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floating brake disc play (on bobbins)

pswiatki

Tuned and Synch'ed
Joined
Aug 26, 2011
Messages
96
Location
Wrocław, POLSKA
Quick question: my bike mechanic said the new discs to be installed on my bike (which I dropped at his service shop together with the cycle) are not as they should be. Specifically: he said there should not be any detectable leeway felt between the centre mount part and the [so called] brake track / outer ring, but there was. So, some play on the floaters (bobbins?) was detected both, axially and radially.

I read some posts here on the forum and could not confirm the above. Quite the opposite: there could be some play between the parts and - once installed - there could even be some rattling when in motion. The unfortunate thing is I cannot go there and verify the situation because I am far away from the shop and we also have social distancing and travel restrictions in place here in Poland. Anyhow, he is reluctant to install those discs and work on my bike is halted now. I described this to the manufacturer and still awaiting their response.
Therefore, I seek your advice. It will be very much appreciated!
 
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I tend to agree with your mechanic. There should be some lateral play, but just about none in the direction of rotation of the brake rotor. Excessive play in the direction of rotation may cause a brake rotor failure which can be catastrophic.
 
Thanks! Good to know. The [German] manufacturer responded and I am not sure what to make of it. They said they never had any problems with their discs, but if the mechanic said he was unsure they (manufacturer) wanted the discs to shipped back to them for inspection. Yet, they did not give me a clear answer if there could be any play on the floaters or no play whatsoever. I only got the info their discs are semi-floating (guess no play allowed!)...
Well... shipping back and forth may increase the cost greatly, I wonder who's going to pay for that. Dammit! We'll see what happens next.
 
My Triumph has floating rotors (like most bikes nowadays) and you can definitely move the braking surface radially and laterally (look at me using big works) and you can hear them. Pretty sure my other bikes do too. Just haven't played with the others.
 
OK, I got the video from the mechanic:



Clearly the brake track moves around on the floaters.
The Germans [manufacturer] saw it, too. They want these discs (both exhibit the same behaviour) back in their workshop. Will happen soon. Will see what they say.
 
OK, I got the video from the mechanic: Clearly the brake track moves around on the floaters. The Germans [manufacturer] saw it, too. They want these discs (both exhibit the same behaviour) back in their workshop. Will happen soon. Will see what they say.
Side to side is perfectly normal, as is the button rotation with a full floating rotor. You actually want that to help with axis deflection from side to side difference with the forks. OEM is "semi" float (hardly visible). The issue would be in the direction of rotation; If there were any movement there, it would be very bad.
 
Side to side is perfectly normal, as is the button rotation with a full floating rotor. You actually want that to help with axis deflection from side to side difference with the forks. OEM is "semi" float (hardly visible). The issue would be in the direction of rotation; If there were any movement there, it would be very bad.
Thank you very much for your answer, Todd. Exactly. The manufacturer said they use semi-floating "bearings" (as they call the floaters) - they call their discs semi-floating. If so, nothing really matches.
Thus, it will be best for them to check the discs. Hope it will happen fast because I am currently wasting time - could have been riding already :) Everything else is all good to go.
 
The video doesn't clearly show any bad play. There may be bad play (play in the direction of rotation) but I don't see it in the video. The play shown, side to side and being able to rotate the float buttons that locate the disk to the carrier, are normal and not a problem. That is how floating, or semi-floating, rotors work.
 
Alright, thank you for your input. The MFG however, saw the video and requested the discs back for inspection. Will post the end result here. By the way: yes, there is play in the direction of rotation. It may not be clearly visible, but it is audible. Perhaps video conversion and processing done by YT on the original material caused this issue. On the original one can see play in both directions.
 
So, here's the update. Discs went back to the manufacturer. They checked and said play (in either direction) was within tolerance. One was closer to the limit and they replaced it so that both rotors would be more equal. Then they sent the rotors back to the workshop. The bike is ready, I shall pick it up on Friday. Since I have ~320 km to cover on the way back home, I will be able to have some impression of how the discs behave. The manufacturer promises no judder. Well.. will see about that.
By the way: I am a bit puzzled because they do have all the approvals from the regulatory bodies (who are pretty restrictive in Germany as far as I know) and they also are ISO quality certified. They say they know the stuff and shared info they make parts for racing as well. So they know their craft. Very interesting.
 
I just checked my Stelvio, 1200 Sport, Centauro, and California Vintage. All have bobbin mounted semi-floating rotors. All move axially about .5 - 1.0mm forwards or backwards with respect to wheel rotation. None have significant vertical movement up off of the bobbins. In that regard, they are all less than .5mm movement.

I have seen many full floating rotors on racing Ducati’s that moved significantly like yours in the video. It’s not unusual as they were designed with that movement.

Given that the manufacturer is giving you the green light, I’d relax and see how they feel. You might be surprised how well they work.

I will be Interested in your feedback!
 
Sure, I will provide feedback Friday afternoon your time, I think. I got scared by this comment from Todd (see above, earlier in the thread):
The issue would be in the direction of rotation; If there were any movement there, it would be very bad.
But something was telling me the parts could not be as bad as my mechanics were telling me. The manufacturer confirmed all was good (I have a feeling they were pretty surprised by my mechanics' claims the parts were not as expected and that they would be reluctant to install those).

When you say the play was 0.5 or 1 mm you mean at the bobbin itself, or - say - the edge of the disc? It makes a huge difference. To answer another comment on the video I posted - it's not easy to capture that play between the disc and bobbins, but once I am back with the bike I shall try to capture a video with a macro lens installed on my camera - it should show everything clearly.

As a matter of fact, I think the play I can detect is a fraction of a millimetre. But it's very subjective and lack tools to measure that with any greater precision. Well.... not that I really need to know that as long as the front brake performs as expected.
 
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BTW - You live in a BEAUTIFUL and ancient city! I will add it to my list of European cities to visit next time I am in Europe.
Thank you much! I like it very much, too. I spent a large part of my life here and just recently came back to the city I got to know so well when I was at the university and earlier when I was a little kid. I am very happy, although for the past 17 years I lived in Kraków, which is also very old and is the historical capital city of POLSKA.
 
Found this too...

“True full-floaters move on the carriers, this allows them to self-center in the caliper for reduced brake drag and "float" unimpeded for unrestricted expansion and contraction during repeated thermal cycling. The only serious down side is a bit of rattle that reminds you these are indeed full-floaters.”

These are the Ducati racing rotors I was speaking about. They are supposed to do this!

 
Oh... thank you much for sharing this video. My rotors are not anywhere near that much of play on the bobbins. Much smaller play on mine. Well.. two more days and I will test the brakes to see how everything works (new rotors, new pads, new pump).
 
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OK, came back home with brakes working really well. Discs do not have as much play [detectable by hand at least] as I thought they would. No judder or any other "special" effects. Brake lever needs some adjustment, but that's just personal preference, nothing more.
Of course, since nothing can be perfect, something had to happen during the ride and it did (big time).
But it is a subject for another thread. No worries though. I am OK and did not crash or anything of that nature.
 
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