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Discussion Starter · #1 ·
OK, recent DE at Laguna with my (base) Cayman.. . I routinely swap OEM brakes from daily driving for Pagid Orange pads for D3.. this time the Pagids were brand new.
After a couple runs, when trying to "trail brake" or brake into a turn (yes, I know I should complete braking in a straight line... more later)... as in going into turn 3, turn 6, turn 9 ... as the car loads one side, the pedal throbs -- not like anti lock starting to work -- but close to it.
Straight line braking, as into turn 11 was flawless and impressive.

My question -- anyone hazard a guess what might be causing this pulsating when the car is turning (even slightly) with brakes applied??

As the day wore on, I simply only braked in a straight line, getting off the brake pedal before ANY turn in... yes, this was equal or faster ... but still, the braking was unsettling??

Any thoughts on why this felt this way, maybe traction control not functioning correctly (I didn't have the courage to turn PSM off), or ??


Don
 

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New brake pads must first be bedded in. Until then you cant expect full performance nor should you attempt to use them to the limit.
It sounds very much like you have warped rotors or the pads are not bedded properly.

Correct bedding for PCCB takes about 500kms of street driving.
 

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First, trail braking is generally faster, depending on the corner if done properly, but I am not familiar with LS to really have an opinion on the turns you mention.

I trail brake as often as I can as I became more accustomed to the CS' dynamics. I do not turn off PSM, it is always on in sport mode. If I am too aggressive on the brake while trail braking then ABS will intervene, I believe this to be normal as the inside tires unloads and its grip lessens and it will come close to lock up or will lock up; so ABS is probably doing its job right. As we learned, you cannot have 100% of all forces at the same time in all directions. So, while trailing the brakes in a turn, you have to lessen the brake pressure.

Since your brakes seem to be working just fine in a straight line, I doubt there is an issue with pad/rotor bedding, you may want to experiment with changing your driving style during trail braking.
 

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Discussion Starter · #6 ·
I'd bet on PSM, but it will also make the car and pedal shudder under braking if your rotors are somewhat warped. Happened to me last week.
Thanks for the ideas.. warped rotors huh??
Question... would swapping OEM pads for Pagids for each DE help to warp the rotors?? or>>. maybe I ran the old set of pagids too far down and that warpped the rotors??

Would a dealer or speciality shop be better to evaluate the rotors ... or must you evaluate at speed??

Last question -- I'm thinking its the fronts --- just because of the feel... when you replace rotors, do you do front and rear or just fronts, for example.

Thanks again for everyone's thoughts.
Don
 

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You should be able to feel warped rotors with straight line braking especially when light braking.

I'd go with PSM, and whilst the light was not coming on it is likely it was still working.

Because you were trail braking it's posible PSM thought that the g's at entry made it think you were going to over-rotate and so PSM thought it would bring it back in line.

Driving with PSM off is the best way of keeping your brake temps down, however if you have good lines it shouldn't kick in too much.....however you push too far and you'd better be ready! One month back at Yas Marina I had the CS at maybe 70 degrees when I put the power on a little too soon with PSM off.

As said by others trail braking is the fastest way around the track.
 

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"Warped" rotors are very unlikely on our cars - the sensation of uneven braking (at slower speeds, in a straight line) is more likely due to uneven pad deposition on the rotor.

I agree with those above that you may have been feeling the PSM kick in if you were close to the limit while trail-braking.
 

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Discussion Starter · #10 ·
OK... down to maybe not wrapped rotors... and maybe PSM kicking in...
though I felt that the sensation was way more pronounced this DE than last time (last time was at Thunderhill.. had similar but less pronounced sensations going into a couple of their turns...

I'm still wondering how would I troubleshoot either possibility --- I mean, one way is just to bolt on a couple new rotors on the front... a bit pricey, but not outrageous... but that seems to be a bit arbitrary right now.

Any more thoughts?? Anyone have the same "sensation" while at speed at DE's ?? OH yea, remember my car is a base Cayman, so the rotors are a bit thinner than the more beefy CS rotors.

thanks again. Don
 

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I am not sure what 'warping rotors' mean. If we are talking about uneven pad deposits on the rotors, that is easy to take care of by just driving around with different pads and it will just clean it up in few hours of drive, just normal driving.

Since your braking is fine on a straight line, just experiment with differing ways of trail braking before you change brakes, rotors, pads, lines, etc.that is the cheapest thing you can try. Another thing you can try is have an instructor drive it for few laps and see if he senses weird operation.
 

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Discussion Starter · #12 ·
One more recollection about my experiences... the pulsations upon braking was worse as the day wore on -- or -- as the brakes got hot. The initial session was unremarkable...

The question about techniques for trail braking aside -- I just don't think there should be such pulsations felt on the pedal (or even lock up -- I couldn't tell about that...) while trail braking... especially in light of my recollection that the later runs seemed to be worse...

Again, any thoughts on how to analyze this -- other than going back on the track -( I can't see trying to induce on the street -- way too dangerous on local roads and way too fast for local limits...).
Thanks in advance.
Don
 

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I agree with the "not warped" rotor responses. It takes tremendous heat to get a cast iron rotor to warp. Plus, if the rotors wear warped, to effects would be felt during all brake applications. Most likely cause for shutter (under any brake conditions) is pad transfer to the rotor.
 

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Discussion Starter · #14 ·
Yep.. pad transfer is the consensus..
Now a question... Is there a way to "remove" old pad materials that are on a rotor, other than putting the rotor on a metal lathe and turning it down a bit.. I'm thinking whether it is possible -- or advisable -- to use 1500 grit emery paper or something and "sand" off old material before mounting a new pad -- or in my case, between swapping out OEM pads with Pagid pads for DE's ?? then do a proper job of bedding in the "new" or "remounted" pads. Sounds kinda hokiee... Or is there a better way??

Thanks in advance ... D
 

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You really do not need to do anything other than drive the car for few days and normal braking will clean the rotors regardless of pads you have on. Then, the important part is to fully bed-in your track pads before track session.

I had this issue several times before, especially when switching between track compounds and did not have time to bed-in the new compound. When that happens, I drive for few miles on the road outside of the track between session to clean the rotors, and bed-in the new pads and voila...
 
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