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Old 07-12-2008, 05:30 PM   #1
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A question for the fast guys...

I have an '04 GSXR750 trackbike all set up with the good stuff. (Fork internals, penske etc.)
Lately (last couple of trackdays) when I get a lot of speed on a straight and then get on the brakes HARD for the next turn the front shudders hard.
Not like headshake, not like a warped rotor just a hard shudder until I let off and then reapply. That usually will make it stop but by then I'm having a conversation with the Lord about making the turn.
I have checked the steering head bearings, rotors, calipers, etc. everything is tight.
I have cleaned the rotors with scotchbrite, that seemed to help but not a complete remedy.
I changed brake pads and thought that was the cure but last weekend at Eagles Canyon it happened again. A couple of times.
If I don't get a really good drive and some serious speed or if I'm easy on the brakes it seems to be OK but if I need to do some hard braking, sheesh I'm gonna have to start wearing diapers.


Any thoughts?
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Old 07-12-2008, 05:33 PM   #2
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Old 07-12-2008, 05:36 PM   #3
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Quote:
Originally Posted by bumblebee View Post
I have an '04 GSXR750 trackbike all set up with the good stuff. (Fork internals, penske etc.)
Lately (last couple of trackdays) when I get a lot of speed on a straight and then get on the brakes HARD for the next turn the front shudders hard.
Not like headshake, not like a warped rotor just a hard shudder until I let off and then reapply. That usually will make it stop but by then I'm having a conversation with the Lord about making the turn.
I have checked the steering head bearings, rotors, calipers, etc. everything is tight.
I have cleaned the rotors with scotchbrite, that seemed to help but not a complete remedy.
I changed brake pads and thought that was the cure but last weekend at Eagles Canyon it happened again. A couple of times.
If I don't get a really good drive and some serious speed or if I'm easy on the brakes it seems to be OK but if I need to do some hard braking, sheesh I'm gonna have to start wearing diapers.


Any thoughts?

brake fluid getting hot and making the pads a little grabby?
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Old 07-12-2008, 05:52 PM   #4
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Could be hydraulic lock on the front suspension or you could be bottoming out. Check to see how much suspension you are using a zip tie around the fork works. If you are using too much travel you might want to check your oil level and oil weight.
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Old 07-12-2008, 05:54 PM   #5
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Recent (last couple of trackdays) tire change?
Ok I'm not fast, but it's a shot.
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Old 07-12-2008, 06:27 PM   #6
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what fork oil weight are most using?
and how hard is it to swap out?
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Old 07-12-2008, 06:57 PM   #7
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Very likely one or both rotors are slightly bent, rotor carriers are too loose, or you've got glazed pads.

Usually if you heat the fluid, that results in fade, not a shudder.

Scotch-Brite (better yet, bead blast) the rotors, get some new pads (sometimes you can sand them, but pads are cheap), and make sure the rotors are straight- problem is that most of the time, you can't tell by looking.

My best guess is that your rotors are warped, but try the cheaper solutions first that you already started.

1. Clean rotors (preferably bead blast) and check "floating" carriers
2. New pads
3. Change fluid/ bleed system
4. Check tire condition for unusual cupping

That's where I'd start anyhow.
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Old 07-12-2008, 07:02 PM   #8
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Charlie - I will almost guarantee you the problem is your rebound valves in the forks are closed (turned clockwise) too much and you are experiencing what is know as "packing".

Turn the rebound valves clockwise (IN) and count how many turns or clicks it takes to close them completely (be gentle when they close [hit bottom] or you will damage the seats - just close them till they touch - do not use force) - record this data.

Next turn them BACK OUT to where they were and continue to turn them OUT 2 more turns.

Go ride it and if the problem is gone (which I am pretty sure it will be) then we will talk about how to get them set where you need them.
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Old 07-12-2008, 07:03 PM   #9
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try raising the front or dropping the rear.

edit not a fast guy
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Old 07-12-2008, 07:07 PM   #10
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Thanks for the input.
To answer some of your suggestions,

I do have a zip tie on the front forks and it is not bottoming.
Same tire.
Forks were rebuilt last year using correct weight. (about 6 trackdays since rebuild).
I did scotchbrite them thoroughly.(Improvement but not completely gone).
I'm using new pads. (again improvement but it happens still).
As far as warped rotors, that would seem to be a factor all the time. When the bike is on stands I can spin the front and there is no drag.
No unusual wear pattern on tire.

