I think it depends wether its high or low pinion, think hp uses shims, lp uses crush spacer, which are a bitch to get started and easy to over do. Having done both I think it would be easier to change the axle if you can guarantee the quality of the replacement, imo I would prefer to change the bearings, inner and outer (no point doing one without the other), more pain but you know what you've got..just my opinion.Also I don't think backlash should be affected if the pinion depth shims stay the same but bearing preload needs to be measured..I think...