How Should Carbotechs Feel When Hot?
 

I run the 11" Wilwoods with XP10 front and XP8 rear. I was out lapping today, and it was hot . . . like 104 ambient hot.

In the biggest braking corner (100mph to 40mph), after several laps the brakes felt/sounded somewhat metallic/crunchy. It still stopped OK and the pedal was stiff, but the feel/noise was kind of strange.

Post track day inspection did not reveal anything unusual on the discs or pads . . . they look fine. They also feel fine in normal driving.

Is that just how the Carbotechs feel when hot? Or maybe I have something else going on like a rear wheel bearing? Mainly noticed upon brake application at higher speed (~100).

A metallic squeal is pretty normal in my experience, but I can't say that I've experienced the crunchiness that you're describing. I have experienced what I'd describe as a gritty, sand-papering feel, but that's mostly when cold, and it smooths out once they are hot. This is just from what I recall from last season, I'm on DTC-60s now.

I'd expect the post inspection to tell the tale if something was amiss though..

-Ryan

Gritty/sand-papery pretty much describes the feeling. Seemed to be coming from the rear. Didn't happen until things were nice and warmed up, so opposite of what you experienced.

Going to change fluid in the diff. Is there a good way to inspect rear wheel bearings without taking everything apart?

Grab the wheel at 12-6 and again at 10-4 and shake back and forth. If you hear a thud-thud. Then your wheel bearing is out of whack, and in need of replacement. You can also pull everything off and put a dial indicator on your hub. Check it for lateral run out. lateral run out on a hub (caused by a bad bearing) will give you lots of brake drag, and exponentially shorten your rotor and pad life. My reports from Spec miata teams the hub is a fairly normal item to fail on a track miata.

Noise is fairly normal in application but the grinding feeling isn't. What's your application? (car & hp). What track where you running, and at what turn where you having the issue at? maybe we can get into this and figure it out.

It's my red car. 1995 Miata normally aspirated (~135-140RWHP) with Xidas, poly bushings and 15x9 + 225 Rivals. Track was MSR-Cresson 1.7CCW and it was the big brake zone going into the Rattlesnake complex (slowing from 100 to 40mph).

I've also experienced the gritty feeling with Carbotech pads, also in a high temp, large decel situation (130mph - 55 mph). I think how well the pads/rotors are bedded can affect the severity of the issue. That is, I've had some Carbotech pads not do it at all, and another set do it quite a bit.

As far as I could tell, it had no affect on braking performance...just didn't feel great.

Yeah, I bedded these per the Carbotech instructions the morning of the track day. But I had been street-driving them for a few days before that while I broke in the engine. I wonder if I f***ed up the pads? I hope not. At least the feel from the front is good.

I've gotten the grindy feeling with my old pads. It ultimately had no effect on performance, pad life or rotor life. Just sounded not great and felt gritty... basically echo what Efini said.

allot of the hawk, carbotechs, you can lose the bedding. sometimes if there is contamination on the rotor it's almost impossible the pad in. I had some dtc60's when I installed the Goodwin bbk. I left the "L" and "R" stickers on the rotors and decided the pads would remove them. that never happened. the contamination from the sticker glue just stuck. I had to change pads before I could get them bedded in properly.

Never experienced the "gritty" feel under braking with Carbotechs. Pulse from deposition a few times but no grit or grinding. I've gone through maybe 50+ sets of Carbotechs in maybe 6 different cars in maybe 500+hrs over the last 8 years so, a decent size data set.

Thanks for the feedback all. I'm going to give the car another hard look. If anything else turns up, I'll post it.

Couple of Pictures
 

Front (XP10):
https://www.miataturbo.net/attachmen...1&d=1407794941

Rear (XP8):
https://www.miataturbo.net/attachmen...1&d=1407794941

I think the disc bedding looks OK. Thoughts?

Never mind the grass by the way :giggle:.

never experienced that. I will say my carbotech XP8s where not really up to the task of dealing with CMP when I swapped over to 205 NT-01s. That is near the same grip as you...

I know the range is up to 1200, but I went through my front set in ~2 weekends and what pad was left was actually breaking off. My rears experienced more wear than I have seen before, but didn't notice anything too odd there. Wondering if maybe your pads did something similar in the rear...

I would suggest you move up to a more serious pad in the rear.

What Emilio calls "pulse from a deposition" could be what others are calling "grainy".

My most recent experience with "grainy" feeling of carbotech pads was on an S2000, XP24s front, xp12s rear so my experience may not translate. I raced a civic on the exact same day, with the exact same compounds and didn't experience the "grainy" feeling.

