The Spicer Powerlok is a clutch style unit, meaning that inside the unit there are a series of clutch discs and plates, and rebuilding the Powerlok would include the replacement of the chtches and discs. The Auburn style is a cone style, which means that there is a cone shaped disc in there that is forced to contact the side of the case by spring pressure. Eventually the sides of the cone wear out by virtue of contacting the side of the case. There is a small amount of space between the bottom of the cone and the bottom of the case, and as long as the cone has not worn out enough to bottom out in the case, you can disassemble the unit and mill some of the material from the bottom of the cone to keep it from bottoming out and ruining the case. Whatever you mill from the bottom of the cone must be made up in shims on top of the cone as the cone itself and all of the internals must remain the same thickness or the spring pressure is lost.
For the longest time the Auburn style was considered non-rebuildable, but this is not the case. You just can't let the cone bottom out and score the case. And I know this will cause some debate, but the Auburn style is considered a superior design by virtue of its non slip design, whereas a clutch style is only as good as the grip of the clutch and plate material. Hope this helps, and by the way, if yours is the 489 case, resetting up the pinion depth after a gear change is not usually for the do it yourselfer. However, if you are going for a gear change, you may want to consider using the new hard spacer in place of the old style crush sleeve. It makes setting up the gear pattern much easier than the crush sleeve. Good luck with your project, Geof
