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Discussion Starter #1
Hey all,

So I did my second track day yesterday (sunday) at the Streets of Willow, and it was awesome. However the awesomeness was cut short two and a half sessions early due to a braking issue i was having. here goes.

Coming up the main straight, was at about 120/125 ish, and for turn one, i had to brake down to around 85 ish (if i was pushing it... i'm slow, i know.) At that point, the braking went fine. However, after the fast turn 1, you have to brake decently hard for turn 2, adn that's where things got wonky. The brakes produced a massive vibration going down from 85 to about 40 ish before entering the turn. At the two high speed spots on the track, it did this. However, the vibration occurred under intense braking, only if intense braking had recently occurred. At my last attempt to replicate the situation, i held the brake longer, the vibration got considerably worse, and then the brakes lost feeling. All of this leads me to believe that i overheated the components, nullifying their effects. Needless to say, i would like to get this remedied before i go to the track next. I'll rephrase. I'm not going back to the track until this gets cleared up. no need to hurt myself or anyone else out there.


Do any of you have insights as to what this could be? Another issue is that given speed laws, i can't safely attempt to recreate the situation until i go back to the track. Of course i'm going to have my local shop look at it, but my mechanic is convinced that there's no way i could have overheated my OEM brakes and rotors. By the way, it's a 2006 ZX6R (636) with stock everything, with the exception of the steel braided brake lines.


Any insights are helpful, guys!

Thanks, everyone!

-J
 

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Too mutch rebound damping in my ears. Check your settings. I'm not a guru so I'm not 100% though.

-under hard braking, you compress the fork, too much rebound makes it too slow to stretch out again in the turn where you compress it again - now you don't have a lot of suspension travel left, and before the fork can expand again you brake - you are now out of suspension travel and the front is stiff bottomed out. Every little grain on the asphalt is felt through the bars.
 

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If once it started doing it, it did it consistently then I would say you warped a rotor. Not uncommon to occur and its fairly cheap and easy to fix.
 
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Discussion Starter #4
Too mutch rebound damping in my ears. Check your settings. I'm not a guru so I'm not 100% though.
In my suspension? It didn't feel like a bounce, it felt like a vibration. The exact same thing used to happen when i towed my sea doos (with my SUV, not the bike, ha!) coming back from laughlin down the el cajon pass (steep downhill, for those of you not from here). I got a massive vibration in the pedal after extended periods of riding the brakes. That's what this was. However it filtered into the bars.

I'll have the suspension looked at though, thanks for the input!

Thanks,

-J
 

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In my suspension? It didn't feel like a bounce, it felt like a vibration. The exact same thing used to happen when i towed my sea doos (with my SUV, not the bike, ha!) coming back from laughlin down the el cajon pass (steep downhill, for those of you not from here). I got a massive vibration in the pedal after extended periods of riding the brakes. That's what this was. However it filtered into the bars.



I'll have the suspension looked at though, thanks for the input!



Thanks,



-J

I added a bit for you to see how I think. Since it's not consistent, the rotors should be fine.
The track is a perfect place for testing - no trees, rocks, guardrails or cars going the wrong way if you crash.
 

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Discussion Starter #6
I added a bit for you to see how I think. Since it's not consistent, the rotors should be fine.
The track is a perfect place for testing - no trees, rocks, guardrails or cars going the wrong way if you crash.

That's an interesting point, i hadn't looked at it that way. And you are right, the track is a perfect place to test it. The problem is fixing the issue once i get there. I'd rather get it fixed before hand. But that may not be in the cards. I'll start by replacing pads. Those are probably running low anyway.
 

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loose steering stem? Honestly, if it's your first track day, the chances of you warping rotors (unless theyre cheap ebay crap) or over heating any components on an otherwise well mechanically sorted machine, is doubtful. Maybe suspension, but really, I'd be looking for something mechanically that failed, not a suspension adjustment (unless something in the suspension broke)
-Cody
 

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Whats the maintenance history with your bike? when was the last time you changed your brake fluid? last time you replaced the fork fluid?

Start with brake pads first and replace the brake fluid as well. im leading towards rotors but start with the simple stuff first. is this a dedicated track bike or a double duty street bike?
 

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Maintenance history is pretty solid. Brake fluid was replaced in september, with minimal riding in between, the bike is an '06, it has under 13k miles on it. Couldn't tell you when the suspension fluid was replaced, or if it was replaced. The brake fluid is going to be replaced very soon. It's a double duty bike, but as you can tell, it doesn't get much miles. I've owned it since 09, and it had 5400 miles on it when i bought it. So it doesn't get much use. I can't find time. But i'm not on here to tell my sob stories, haha.

I do not live in san diego. Bummer.
 

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Maintenance history is pretty solid. Brake fluid was replaced in september, with minimal riding in between, the bike is an '06, it has under 13k miles on it. Couldn't tell you when the suspension fluid was replaced, or if it was replaced. The brake fluid is going to be replaced very soon. It's a double duty bike, but as you can tell, it doesn't get much miles. I've owned it since 09, and it had 5400 miles on it when i bought it. So it doesn't get much use. I can't find time. But i'm not on here to tell my sob stories, haha.

