k24madness

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matrussell122

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I just went to the 11.75 BBK and dynapro calipers and I have pad knock now. Dont know what is causing it but i just accepted it as how things are.The only way i thing to properly fix it is with pad shims like on a lot of oem cars.

k24madness

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matrussell122

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Which axis do you think you knock is occurring? I was referring to the rotational forward/backward movement that would cause knock.

Disclaimer:
I am an idiot and know some things about a lot of things

acedeuce802

iTrader: (1)

Knockback refers to the rotor pushing the piston back in the caliper. Basically upright/hub flexes under cornering load, rotor moves in relation to caliper, pushed piston back in. Then the next time you hit the brakes there is extra pedal travel before the pad touches the rotor. This is why calipers are not mounted on the top or bottom of the rotor (they are near 90 or 270 degrees, or at least close) because that would magnify the issue. This is not a "knock" noise.

I don't have enough time on my 11.75" kit to comment on knockback. But, this is certainly an issue that's magnified by fixed rotors and fixed calipers. What tires do you run, and do you have any aero? Miata uprights aren't the stiffest out there, so it could just be a sticky tire, high load, flexy upright, some hub flex (normal, not saying bad hub), and fixed/fixed brakes. If no one else has this issue, then I'm not sure what's different about yours. It's good practice on long straights anyway to lightly tap your brakes before you let off and actually brake. Just enough to feel that the pads are there, and this would bring them back in contact. More of a bandaid fix for knockback, but if the root cause is a flexy upright/hub then there's not a whole lot you can do.

matrussell122

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Copy that i read it as pad knock. Pad knock would be rotational knock correct? sorry if its a dumb question.

acedeuce802

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Pads can rattle axially, or knock radially. It's just completely different since you're talking about a knocking noise, whereas k24 is talking about the pads getting knocked back in the caliper. But yes, the pads are essentially floating, and if there's too much clearance radially between the "ears" of the pad and the caliper, then it can make a noise when you load up the pads.

k24madness

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matrussell122

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Im all up to speed now. Thanks for the clarification. My derailment of the thread has now ended

jpreston

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A local V8 miata is having really bad problems with hub/upright flex right now. Running the V8R 11.75 Stoptech kit with 275 hoosiers on the front. He had the car out a week or two ago and the flex was so bad that the rotor was rubbing on the steel stoptech pad retainers during cornering and wore a groove into the rotor face.

sixshooter

iTrader: (12)

I talked to the owner of a former trans-am series c5 vette with ridiculously wide slicks at Sebring. With the grip, tight springs, and uneven surface of that track he said he needed two full strokes of the brake pedal to get the pads to engage in most corners due to knock back from spindle flex. Sounded scary.

I've seen a device to help this issue on some Miata related vendor site recently.

acedeuce802

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sixshooter

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I found the device.

brace

No reviews yet but if you are having problems it's not a huge amount of money to solve or help if it works.

jedd

On my spec miata I run all the factory springs(or the thickest aftermarket ones i can find) on my brake pads and gutted the emergency brake mechanism in the rear caliper to increase knockback. Its real bad after rumble strips but I will take the decreased rolling resistance all day. A quick brush of the pedal with my left foot before braking zones is enough to build the pedal back up, careful not to push hard enough to physically feel any loss of speed though.

Blkbrd69

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.
At Sebring in my C6Z I had to learn, otherwise ran out of brake before turn 7. Huge Stoptechs fixed that issue.

k24madness

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Midtenn

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I was thinking about these as well, but couldn't remember who was selling them. Curious if anyone at Goodwin has tested them out.

k24madness

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Savington

iTrader: (31)

Those braces will do absolutely nothing to assist with knockback. Knockback is the rotor moving independently of the caliper, so the stub axle has to flex in relation to the caliper mounting tabs. Even if that does stiffen the spindle (I am highly doubtful that it does), it stiffens the spindle behind the caliper tabs, leaving the stub axle to flex.

acedeuce802

iTrader: (1)

This is my thought too. At the ball joints, the cornering forces are already reacted in tension/compression by the control arms, so the flex that is already there between the spindle and upright is still going to be there if the ball joints are constrained vertically. It may make a difference, but it's not addressing the main lack of stiffness that causes knockback, so I doubt it'd be night and day difference.