Date: 20-09-18  Time: 12:20 PM

Author Topic: Front brake discs: Bobbins  (Read 136 times)

agricola

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Front brake discs: Bobbins
« on: 16 September 2018, 08:52:52 PM »
Trackday week after next, so had the bike on the ramp for a thorough check over. Never noticed before, but the bobbins on the front brake discs have a white mark on each one, on the inside faces only, as per the photo. Anyone know the purpose of said marks? Do they need to align with the slit in the disc? Opinions welcome ta

Grahamm

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Re: Front brake discs: Bobbins
« Reply #1 on: 18 September 2018, 10:47:38 PM »
Quote
Anyone know the purpose of said marks? Do they need to align with the slit in the disc?


No, the bobbins are there because of the "floating brake discs" which allow the actual disc to move in relation to the inner to stop it warping if it gets hot due to serious use.

The bobbins should actually be able to revolve, it's a good idea to check them occasionally. Get a nut and bolt that will fit through the hole, tighten it enough that it grips the bobbin, then try to get the bobbin to revolve. If it doesn't, spray it with some brake cleaner (DON'T use anything lubricating, unless you want to risk your brakes not stopping you at all!) and it should eventually shift.

Here's a video that may help. The useful bit starts at 2'30"



If you're going on a track day and going to be doing heavy braking, this is well worth doing, rather than risking warping a disc!

Fazerider

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Re: Front brake discs: Bobbins
« Reply #2 on: 19 September 2018, 01:10:23 PM »

I can’t think of any reason to mark the position of the bobbins unless a previous owner was interested to see if they rotate in normal use.


I didn’t clean my bobbins for the first few pairs of discs I’ve used, but the last lot of OEMs I did and the mileage from them didn’t improve. Now on EBCs with their SD system (which can’t be rotated) and these do seem to be lasting better.

YamFazFan

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Re: Front brake discs: Bobbins
« Reply #3 on: 19 September 2018, 05:10:40 PM »
My 2003 foxeye, which is still on the original discs, has similar markings. I wonder if they are applied at factory assembly?.





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