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Brake Knockback/Brake Kit Question

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Old 04-13-2018, 11:08 PM
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TheSilverFox
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Default Brake Knockback/Brake Kit Question
Hoping for any input on brake pad knock back solutions. Tracking the car is really unsettling not having a consistent brake pedal. Have searched and there are a couple threads, replace master cylinder, rebuild calipers or just replace system with brake kit. Most threads end with no definitive solution.

Looking for any real world input from actual solutions. Have seen a couple of Stoptech kits come up for sale but not much feedback and zero on Brembo system.

https://rennlist.com/forums/997-gt2-...e-track-2.html

https://rennlist.com/forums/997-gt2-...brake-kit.html
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Old 04-14-2018, 02:52 AM
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Spyerx
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How old are your hubs and bearings?
i get zero noticeable knock on my car
i use Brembo 380mm type5 hd rotors, full floating with aluminum hats, stock calipers that are refreshed regularly and reaches tecqhnology pads.
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Old 04-14-2018, 09:18 AM
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TheSilverFox
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Originally Posted by Spyerx
How old are your hubs and bearings?
i get zero noticeable knock on my car
i use Brembo 380mm type5 hd rotors, full floating with aluminum hats, stock calipers that are refreshed regularly and reaches tecqhnology pads.
Hubs were replaced last summer as didn’t know last time they were done. Didn’t change braking characteristics.
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Old 04-14-2018, 11:02 AM
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nwGTS
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Tom, GT3s have a brake priming feature where the car moves the brakes to the rotor surface when the accelerator pedal is lifted abruptly from WOT. So knockback should not be an issue on these cars if everything is operating correctly. I'd have your brake system inspected to be sure everything is working properly. The biggest question is if you are sure the problem is knockback. Could be rotor/pad material combo, rebedding needed, different fluid, sticking pistons etc.
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Old 04-14-2018, 01:37 PM
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Default Endless RF 650 fluid flush
Originally Posted by nwGTS
Could be rotor/pad material combo, rebedding needed, different fluid, sticking pistons etc.
This^^

First try flushing your brake system with Endless RF650 brake fluid.....this WILL give you a more consistent pedal when things get very hot at the track.

Best regards,
Doug N
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Old 04-14-2018, 02:37 PM
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TheSilverFox
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Originally Posted by nwGTS
Tom, GT3s have a brake priming feature where the car moves the brakes to the rotor surface when the accelerator pedal is lifted abruptly from WOT. So knockback should not be an issue on these cars if everything is operating correctly. I'd have your brake system inspected to be sure everything is working properly. The biggest question is if you are sure the problem is knockback. Could be rotor/pad material combo, rebedding needed, different fluid, sticking pistons etc.
Thanks, brakes were inspected when the hubs were replaced. Didn't see anything wrong but sticking pistons/seals would be obvious fixes. When the brake pedal is tapped before full braking they feel feel fine, but does add another level of drama to corners and not confidence inspiring. Spoke to two other Rennlisters that had similar issue and final solution was to replace the calipers with aftermarket. This was after replacing master cylinder, complete bleed, new rotors and pads.

You may remember that last corner at Autobahn last summer when I ran up your tail into the corner. That was when I called it quits for the day, way too much drama.
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Old 04-14-2018, 02:39 PM
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Originally Posted by DJN
This^^

First try flushing your brake system with Endless RF650 brake fluid.....this WILL give you a more consistent pedal when things get very hot at the track.

Best regards,
Doug N
Thanks, will give it a shot. Cheap and easy option either way.
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Old 04-15-2018, 10:09 AM
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nwGTS
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Originally Posted by TheSilverFox
You may remember that last corner at Autobahn last summer when I ran up your tail into the corner. That was when I called it quits for the day, way too much drama.
Its why I bring an extra set of underwear to every track day now.
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Old 04-16-2018, 12:12 PM
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Can you describe in more detail what you are experiencing? What tires do you run, and what brake fluid / pads / rotors? Also can you describe your braking profile. And, what is your alignment, specifically rake? Lastly, what diff do you have?
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Old 04-16-2018, 07:25 PM
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TheSilverFox
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Originally Posted by Spyerx
Can you describe in more detail what you are experiencing? What tires do you run, and what brake fluid / pads / rotors? Also can you describe your braking profile. And, what is your alignment, specifically rake? Lastly, what diff do you have?
When I first touch brakes coming into corner the brake pedal is very long and stopping power isn’t there. Tap the brakes once and then get on them and they are fine. Still leads to somewhat inconsistent braking. Below is from another thread, describes it perfectly

recap the original problem, the brake pedal would start to get "long" on the track. As the brakes got hot, it took more pedal travel to get braking as a track session progressed. A quick tap on the brakes before hard braking would temporarily restore the brakes to normal, so that became my braking routine on the track.

Tires - Michelin Super Sport & currently Michelin 4s
Fluid - Castrol SRF
Pads - Pagid and currently Performance Friction 08 or 11 can’t remember which in file at home
Rotors - AP racing
Alignment would need to check file
Differential was rebuilt by previous owners shop less than 10k ago
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Old 04-16-2018, 10:04 PM
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To me that sounds exactly like overheated brakes and not knock back.
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Old 04-17-2018, 07:42 AM
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TheSilverFox
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Originally Posted by nwGTS
To me that sounds exactly like overheated brakes and not knock back.
Would agree but the symptom begins on the outlap. Will try different fluid, Endless seems to be a popular choice.
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Old 04-17-2018, 01:22 PM
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grrrmonster
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Had similar issue. Rebuilt calipers, replaced brake lines, replaced master cylinder, replaced front hubs. Still have same symptoms. I gave up
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Old 04-17-2018, 02:42 PM
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nwGTS
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Does anyone think he may be falling victim to ABS Ice Mode? Tom, are you familiar with this?

General thread:
https://rennlist.com/forums/997-gt2-...ly-got-me.html

One of the better posts (#293) from that thread:
https://rennlist.com/forums/997-gt2-...l#post14192855
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Old 04-17-2018, 07:03 PM
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Originally Posted by nwGTS
Does anyone think he may be falling victim to ABS Ice Mode? Tom, are you familiar with this?

General thread:
https://rennlist.com/forums/997-gt2-...ly-got-me.html

One of the better posts (#293) from that thread:
https://rennlist.com/forums/997-gt2-...l#post14192855
Yes I did run across this, this symptom only seems to be in certain situations. The GT3 symptoms are every braking zone. Turn 1 and 5 at Road America are quite the event at +160 mph.
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