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I have an electric road bike that has SM-RT64 Shimano centerlock brake rotor in the front. I have noticed that when I press the front brake and try to rock the bike back and forth, there's some free play somewhere in the braking system.

I checked for free play in the headset to find nothing.

I checked hub (HB-R7070) bearings for looseness but they weren't loose.

I checked that the disc brakes have the pad retaining screw tight.

When I rock the bike back and forth, it doesn't seem to be the brake pads that are loose. The looseness seems to be at the centerlock brake rotor. It is not the fixed rivets connecting the spider to the disc that are free; instead, the brake disc seems to be rocking back and forth at the hub, and the lockring seems to be rocking along with it. Thus, the brake disc - hub connection is of suspect.

Related information found online:

What could be the cause?

Is the brake disc defective?

Are the aluminum centerlock splines in the hub damaged? (I hope not as it took about 5 hours to build the front wheel, and swapping the hub to another would take another 5 hours).

Or is the centerlock design just too weak for the massive braking forces I need (my weight is over 100kg)?

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  • Aside - there is a dead youtube link in there, so shows "This video is unavailable" Is there a replacement?
    – Criggie
    Aug 18 at 8:38
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The cause is a missing aluminum shim between the centerlock lockring and the brake rotor.

I removed the brake rotor from the defective front wheel. Then I removed a brake rotor from a known-good front wheel. When closely inspecting the lockrings, I noticed something the known-good front wheel has that the defective front wheel didn't: there was a very thin aluminum shim between the centerlock lockring and the brake rotor.

When I built the front wheel, having had no prior experience with disc brakes, so I thought the aluminum shim is something that should be removed and the centerlock lockring should be tightened without it.

Now I have swapped the lockrings and the brake no longer has free play.

The missing shim probably has been thrown out along with garbage, so I have to purchase a shim somewhere.

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  • Value wise, you could purchase a complete spare disc and use the included shim, retaining the spare disc for when the current one expires
    – Swifty
    Nov 29 '20 at 18:04
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    I am not convinced this part is necessarily always aluminium. The cheaper discs use steel lock rings, the more expensive ones aluminium. Maybe the washers are always aluminium? I don't know though. The washer is clearly marked in all of Shimano's exploded diagrams si.shimano.com/api/publish/storage/pdf/en/ev/BR-MT200/… The washer is not a separate part number, but the lock ring is. Steel lock rings (with washer) are cheap, on ebay. If you want an alloy one to save 5g, then they cost a bit more.
    – thelawnet
    Nov 29 '20 at 18:09
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    Good find. Could you add a photo of the shim to the answer? That would enhance.
    – Criggie
    Nov 29 '20 at 21:08
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    I’m surprised the tolerances are so stringent that a 0.1mm shim makes that much of a difference.
    – MaplePanda
    Nov 26 at 23:18
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I found a simple solution and it works fine. Cut and place a piece of cookie wrap plastic packaging around the hub spline (0.05mm thick would be ideal) and insert the disc. it will require some pressure and voila ... the problem is over.

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  • you're doing great - I've just edted that info into your answer. Improving the Question and the Answers is a part of how Stackexchange is designed. You can learn more by browsing through the tour
    – Criggie
    Nov 28 at 18:17
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This is a common centerlock issue for which there is no solution. You have to live with it or change your hubs and rotors

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    Hi, welcome to bicycles. Do you have any support for this? OP has posted an answer that works for them, so it appears that there is a solution. A good answer should include relevant evidence; you might want to read How to Answer and take the tour.
    – DavidW
    Aug 18 at 14:35

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