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I run a BMC four stroke 03 with XT disk brakes (standard components) on a Reba Race fork. Had them for 6 months. All of a sudden however, I've noticed that there is play in what I thought was the headset. When I brought the bike into my local shop (Castro Valley Cyclery) I was told that the problem isn't the headset (whew!) but that the floating rotors are casing that and it's completely normal... really? I'm not a gear geek and I can't tell you the latest change in the thickness of the latest rotor on the newest fork. Some of you out there however are and can... I'm hoping you can shed some light on this. I'm thinking of taking it to another shop but I want to understand the potentials involved here. Is there supposed to be any play in floating rotors when at rest and cool? Could it be something else in the system? Any help would be appreciated.

q
 

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XT brakes

Hi!

Are your disc brakes, the old(2001-2003) Shimano Deore XT disc brakes, where the calipers each has 4 pistons? If your brakes are the old disc brakes, please write to me to my email: [email protected], because I own these brakes myself and I think I can help you with problems regarding these brakes. On the other hand, if your brakes are later XT brakes, I can't help you, and therefore you don't have to write me.

Kind Regards

Jan
 

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I have never heard of any floating discs before. ¨The fact on the thin(2 milimeters) discs is that they can bend or flex a little from side to side, as the front wheel is stressed from the bike ride or when activating the brake(especially if the caliper is not centered directly upon the disc). On the other hand, floating calipers exist. Floating means that the caliper is equipped with a "mechanism" that allows the caliper to slide from side to side. An example of a floating disc brake system, is the Magura Gustav M system. Unfortunately, I am unaware of any floating capabilities of the never XT brake systems. As I can see from Shimanos webside, the never XT system has two opposed pistons. If you are in doubt about your problem, contact another bicycle repair shop and let them give you a second opinion. The first repair shop may have given you the wrong answer/estimate to the problem.

Jan L
 

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i have seen this as well, i am using 160mm on the 765 centerlock. i thought i had a similar problem with the headset, but it was that the CL splines had developed play. i tightened up the lock ring at it was better. but not nonexistant. use a 3/8 torque wrench if possible and the play is much less then 6 bolt. i have never got enough play to grind a disc into a caliper with ths system, but i assume that 1mm of play could have a damaging effect to the rotor center if it were to say jam under full force of braking, ive ridden mine since and haven't had any problems. i think the idea is that the brake is only designed to work in one direction, so at the beginning of a ride do a few slow speed stops before jamming on them full throttle.
 

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There could be a few other reasons why there is play when you rock your bike the way you mentioned above, but the least likely will be in the rotors.

The most likely will be the headset then your hubs. Have another shop have a look at it. I presume you have tighten up your QR correctly.

When you rock the bike have a look at the spacer just above your top headset bearing cup to see if there is play there. That will tell you if it is the headset, then you will have to have a look at your hubs. Get someone else to hold the brakes in and rock your bike and have a closer look at the brakes and hubs region. You should be able to spot the play visually.
 

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GTV8 said:
While you are at it check your fork for play between the upper and lowers, the bushings could be worn.
turn the handlebars 90degrees, and rock fore/aft. if play still exists, it's your headset. if not , then it might be the fork(doubtful but possible), loose axle or br0ken hub.

my mono m4's did have a little play fore/aft when the front brake was totally locked, but this was just the brake pads moving parallel to the direction of the movement. not a big deal. it really shouldn't do this but i guess as long as you're going in one direction you'd be okay.
 
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