot tube. The tube needs to slid in and out of pivot frame maybe 1_8 to 1_4 inch as axle tilts sideways. Should have been taken out by installer and axle adjusted for mud hog use. If you need more details, I think I can find the installation manual and help you furthur. Ted CenOH