What are the downsides of clipping the axle shims when installing an axle?
I am not sure there is a down side to cutting shims other than the possibility of leaks if you stack the cuts on top of each other. I’ve clipped shims many times with no problems. It’s one of the little tricks guys don’t talk about. I often do this to remove shims, and then reinstall a cut shim or two after the clearance is too little, and the wheels turn in the same direction when one wheel is turned. When reinstalling multiple cut shims I alternate the cut positions always keeping the cut sections at the top or as near the top as possible. This way the cut areas do not overlap and cause a deep groove and I don’t have more than two cut shims on a side. Remember the shims come in different thicknesses so I try to cut the thinner, though not the thinnest shims. Cut between two bolt holes and alternate which studs the cut section falls between. I also put a little gasket sealer in the cut area.
You can also insert the edge of a shim or multiple shims to estimate the shims you’ll need to use. The correct clearance between the butt ends of the axles is .002″ to .008″. So, once you have the wheels turning in the same direction you should be able to reinstall just enough shims to equal that .002″ to .008″ clearance. Keep in mind that tightening the bearing retainer bolts to the proper torque further reduces the clearance so inserting .002″ may not be enough to achieve the proper clearance.