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Brake pad knockback

Old 05-21-2018, 06:41 PM
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Originally Posted by Blkbrd69 View Post
Have you ever watched a video of a top sedan racer racing an older car where they had to use all the peddles all the time? Its amazing watching them left foot set pads before braking zone prior to beginning threshold braking with right foot.
I've done a lot of this.

The problem is flex in the upright/hub assembly causing the rotors to push against the pads and subsequently push the pistons back in to the calipers. Typically worst in high-G back and forth complex sections. Floating rotors eliminate the knock-back. It's a reactionary solution, I'd prefer to eliminate the flex that is the root cause, but at least at this point in the development of fast Miatas, we don't have that solution yet. Floating rotors are a solution. Regarding floating rotors, how much float you need depends on lateral grip and specific track. Stoptech has a Street and Race version of the floating hardware. The Street has solved 99% of the knockback in my car for all of the SoCal tracks I frequent. At VIR I had substantial knock-back, first time since changing to floating rotors. Possibly because that track has way more complexes with lots of load than most, including the "esses" which I was doing 135mph through. On my dry laps I was pre-loading the pistons with my left foot before every braking zone, and elsewhere just to reassure myself they were still there. Looks like I need the race version at that track.

As a result of my testing, we sell the floating version of the ST kit because that's what works. Street floating version by default, Race by request.

I haven't tested the Ken Auto brace, but I'm skeptical.
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Old 06-06-2018, 12:17 AM
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I too have been chasing pad knock back ever since I installed my TSE dynapro kit. Glad to hear its not just me. Anyone else having issues with slightly funky pad wear? I think the calipers need the bridge bolt that FM sells. https://www.flyinmiata.com/dynapro-bridge-bolt.html
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Old 06-06-2018, 02:27 AM
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I get tapered wear with the dynapros, but no knockback.

The bridge bolt might help a bit, but I wouldn't expect miracles from it.

--Ian
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Old 06-06-2018, 03:39 AM
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Its not that bad. Only slightly tapered but enough for me to care. FM says 10% increase in stiffness which should be enough to take care of most of the problem I think. Its only $30 for the kit so whatever. The flip side is with how much im tracking the car, im thinking of doing superlites on custom full float rotors. Or an AP racing caliper of some sort. This will allow more pad without the knocked issue. We are working on a potential kit now.






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Old 06-06-2018, 08:56 AM
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I haven't worn out a set of pads with my setup working properly, but the set that ate **** in quick fashion were tapered/uneven as well. Hopefully i'll get enough driving in this year to wear the PFCs to see if they're tapering or not. I just added bridge bolts and went to the HD rotors in my car.
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Old 06-06-2018, 07:38 PM
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im runnig PFC 11s for what its worth. This is my 2nd set.
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Old 06-06-2018, 07:43 PM
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I have 01s, which i think are same, or close enough to 11s.

The set that ate **** were not PFCs.
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Old 06-07-2018, 12:06 AM
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I think im gonna go back to G-LOCs. Ive gone through 2 sets of PFCs in 9 months.
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Old 06-07-2018, 12:14 PM
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Originally Posted by MiataMan00 View Post
I think im gonna go back to G-LOCs. Ive gone through 2 sets of PFCs in 9 months.
Stock brakes? Ducting?
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Old 06-07-2018, 12:25 PM
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With a good driver in a fast car, you can only expect to get 3 days or so from a set of 12mm pads. Maybe 4-5 days from 16mm pads. 6-7 days from 20mm Superlite pads is the norm.
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Originally Posted by codrus View Post
Basically I've come over to the camp of "If something is a reliability problem on the track, just ask Andrew and do what he says".
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Old 06-14-2018, 04:14 PM
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Old 06-14-2018, 04:24 PM
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I just saw a discussion about that valve on another forum yesterday. Apparently it's frequently used by honda road racers who have problems with knockback caused by flex from weak hubs and knuckles. Supposedly works pretty well. Should have basically the same effect as the knockback springs that AP Racing and some of the other high end calipers have built in. I'm trying to get my friend to try it on his V8 car.
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Old 06-14-2018, 06:38 PM
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Originally Posted by sixshooter View Post
Stock brakes? Ducting?
TSE Dynapro kit, 3" Singular ducts
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Old 06-25-2018, 11:46 PM
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When is the last time the calipers were rebuilt? I fought knock back for a while on a different car and it went away when i rebuilt the calipers with new seals and pistons. Sticky pistons on old seals make the problem worse. I also added anti knock back springs behind the pistons.The springs are made by Brembo and I got them from Hoerr Racing Products.
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Old 06-26-2018, 12:57 AM
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Originally Posted by ThePass View Post
The problem is flex in the upright/hub assembly causing the rotors to push against the pads and subsequently push the pistons back in to the calipers. Typically worst in high-G back and forth complex sections. Floating rotors eliminate the knock-back. It's a reactionary solution, I'd prefer to eliminate the flex that is the root cause, but at least at this point in the development of fast Miatas, we don't have that solution yet. Floating rotors are a solution. Regarding floating rotors, how much float you need depends on lateral grip and specific track. Stoptech has a Street and Race version of the floating hardware. The Street has solved 99% of the knockback in my car for all of the SoCal tracks I frequent. At VIR I had substantial knock-back, first time since changing to floating rotors. Possibly because that track has way more complexes with lots of load than most, including the "esses" which I was doing 135mph through. On my dry laps I was pre-loading the pistons with my left foot before every braking zone, and elsewhere just to reassure myself they were still there. Looks like I need the race version at that track.
Update - back on Rivals at WSIR and therefore less lateral load (about the same as most non-aero cars on A7s), only a very minor hint of knockback after T2. This is still with the "street" floating hardware.
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Old 06-30-2018, 12:25 PM
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Thanks to all for the great feedback and insight. Having a better understanding of the problem I now understand why it shows up when it does. I am able to drive around it for the most part but a solid pedal would help me with that last few seconds left on the table.

I am tempted to try the 11” stop floaters but I’ll likely wait for V8R to release their upcoming 11.75 floater kit. I got a lot of rear bias now and going to 11” kit won’t help that. I am also tickled pink with pad life on the 11.75/Cobalt/Stoptech setup so I’d hate to go backwards there. I think shimming pads pads as they wear will help as it keeps the pistons in the bore. I may even try the knockback springs. I would love to know how much drag they have though. The hydraulic solution looks intriguing too.
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