I think the fact you drove the pads on the street a bit before properly bedding them may be part of the issue. In my experience Carbotechs are more sensitive to proper bedding procedure than other pads.

Hard to tell, would need a close-up of the rotor, but the fronts on your farm tractor look like they have some pad deposits on them, which could be related to the feel you're getting.

-Ryan

I definitely had pad deposits on the front coming off track at the hottest part of the day. Now that I've street driven a couple of days, they've disappeared. What's wierd is that the fronts felt OK and the gritty sound/feel seemed to come from the rear -- which didn't exhibit any splotchiness.

Related is that the rotors are the standard Wilwood castings and the fronts are getting close to their limit (I measured ~0.78", limit for these is 0.75"). It may be that I need Emilio's improved casting or just convert to the 11.75" rotors for the cost advantage.

Plan to get the car up on jackstands tonight for a more thorough investigation and better pictures.

I can tell that the transfer layer is not consistent. you can clearly see rings where the transfer layer is gone. I do agree with ryan, are these your track/field plowing tires?

At least my furrows are straight.

I was trying to keep it flat-out down "Ricochet." It's taken a bit of time to build up the nerve. I was approximately 70% successful. :party:

My take on "metallic/crunchy" of the OP and "grainy" "gritty" vs pulsation.

Deposition will usually cause a pulsing that feels almost exactly like a warped rotor. Not rough. Just the braking grabbing and releasing as if the rotor was warped or almost like a flat spotted tire.

The metallic/crunchy, gritty, grainy I have never noticed with Carbotechs. I would equate that to a high metal content pad like a hawk blue that isn't hot enough or like worn pads that are metal backing plate to rotor grinding.

Two distinctly different feels to this driver.

"Might" Have Found Something
 

I was doing some further inspection of the rear brakes and found something that might explain what I felt. I've got the old V1 Goodwin BBK installed on the car. This was installed by the PO and all I've done is basic maintenance (pad changes, lubricate pins, fluid flushing, etc.).

Looking closely at the allen-head pan bolts that secure the friction ring, they have almost no clearance to the caliper bracket. A close up of the bolt head shows that it looks like it's been hit with a file. Pics:
https://www.miataturbo.net/attachmen...1&d=1408045302

https://www.miataturbo.net/attachmen...1&d=1408045302

https://www.miataturbo.net/attachmen...1&d=1408045302

Here's a reference photo I found on FM's website showing how that bolt looks when new:
https://www.miataturbo.net/attachmen...1&d=1408045302

I'm going to do some more teardown tonight to inspect the brackets for matching interference marks. Theory could be that when sufficient brake torque is applied, the brackets might bend sufficiently to contact those bolt heads?

Anybody ever heard of this? Perhaps I'm missing a spacer that should be used with this BBK?

I dunno.

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.

Are you saying that with pre-bedded pads, I can take new rotors and new (pre-bedded) pads, put them on and go, without any worry at all?

robert

yea you can.. i was at the plant where they did it (Clover, South carolina). One Poor bastard sits on a brake dyno and spends all day beading in pads and rotors. then sends them off to nascar teams..

IMO if you buy a good quality pad and good quality rotor they will bead in with no problem. i had Good wins kit and hawk pads. couldn't get a transfer layer to save my butt. too many contaminants in the pads and rotors. switched over to PFC 01 and PFC rotors on trackspeeds 11.75" kit.. i haven't had the problem since.

No, he said they offer pre-bedded pads AND rotors i.e. a bedded set that have been worked as a pair.

You can buy pre-bedded pads straight from Carbotech but you still need to get a good transfer layer on the rotors before going hog wild on them.

A pre-bedded set of pads AND rotors doesn't require that. You can pull them straight out of the packaging, put them on the race car and do a 2.5 hour race.

A lot of pro teams do this because, as OG mentioned, track time is so limited (and expensive) that you don't have time to bed brakes and "scrub" tires, etc etc

^exactly. To get the combo You need to be running a PRO style race caliper. PFC doesn't have any wilwood dynalights or miata calipers to bolt to the dyno.

Most of us run the Wilwoods or OEM calipers. I would have been interested in pre-bedded pads + rotors, but it sounds like it would not have been available anyway. ??

For those that already have healthy rotors with a transfer layer, yes you can slap prebed Carbotechs and race right out of the box. We do this all the time. One session of track time will always more than the $20 fee to prebed.

It's throwing cash away for a club racer.. for a pro team each lap could cost 100 bucks if you add in travel, Crew pay, Track rental (remember they rent the entire track for one car). If you have a Good rotor and High quality pad you won't have any issues with keeping or getting a transfer layer.

^that's not it. if you're making contact there would be marks on the bolt heads. i don't see any marks.