FM rear brakes (interesting wear) help))
 

So I bought a four corner wilwood BBK from a friend two years ago. He said it had the 1.8 rears and things have been good up until my last track day where brakes seemed to have been fading (variety of issues including health issues, I really shouldn't have been at the track that day.) Anyways had surgery and after two months of recovery I decided to finally inspect the brakes and see what was going on. At first I just thought I hadn't bled my brakes good enough and noticed thermo cracking on the rotors so I ordered new rotors and once I removed the calipers I noticed the pad wear having this weird C shape (pads hang off the swept area.)

https://cimg0.ibsrv.net/gimg/www.mia...823d2234b4.jpg
https://cimg1.ibsrv.net/gimg/www.mia...4a7dc3615d.jpg


I contacted FM and they email back saying they could be 1.8 sports or non sports. Ordered a set of the sports since I already had the non-sports and turned the calipers won't fit over the sports. Curious if anyone else who have this kit has these issues? I know this LBBK is popular with AutoX crowd but haven't read any issues.

I have new Gloc pads ready to go but don't want to ruin them if I can avoid it at all possible.

Were the previous rotors used with OEM calipers before installation of the Wilwoods, particularly on track with high-temp pads?

I'm a software guy, not a mechanical engineer, but as I understand it the heat cycles on cast iron can cause the metal to harden over time in the regions that got hot. It's not a great conductor of heat, so if the rotors had been used on track it's possible that the parts of the rotor on which the OEM-shaped pads rode has hardened but the material further in is still soft. Softer iron means the pads will wear it faster, thus the weird wear pattern.

If so, then a new set of rotors that haven't been previously used with the old pads would fix it.

--Ian

That looks like more pad area than the OEM rear pad on a non-sport rotor. Does the pad covers the non-machined part (in black) like below? If the pad doesn't initially contact the full rotor face, it would have the same characteristics as you posted. I've seen rear rotors with the rotor machined down on the inside, outside, or both.
https://cimg2.ibsrv.net/gimg/www.mia...d1cf65fe27.png

Yeah, the pad does cover the non-machined part as well though just a tiny amount. the front facing side of the rotor, the pad doesn't quite have that much of a groove whereas the backside of the rotor where the non-machined part is a bit more recessed - creates a deeper groove and I feel like it is effecting the stopping power of the brakes. I have a hard time believing this would be acceptable from a company but maybe the way to go is to have the backside machined?

Keep in mind that most "stock" rotors you can buy for a Miata are aftermarket "OEM-equivalents". Equivalent doesn't mean the same, it just means that it's designed to work with the stock components, so an aftermarket BBK that uses more of the swept area than the OEM caliper did may or may not work with any given "OEM equivalent" rotor.

--Ian

Yeah, I understand that bit. Though even the aftermarket OEM-equivalent that came with the kit still shows that same wear albeit not as bad because I swapped rotors soon as I had them and it never saw track use. These were designed for the 10" rotor.

Not sure if it's the same kit, but I'm running the 4 piston FM/Wilwood rear on Sport rotors. This is what the pads looked like with Centric rotors when I installed the kit several years ago:

https://live.staticflickr.com/4613/3...fb9bbfbb_c.jpg
https://live.staticflickr.com/4699/3...dc3dce6f_c.jpg

Installed with G-Loc pads

https://live.staticflickr.com/4602/2...360aa740_c.jpg

Your post is a little unclear, but that wear looks like what you would get if you ran a sport rotor under a caliper with brackets for a non-sport rotor.

I struggle with clarity sometimes hah.

I currently use non-sports, however I was second guessing myself thinking that I possibly had brackets for the sport sized rotors (11") so I ordered the sport rotors to test fit and found out that the sports do not fit, eliminating the equation (brackets being setup for sports)

Roda thanks for the photos. It had me reconsider how I was thinking about the issue. Regardless of bracket if the pad doesn't fit the rotor, there lies the issue. I placed the new pad on two different 3rd party "oem" rotors (non-sport 1.8) and they hang off quite a bit. Maybe these would fit better on a sport rotors and I need to get the brackets for those instead.
https://cimg7.ibsrv.net/gimg/www.mia...61a4273621.jpg
The rotors that came from FM
https://cimg0.ibsrv.net/gimg/www.mia...53ee521d7e.jpg
https://cimg2.ibsrv.net/gimg/www.mia...dfa68352da.jpg
Brembo "OEM" rotors
https://cimg3.ibsrv.net/gimg/www.mia...5088f2c4c2.jpg

That's what I thought you were trying to say, but wasn't sure. ;)