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Discussion Starter #1
Let me put you in context first. When I bought the bike it had a bent brake disc, so I had to change it (installed an oem). Vibrations got better but still there.

After that, in a trackday, I noticed my front wheel didn't spin freely on the stand, like it was stuck. We removed one caliper and it inmediately started spinning. On the workshop they told me that a piston was stuck, so we rebuild both calipers, and now it doesn't happen.

The big problem is that it still vibrates. For example if I brake hard the fairing starts vibrating like hell. Moreover, If I approach to a light, and apply light pressure on the lever, the braking is not homogeneous.

They say that they have checked the discs and they are in good shape, but I cannot understand... I tried other bikes and they don't do that...

What do you think? My theory is that there is still one bent disc...
 

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Let me put you in context first. When I bought the bike it had a bent brake disc, so I had to change it (installed an oem). Vibrations got better but still there.

After that, in a trackday, I noticed my front wheel didn't spin freely on the stand, like it was stuck. We removed one caliper and it inmediately started spinning. On the workshop they told me that a piston was stuck, so we rebuild both calipers, and now it doesn't happen.

The big problem is that it still vibrates. For example if I brake hard the fairing starts vibrating like hell. Moreover, If I approach to a light, and apply light pressure on the lever, the braking is not homogeneous.

They say that they have checked the discs and they are in good shape, but I cannot understand... I tried other bikes and they don't do that...

What do you think? My theory is that there is still one bent disc...
What do the brake pads look like ,are they glazed?
 

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Are you sure it's wheel related? If the wheel rim itself is not bent (dinged) and the wheel is perfectly balanced, I would be looking at the head stem bearing races being loose. These can be checked with a 'C' spanner. If they are loose, there will definitely be chatter under braking - more so under heavy braking.
 

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Discussion Starter #4
What do the brake pads look like ,are they glazed?
I don't think so, because we put them new (dp race pads) when did the caliper rebuild.

Are you sure it's wheel related? If the wheel rim itself is not bent (dinged) and the wheel is perfectly balanced, I would be looking at the head stem bearing races being loose. These can be checked with a 'C' spanner. If they are loose, there will definitely be chatter under braking - more so under heavy braking.
Maybe it can be that, I will tell to my mechanic. Btw, last week I hit a rock and bent the rim a bit, but didn't notice anything strange... I have bad luck
 

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I would bet 100% the rotors are warped, or just the one you didn't replace. id bet money on it.
I'm going with warped rotors as well.
Fair enough analysis. Perhaps I was thinking too deep after @anon advised that the discs are in 'good shape'.

Easiest way to check this then is for anon to raise the front on a paddock stand, spin the wheel and apply brake lightly until just touching disc. Surely then he will be able to differentiate whether the brakes are grabbing in a certain spot or not. That, perhaps, should have been the first test.;)
 

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That may or may not work due to there being acceptable and unacceptable tolerance. A really bad warp is usually easy to spot by using the brakes as you indicated but a less noticeable warp may not be identified that way. You'd need a dial test indicator to spot if you are just over the acceptable warped tollerence.

Also you indicated that it's not the pads because you just put new pads. If the rotors were not cleaned, the previous pad's material may have been on the rotors and if you did not clean the rotors and put a different brand/material, you may have contaminated the new ones that's resulting in a grab and let go situation that's causing you problem.

The condition of your tires may play a part as well. Worn, flat spots and such may cause front end feels that we use our imagination to describe

Bad head bearing, loose spanner locks, are also items to look into for undesirable front end input.

But solely going by your description I'd guess warped rotors
 

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Nah, he can't just do a pad and rotor replacement. Sometime you spend a fortune throwing money into a problem without knowing what it is. Trouble shoot and eliminate what is not the problem
 

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Fair enough analysis. Perhaps I was thinking too deep after @anon advised that the discs are in 'good shape'.

Easiest way to check this then is for anon to raise the front on a paddock stand, spin the wheel and apply brake lightly until just touching disc. Surely then he will be able to differentiate whether the brakes are grabbing in a certain spot or not. That, perhaps, should have been the first test.;)
I agree with you here. This should offer a solution to the vibration.
 

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Im only suggesting a pad and rotor change if the case is that they are warped and confirmed that they are. again, I would put money on it being the case. seems like it only has any vibrations on braking and not while rolling, that's pretty consistent with warped or bent rotors. to add, if the calipers are rebuilt, then again its the rotors. Im not about putting money at stuff, but sometimes you don't know until you change the parts out. only a bad thing because of the cost.
 

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Let me put you in context first. When I bought the bike it had a bent brake disc, so I had to change it (installed an oem). Vibrations got better but still there.

After that, in a trackday, I noticed my front wheel didn't spin freely on the stand, like it was stuck. We removed one caliper and it inmediately started spinning. On the workshop they told me that a piston was stuck, so we rebuild both calipers, and now it doesn't happen.

The big problem is that it still vibrates. For example if I brake hard the fairing starts vibrating like hell. Moreover, If I approach to a light, and apply light pressure on the lever, the braking is not homogeneous.

They say that they have checked the discs and they are in good shape, but I cannot understand... I tried other bikes and they don't do that...

What do you think? My theory is that there is still one bent disc...
Have you checked the fork oil in both forks? Are the levels the same?
 

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Discussion Starter #16
Have you checked the fork oil in both forks? Are the levels the same?
Yeah, they worked on them 4 months ago.

But I am in serious trouble now. Last summer in a trackday I realised the front wheel didn't spin freely, something was like breaking it. I removed one caliper and woala!!! It started spinning, so my dealer rebuilt both calipers, just in case (new gaskets and everything), and they also installed an accosatto rcs 18/20 x 19 master cylinder, because the oem one was terrible at trackdays.

Now the other day I put it on the stand, and the exactly same thing is happening (except that both calipers are applying pressure, not just only one). I don't know for how long I've been riding it with this problem. I took it to 3 mechanics and 1 told me it is normal (wtf, the discs are burning even without using the front brake), and the others told me that they didn't know why the hell it was happening.

The front wheel is installed correctly and the pads are rebuilt some months ago, I don't even know what to do... It is terrible having spent so much money and not being able to brake properly
 

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Yeah, they worked on them 4 months ago.

But I am in serious trouble now. Last summer in a trackday I realised the front wheel didn't spin freely, something was like breaking it. I removed one caliper and woala!!! It started spinning, so my dealer rebuilt both calipers, just in case (new gaskets and everything), and they also installed an accosatto rcs 18/20 x 19 master cylinder, because the oem one was terrible at trackdays.

Now the other day I put it on the stand, and the exactly same thing is happening (except that both calipers are applying pressure, not just only one). I don't know for how long I've been riding it with this problem. I took it to 3 mechanics and 1 told me it is normal (wtf, the discs are burning even without using the front brake), and the others told me that they didn't know why the hell it was happening.

The front wheel is installed correctly and the pads are rebuilt some months ago, I don't even know what to do... It is terrible having spent so much money and not being able to brake properly
By chance, are you using stock brake lever? do you know if your master cylinder is stock or aftermarket?
 

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Isn't this fixed yet?

If one disc is 'burning' there might be an issue with the axle spacers being an incorrect size, especially if the bike has been rebuilt or has had major front end repairs. ;)
 
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