I didn't find this problem addressed in the the absurd amount of usage I did with the search so, I thought I would address this issue if not already covered.

Upon an obscene amount of grinding to make hubs out of my old rotors, I discovered tonight while driving out the studs... they are not all the same between rotors.

The rotors are from my 91 RS. I don't know the history of it and who knows about the brakes.
I did find that the studs are not the same between right an left though. Leaving me with a slightly cold feeling knowing that I have to throw one away after hours of labor and getting a chunk of iron stuck in my eye.

Make note if the stud does NOT have an 'M' (I assume since it's not underlined) and the head is mushroom shaped and 3/4" wide, the longer doorman/motormite/napa studes will not fit. They will be too small on the knurl (or spline, whatever it's called).

Just thought I'd put this out there before someone else pisses away their time or $$ and runs into the same issue.

 

woah, thats weird. When I did mine, I remember the new studs I bought were shorter, but the splines were the same. I never even paid attention, I would have been pissed if I split my hub cause of something like that. I only say that because I would have forced them in there one way or another lol.

 

Well, here is the problem I ran into...
The original studs on one rotor have an 'M' stamped in the tip of them (where the thread starts), that is the one pictured on the left above. The new, longer dorman (p/n 610-323),motormite, napa, studs are the same size/roughly spline but, longer.
The stud pictured above on the right is considerably larger in dia. at the splines and head. The new (dorman/etc) studs will nearly fall through the holes in the hub that these larger splined studs were driven from. If that remotely makes sense.

This may be some oddball replacemant rotor (as both are obviously replacements after a junkyard scour after work today) but, I just though I'd bring it to light so this doesn't suprise anyone else. I'd really hate to see someone else have the 'oh f--- me running' moment I had when I realized the problem.
Crappy aftermarket replacement parts...

 

Deadbird, you can just drill out the outher ones to the larger size and order some ARP studs in that knurl to fit. I did this on my brake upgrade and drill my hubs uot to accept ARP 1/2" studs with a .568 knurl rather than the 12mm factory studs with the .485 knurl. I used a 35/64 drill bit (.547 holes)
Dean

 

I found the answer = .3 of an inch. Man was that an angry discussion.

I read in a post here that the person used new 1LE rotors to avoid the need for a spacer? I was planning to use my IROC rotors for the hubs. Does the location of the wheel relative to the fenders change enough to be noticed?

Maybe one of those questions but if I don't ask then I remain in the dark.