I need to add a spacer in between a CV joint and a transaxle output shaft drive flange and I am wondering what the best face design of the spacer is, flat or cupped. I noticed that the "flat" surface on a factory CV joint appears to be slightly cupped or dished. It is this surface that mates with the " flat" (also dished) face of the output shaft. Since the CV joint / output shaft is designed so that faces carry the load (not the bolts that pass through the bolted assembly) I was wondering if this cupped face was intentional or just a manufacturing variation. IE is the cupped design used so that when the assembly is bolted together the OD of the assembly mates first and has the highest interface pressure, in order to carry the highest load. Also should my spacer be harder or softer than the CV joint and output shaft hardness for the best torque capability. I was thinking of making the spacer out of an old CV joint and leaving the CV joint heat treatment as is. The CV is locally induction heat treated on the inside where the CV joint ball carrier features are located.
Thanks