installing new rotors

[irishfan77]

I was installing my new rotors on my project. I bought the modular spindles for 73-87 for my dropmember project. I bought drilled and slotted rotors from summit for them that are factory size 12". I put my bearings and dust shield on and put the castle nut on and backed it off like everyone said and now I have a good 3/16 play front to back. this is not normal right? Am i missing anything, or does anyone have a diagram of the procedure. I used the old castle nut from my original spindle, should I have used this or gotten a new one. Any help would be appreciated!!