I haven't tried changing fluid, maybe that would help.

One of your suggestions Tom raises another question.
You said my carriers might be loose. the bolts that attach them to the wheels are tight.
Is it possible the buttons are loose? How can that be fixed?
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Old 07-12-2008, 07:09 PM   #11
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Quote:
Originally Posted by Radar View Post
Charlie - I will almost guarantee you the problem is your rebound valves in the forks are closed (turned clockwise) too much and you are experiencing what is know as "packing".

Turn the rebound valves clockwise (IN) and count how many turns or clicks it takes to close them completely (be gentle when they close [hit bottom] or you will damage the seats - just close them till they touch - do not use force) - record this data.

Next turn them BACK OUT to where they were and continue to turn them OUT 2 more turns.

Go ride it and if the problem is gone (which I am pretty sure it will be) then we will talk about how to get them set where you need them.


Radar, thanks for the suggestion. I wondered whether a suspension adjustment might be the fix.
I will try this on my next trackday since the bike is not street legal and it would require tripleing the speed limit to test anyway. LOL
Thanks again.
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Old 07-12-2008, 07:15 PM   #12
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Quote:
Originally Posted by tomLSTD View Post
4. Check tire condition for unusual cupping

That's where I'd start anyhow.
+1
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Old 07-12-2008, 07:18 PM   #13
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Quote:
Originally Posted by bumblebee View Post
Radar, thanks for the suggestion. I wondered whether a suspension adjustment might be the fix.
I will try this on my next trackday since the bike is not street legal and it would require tripleing the speed limit to test anyway. LOL
Thanks again.
Let us know - I've been around this very problem on several of my buddies bikes - test ridden one of them ( it is very scary if it's what I think it is), and solved this long distance over the phone for another one. I suspect you are bottoming them out or very close when it is occuring, although they may appear to have travel left externally (exposed chrome) they are probably out of travel.
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Old 07-12-2008, 07:18 PM   #14
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Quote:
Originally Posted by bumblebee View Post

One of your suggestions Tom raises another question.
You said my carriers might be loose. the bolts that attach them to the wheels are tight.
Is it possible the buttons are loose? How can that be fixed?
Yes, not the bolts that bolt the carriers to the hub, but the "floating" spacers and clips for too much play. Doubtful, but maybe.

Also, you're not likely to see a slight warp in one or both rotors by looking for them to rub on the pads- you may never see it. Using a run-out gauge (that you could make yourself) would be the best way to see it.

Due respect to Doug, but I'd be surprised if this were a suspension issue- but I have been wrong before. I hope it's something like that so that you're not out any money

I'd clean the rotors thoroughly, and scuff the pads with sand paper (100 grit maybe), usually just using scotch-brite won't get them as clean as a bead blaster. You could take them to a machine shop or someone you know that has one and get them really clean with the bead blaster.
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Old 07-12-2008, 07:19 PM   #15
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Quote:
Originally Posted by Warpbender View Post
+1
Not fast just old.
Thanks but no the tire is fine.

I also am old and not fast. But I have the even faster 1st gen Blue FZ1.
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Old 07-12-2008, 07:21 PM   #16
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I could take them to work and blast them with an aluminum oxide blaster. Will that work? Seems coarse, but I dunno.
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Old 07-12-2008, 07:26 PM   #17
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Quote:
Originally Posted by bumblebee View Post
I could take them to work and blast them with an aluminum oxide blaster. Will that work? Seems coarse, but I dunno.
Blasting them with any aggresive media WILL warp them.
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Old 07-12-2008, 07:28 PM   #18
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Quote:
Originally Posted by tomLSTD View Post

Due respect to Doug, but I'd be surprised if this were a suspension issue- but I have been wrong before.
Brace yourself for a surprise!
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Old 07-12-2008, 07:53 PM   #19
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OK no oxide blasting then.
I will try the runout check just to be sure, but I still feel like if the rotors are warped I would feel something in the lever and it would happen at lower speeds as well.

Thanks again.
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Last edited by bumblebee; 07-12-2008 at 07:55 PM.
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Old 07-12-2008, 07:53 PM   #20
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Quote:
Originally Posted by witchdoctor575 View Post
brake fluid getting hot and making the pads a little grabby?
+1

make sure you are using high temp brake fluid if you're doing more and more track days...
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