Need help with a K4 750

[Joe Rosenthal]

Hey guys,

I’m posting this in several places hoping for some clues or advice.

Last year I bought a former Vesrah 2004 GSXR 750 race bike. The first time I took it to the local track (ECR), going into turn one, it started shaking pretty bad on the brakes. There’s no pulsing in the lever…. more like the rear wants to skip around. A LOT! It also shakes trail braking until I let off the lever. Needless to say it was pretty unnerving. I talked to some of the more experienced guys at the track and they thought it could be the steering head bearings. We lifted it up and repacked them with grease, but it kept doing it.
The next track day I had a suspension specialist do a basic set-up. It seemed a bit better but the shaking is still there. He made a few small adjustments before the last session but by then I was pretty worn out and decided to call it a day. It’s no fun to ride like that!
The third day at the same track I went out hoping that the suspension adjustments might have cured it, but to no avail.
FYI, it only does this at speed- maybe slowing hard down from 70+. Before the third track day, I ran it up and down my street and it seemed as if the problem had gone. It’s not.

Here’s what I’ve done to the bike since:
Checked front wheel bearings. They’re good
Cleaned and re-packed the steering head bearings and races. Bearings are good.
Had the front wheel checked to see if it’s in balance. It is.
Cleaned the calipers. One piston was sticking a bit, but that’s fixed.
Had the rotor ( Galfer wave rotors) runout checked. They’re fine.
Front tire is not cupped. Bridgestone R10
New rear R10

We test rode it through a parking lot and it shook again, but it didn’t start doing it until a few runs. I watched my friend get on the brakes hard and you can see it waggle around pretty good.

The bike has certainly been crashed (it’s an 11 year old racebike!), but to my eye it looks like nothing too bad. The subframe looks original and isn’t bent or even scratched. The frame looks pretty good too… just normal scratches and no broken or cracked welds. That tells me no tumbling.
Suspension is Traxxion Dynamics front and Penske rear. .95 springs in the front. I weigh 185 without gear.
Any ideas??? I’m taking it to Texas World on the 9th and really want this sorted before I go out there!
I’ll be working on it tomorrow trying to see if there’s anything obvious that I’ve missed.
Thanks,
Joe

[Yorke Oldfather]

I had an issue like that on my 01 Gixxer, I changed the pads out (they were worn out) and the problem went away. Have you flushed the brake fluid and put in new, Motul?

[Joe Rosenthal]

I haven't flushed the brakes yet but the fluid looks perfectly clear and there was no fading... just shaking! I'll do that tomorrow.
Damn this is frustrating... I can't test it on the street. I live in a small town with bored, ****ty cops.
Think it's suspension related? The fella I bought it from told me that the forks had just been redone by Roger at On Road/Off road. Roger is the guy adjusted it for me at a Ridesmart day.
There are a few small chips in the pads on the leading edges. Would that cause the shaking?

[Yorke Oldfather]

Are the rotors glazed? It could be just one rotor, so you might have one grabbing more than the other. I would inspect them closely, inside and out. Other than that, I would consider a new set of pads and bedding them in the correctly. In my case, I installed new pads and bedded them in, and the problem went away through out the day.

[Steve Bui]

I would swap out the rotors just to make sure. Sometimes the rotor is still in spec, but the rotor buttons or minor imperfections cause issues. I had a brembo rotor do similar problems. Since the gsxr is so popular just borrow a set of rotors and try it out. It's a simple thing to do to be 100% sure it's not the culprit.

[Joe Rosenthal]

Well... we swapped the wheel with a spare and put some ratty old OEM rotors that came with the bike on it and took it on a few semi-high speed runs through the middle school parking lot. The problem seemed to be gone...but here's the kicker: the spare wheel has a slight ding in it and the spare rotors are visibly warped! Weird...
I'm going to mount a new tire on the good wheel and see if that was the problem even though the tire looked sound if not just worn.. I've already sanded the Galfer rotors and cleaned the buttons on the carrier.
I won't be able to test ride it again until TWS (Stupid job gives me no time!), so wish me luck!
I was also given some really good advice this past weekend up at ECR by a couple of extremely knowledgeable fellas that told me about the proper "procedure" of mounting the wheel on a GSXR to insure proper alignment!

[Joe Rosenthal]

If the new tire doesn't cure it for that wheel, I'll just swap tires and run the spare wheel and rotors.

[Steve Bui]

Well... we swapped the wheel with a spare and put some ratty old OEM rotors that came with the bike on it and took it on a few semi-high speed runs through the middle school parking lot. The problem seemed to be gone...but here's the kicker: the spare wheel has a slight ding in it and the spare rotors are visibly warped! Weird...
I'm going to mount a new tire on the good wheel and see if that was the problem even though the tire looked sound if not just worn.. I've already sanded the Galfer rotors and cleaned the buttons on the carrier.
I won't be able to test ride it again until TWS (Stupid job gives me no time!), so wish me luck!
I was also given some really good advice this past weekend up at ECR by a couple of extremely knowledgeable fellas that told me about the proper "procedure" of mounting the wheel on a GSXR to insure proper alignment!

Even after I cleaned and sanded the rotors/buttons on my brembo rotor it would still cause the same shaking symptoms. It would get better for a few rides then come back shortly after. I'm willing to bet its your rotors.