I do not live in san diego. Bummer.
probably consider changing your fork oil as well. For normal riding, it should be done every 2 years. For track and agressive riding, I usually only get about 10-12 months before I start to notice the front getting spongey.
 

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Thanks guys, i'll take a look into all of that. Fork oil should definitely be changed, then. And even if that's not the problem, it probably couldn't hurt.

Hitman123, I'm in the san fernando valley.
 

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Thanks guys, i'll take a look into all of that. Fork oil should definitely be changed, then. And even if that's not the problem, it probably couldn't hurt.

Hitman123, I'm in the san fernando valley.
Send me a PM with contact info. I'm usually free weekends in the mornings unless I'm riding.
 

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I had a similar problem, heavy brake vibration under hard braking that'd get worse the hotter the brakes got.

Was glazed rotors/pads. I sand blasted the rotors and switched to different pads and it was solved.
 

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OP, this is definitely under braking only? and you feel it through your lever? Assuming this is true, read on:

And I am beginning to lose faith in this forum by the people who are suggesting suspension changes for a brake pulsation...

Anyway, pulsation can only be caused by the mechanical components of the system. Fluid will not do it, although it is good to change it regularly anyway.

Given that this is your first track day I am going to go with a frozen/gummed up button on a rotor. Take them off, check for straightness against a flat edge, then thoroughly degrease and make sure that the rotor floats on the buttons. It would be a good idea to bead blast the braking surfaces at this time or if you do not have access to a blast cabinet, really aggressive with brake cleaner and scotchbrite.

Change the pads since you suspect they are ready anyway and put it back together.

If, when all is done this does not fix your issue, look to wheel bearings/head bearings.
 

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OP, this is definitely under braking only? and you feel it through your lever? Assuming this is true, read on:

And I am beginning to lose faith in this forum by the people who are suggesting suspension changes for a brake pulsation...

Anyway, pulsation can only be caused by the mechanical components of the system. Fluid will not do it, although it is good to change it regularly anyway.

Given that this is your first track day I am going to go with a frozen/gummed up button on a rotor. Take them off, check for straightness against a flat edge, then thoroughly degrease and make sure that the rotor floats on the buttons. It would be a good idea to bead blast the braking surfaces at this time or if you do not have access to a blast cabinet, really aggressive with brake cleaner and scotchbrite.

Change the pads since you suspect they are ready anyway and put it back together.

If, when all is done this does not fix your issue, look to wheel bearings/head bearings.

"However, the vibration occurred under intense braking, only if intense braking had recently occurred."

Warped rotors becoming straight and staying straight until you brake hard 2 times in a row? Non concistent problems are mostly rider error in some way, not the bike. Also, described as vibration is not telling me that the brake lever is pulsating.

I missed this part though

"At my last attempt to replicate the situation, i held the brake longer, the vibration got considerably worse, and then the brakes lost feeling."

That would rather lead me to believe the fluid was boiling? At least if the vibration was in the brake lever. Needs to be in pretty bad shape for that to happen though.

Not saying you are wrong though, only that it is not the standard warped-rotors-symptoms.
 

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"However, the vibration occurred under intense braking, only if intense braking had recently occurred."

Warped rotors becoming straight and staying straight until you brake hard 2 times in a row? Non concistent problems are mostly rider error in some way, not the bike. Also, described as vibration is not telling me that the brake lever is pulsating.

I missed this part though

"At my last attempt to replicate the situation, i held the brake longer, the vibration got considerably worse, and then the brakes lost feeling."

That would rather lead me to believe the fluid was boiling? At least if the vibration was in the brake lever. Needs to be in pretty bad shape for that to happen though.

Not saying you are wrong though, only that it is not the standard warped-rotors-symptoms.
I see your point and it is valid however allow me to counter. This is *exactly* what will happen in a slightly warped or stuck button situation. I mean no disrespect to the OP but it would be unbelievably rare that a first time track rider is boiling brake fluid by dropping from 120 to ~80 mph. Unlikely in the extreme.

This will be elementary but please bear with me as this may not be common knowledge to all.

When the warped section of a rotor passes between the brake pads, the irregularity forces the brake pads further apart. This means that for a split-second the pads will lose contact with the rotor as brake pressure forces them back against the flat (true) part of the rotor. For that micro-second you lose braking power.

The faster we go, the more revolutions that the warped section passes between the pads, the more braking time we lose. At top speeds (120 would qualify) you are losing a significant amount of stopping time as the pads work to simply reconnect with the rotor surface before the warped section passes back through again, repeating the process.

As we should all know, heat causes metal to expand so as the rotors heat up, it will exacerbate the problem which is why the trouble might worsen the longer you stay on the binders.

Now, I am not saying that this IS the cause, only that in my opinion it is the most likely. It could just as easily be caused by irregularities in brake pad material or parts of the rotor are glazed which happens a lot on street riders bikes, but since the OP is going to have to take everything off to check it anyway and likely replace the pads the steps I detailed above should result in a trouble free braking process.

In a nutshell:
  1. Check rotors for true/out of round
  2. Check for floating buttons
  3. Recondition/resurface rotors
  4. Replace brake pads

I have been riding for 30 years, and the above process has fixed every single brake pulsation issue that I have ever come across.
 
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