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Discussion Starter #1
I just read all the posts regarding braking vibrations and I think I have a different problem than the steering head bearing issue.

Applying the front brake on my 04 ST4s under 50 MPH results in butter smooth deceleration and stops.

Over 50 MPH moderate to heavy vibration occurs and increases with the amount of braking power being applied. The pulses are felt through the bars but not the brake lever, the fairing shakes noticeably near the top of the windshield juncture and the frequency is approximately 8 to 10 cycles per second.

Everything looks good with the master cylinder, calipers and rotors. this problem just began at about 7,300 Miles. 6,000 mile service was performed at an authorized dealer on time with no issues following the service appointment.

Any ideas would be greatly appreciated.
 

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Front tire cupped, out of balence?
 

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The vibration that you feel above 50 goes away when you slow down below 40 mph or does the vibration remain until you stop?

Take a look at everthing in your front end: wheel bearings, axle, caliper bolts, rotor bolts, fork legs, triple tree and handle bar bolts. If you're not feeling much vibration in the lever, then I wouldn't spend much time checking the rotor run out.

Have you installed new brake pads recently?

How old is the front tire and how many miles on it?
 

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Discussion Starter #6
Thanks to all for the ideas.

The front tire is new and balanced.

I think the rotor bobbin contamination may be the problem and will check that out.

I'll check the front end hardware and steering head bearings as well.

The odd thing is that the vibration goes away as speed drops below about 50 MPH.

That makes me think that the bobbins are a bit stiff, but not completely.
 

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How new is the front tire and was there any vibration before it. Perhaps the front tire has a defect or is the direction correct.
 

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To clean the bobbins, stick the handle end of a rat tail file into them, and turn while you spray brake cleaner onto them - this will free all the crap that accumulates in them.
You dont have EBC pads in your calipers do you by any chance ? Are EBC available where you live ?

Mark.
 

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Discussion Starter #9
Again, thanks for the ideas.

The front tire is a Michelin Pilot Power with 1,600 miles. No problem there and the vibration just began in the last 400 miles.

The brake pads are stock and within wear limits.

I went on a test ride yesterday and did some test stops with cold rotors and the vibration occurred just as it does when they are hot.

I braked hard from 70 down to 30 and the vibration smooths out and goes away at about 50 mph. Odd...

I'll try the bobbin cleaning technique that MarkST described and report back.

EBC pads are available. Are they recommended?
 
J

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John also check to see if your missing any front wheel weights,i had a simular problem and it was found a weight fell off,off balance rim,go figure:confused:
 

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The fact that it only happens above 50 while on the brakes rules out a lot of potential causes. Steering head bearings, for instance, that should cause the problem at any speed. Wheel out of balance, then you would feel a vibration when you're not on the brakes.

So it's something where vehicle speed is a factor...that must mean it's related to the front wheel, since nothing else on the front changes with vehicle speed.

So what would cause a vibration when the wheel is turning fast and the brakes are applied? A problem with the wheel bearings could cause the rotors to get out of line with the calipers when they are loaded by braking, and that could cause them to pulse. Loose caliper bolts could cause the same thing. Or warped rotors, but you said you already checked that.

I vote for bad wheel bearing.:rolleyes:
 

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John also check to see if your missing any front wheel weights,i had a simular problem and it was found a weight fell off,off balance rim,go figure:confused:

I would check the bearing or the weights.
I had the exact same problem after having a new tyre fitted.
I even thought I might have an engine problem it was so fierce so ran the bike upto the same revs in a lower gear hence a lower speed without the shakes appearing. Then tried a higher gear / same speed and sure enough shakes appeared.
Balance was "apparently" fine but turned out the bearing was dry and caused the machine to mis-balance the wheel.....in fact it wouldnt balance the wheel the second time round and eventually took a look at the bearing which was very dry and running slow but no play so hadnt noticed it on the bike.

Replaced the bearing and re-balanced and everything was fine.
Good Luck
 
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