720 electric clutch

[DWolf]

I recently purchased an electric clutch for my 720 off ebay. I installed it today and noticed a problem! The clutch armature assembly rubs against the outer casing of the clutch field assembly. It creates enough drag to bog the engine down, without the mower on the tractor! I have an old bent armature, when I compare the old one with the new one-the new one is about a quarter of an inch shorter. Am I missing some parts here? Do I need to get some shims to get this to work right? Any help is greatly appreciated