This isnt really a "new" issue... in fact, it's rather common when using various manufacturers in any given build.

What I have observed with some of the newer hat's... and in specific to the newer offerings from various manufacturers... is that the hard coating/anno thickness is the most likely cause for the dimentional changes of the hole. There is no standardized coating thickness and at times when new parts are created or when you source 'other' companies for coating hard parts... it can go sometimes unnoticed. Next would be an insufficient chamfer for the portruding knurl shoulder of the fastner itself. With the available manufacturers for fastners... it falls under the same premise.

Since there is no real common diamention for this peticular (issue) process... as the variables are too great between manufacturers, pre-assembly becomes paramount, to address the unknown.

I believe the easiest solution, would be to simply ream the flange side of the hole. Machining isnt really necessary.

GT.........I just ran into this very same problem on my '68 Road Runner (with the 8-3/4"). The studs are 0.50" diameter at the thread but then step out to 0.615 shoulder right before it goes into the flange. I took a 5/8" drill bit and adjusted the depth on the drill press so that it wouldn't go all the way through the rotor. This essentially put a 45deg chamfer on the hole and let it bolt up flush.

I also had to take a die-grinder to the center hole on the rotor as it wouldn't clear a minor step in the center cap. I had to take off approx 0.10" on the rotor in order to get it to bolt up flush.

I spoke with both Frank and Dustin (Wilwood) yesterday and was told that was the easiest solution.

FYI.........I have the same rear brake setup you're installing and am also going to run Forgelines.

Thanks folks. I did as suggested and lightly sanded the inside of the rotor stud holes with a barrel sander on a drill press. Everything slides together fine now. The forgelines have enough of a chamfer on the backside of the stud holes to clearance.

Thanks for the help. :hail:

Excellent.