stock calipers have plenty of flex. Don't doubt your theory. Also, I am sure there could be flex in the brackets...

Smoking Gun
 

Caliper brackets had matching marks:
https://www.miataturbo.net/attachmen...1&d=1408151779

https://www.miataturbo.net/attachmen...1&d=1408151779

Hit the brackets a bit with a grinder to give plenty of clearance:
https://www.miataturbo.net/attachmen...1&d=1408151779

Hit the track today. No more issues. Braking was excellent.

It's Back . . . .
 

Went to Eagle's Canyon for the first time today. Eagle's Canyon is a really different layout from MSR. There are no high speed corners to speak of and lots of 90ish to 40ish braking. Plus, it was friggin' hot. Bank thermometers were showing 107F during my drive home. This is the layout:

Anyway, in the later laps of the sessions, the gritty feeling re-appeared. The pedal was still hard and the car would stop fine, but the feeling hardly inspires confidence especially when combined with ECRs rough surfaces in the braking zones. When I got off track, I noticed the transfer layer on the discs was splotchy rather than smooth.

I have Goodwin's V1 BBK on the car (installed by PO). This kit uses the Wilwood straight-vane vented rotors on the front and steel rotors on the back. Perhaps the rotors aren't up to this kind of braking in the heat? I'm thinking about upgrading the fronts to Emilio's directional vane (they're more than 50% used up anyway) and returning the rears to OEM iron.

???

That sounds like deposition. I suggest cutting the rotors and rebedding. Deposition is more often caused by not performing enough decelerations to build a complete transfer layer. Take a look at the front rotors after bedding.

https://www.miataturbo.net/attachmen...ine=1408890929

Yep, I think I did a lousy bedding job. For starters, I street drove it before attempting the bed-in on track.

Question, will street driving affect the bedding after it's done properly?

No harm to drive on street. That just helps seat the pads. On a new pad and rotor, there isn't 100% contact and that takes a bit of light driving to achieve sometimes, particularly in the rear. The pads require curing to bake out the adhesives. That's the big odor and partial fade you feel during bedding. Once you get that big odor, shut 'er down. I do my best to get it back to the paddock using as little brake as possible. Park after they have cooled a bit, even one slow lap around paddock perimeter. One session later they'll have cooled enough to get some curing done. In a perfect world, you can let them set overnight just as with heat cycling tires.

Block off your ducting when bedding the rotors and/or pads - no sense in working harder than you have to, you want heat in this case, and with the bigger/better brakes up front it can take some work to get them up to temp on public roads.

BUT, Because Texas, you probably have a 20 mile straight county road next to your house, and don't face the brake bedding problem I do embedded in the middle of a metropolitan area :)

I use AC foam in the ducts.

And, yes, I should have bedded them on one of the long, empty roads around here (except for the darn coyotes anyway). I foolishly waited until I was at the track and then I did a rush job. Mea Culpa.

Follow up.

Apparently, there is a materials incompatibility between Carbotech XP8s and steel rotors.

I've been dealing with this through several track days. Finally, I pulled the V1 rear BBK and returned my rear to OEM 1.8 status. What a difference!

What really got your attention was backing the car. The rear would make a loud, nasty racket like you were driving over loose gravel or and axle was loose or something. Just weird and rough. Turns out it was those steel rotors grabbing and fighting with the pads.

I would imagine a V2 BBK with iron rotors would not have the issue. But I'm happy with where I am now . . . adjustable prop valve makes everything easy to balance.

So, my review of the V1 rear BBK from Goodwin? Between component contact and materials incompatibility . . . pure street bling. A D-. I guess I'll sell them over on CR or m.net or something.

The steel V1 rear rotors pretty much suck all around, yes. The iron V2 rotor rings fix this problem and make them work like you'd expect them to. The last time I bought replacement rear rings they weren't particularly expensive, although I don't see them on the Goodwin site any more.

The Goodwin kit came with button-head screws, the flat-side allen bolts are from the V3 kit that used the Racing Brake rotors (now discontinued). The clearances are definitely tight with the flash on the rotor bracket. I used aircraft bolts on mine which required the grinder for clearancing as well.

--Ian

I get the same with Sport rear rotors (OEM Cast) and XP10, with no mounting hardware trinkets.
Just learn to live with it, or get the pads working with the trinkets (maybe work harder on the bedding).

But if you want to look cool at the Home Depot lot, the reversing sounds can ruin your day.
Keeping the rear pads bedded on the street is impossible though.

Weird. I never had any issues with XP8 or XP12 on the sport rears. On the street, there was the expected sometime squealing and the prodigious dusting. But I never noticed anything with regards to reversing. They always seemed to be bedded fine as well.

With the XP8's I had probably at least 15km of street mileage. The XP12's were just to/from the track.

Do you have a prop valve ? I run those XP10-12 in the rear and they're quiet. Even when backing up. Maybe you need to adjust those rear calipers.

The setting of the prop valve don't matter much when you don't apply any pressure. For my usage I tend to adjust the handbrake a little loose but I assume the play without the trinkets is the biggest factor.
I know what it is and it don't bother me.

sorry for being late to the conversation and misinformed about what is available.... Who is selling a "Steel" Rotor? Steel and aluminum rotors have the braking property of cheese.. munster to be exact.

The Goodwin version 1 kit used steel rotors on the rear when it came out (about 10 years ago at this point). I believe this is because Wilwood didn't offer a cast iron rotor-on-hat in the appropriate size at that time. The steel rotors were unsatisfactory, and when a cast iron one became available (might have been a custom size) they were replaced in version 2 of the same kit.

--Ian

Emilio,
Ive Worked with some Top teams in motorsport.. Excuse me when i ask why you would want brake pads to "cure"? Ive never heard of a team doing this nor have I ever hear any brake manufacturer recommend this...

See discussion here regarding "green fade":

Stock Brake System Bed-in

Maybe no brake pad manufacturer uses the term curing, but that is whats taking place. When the adhesives are baked out, the remaining matrix is harder and more stable. That is the very definition in curing in the context of polymers and composite matrices.

From Wiki

Curing is a term in polymer chemistry and process engineering that refers to the toughening or hardening of a polymer material by cross-linking of polymer chains, brought about by electron beams, heat or chemical additives.

Other random site:

Process during which a chemical reaction (such as polymerization) or physical action (such as evaporation) takes place, resulting in a harder, tougher, or more stable linkage (such as an adhesive bond) or substance (such as concrete). Some curing processes require maintenance of a certain temperature and/or humidity level, others require a certain pressure.

For the record nobody needs to do this with brake pads.. yes i understand the engineering. But you will not gain performance from your compounds being harder..

We offer Pre bedded race pads and rotors to our professional teams. but that's not an effort to sell harder pads. their track time is worth more than the extra $40 it costs to pre bed the pads and rotors. they can slap the equipment on and be racing or testing from the moment they leave the pits. normally on PFC it takes till the 3rd turn to bead in.