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.