Date: 19-11-18  Time: 12:15 PM

Author Topic: Front brake discs: Bobbins  (Read 466 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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agricola

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Re: Front brake discs: Bobbins
« Reply #4 on: 20 September 2018, 06:15:36 PM »
Yea, I clean and rotate them a couple of times a year, but Ive never noticed the marks before. I just cant think of a reason for them

YamFazFan

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Re: Front brake discs: Bobbins
« Reply #5 on: 20 September 2018, 09:15:25 PM »
I've asked my bike mechanic/salesman friend about this.

He says the white marks are applied on the assembly line in order to indicate that the parts have been correctly fitted. The guy further down the line then knows that it's OK to fit subsequent parts. A kind of quality control I guess.
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Re: Front brake discs: Bobbins
« Reply #6 on: 20 September 2018, 11:36:53 PM »
I've asked my bike mechanic/salesman friend about this.

He says the white marks are applied on the assembly line in order to indicate that the parts have been correctly fitted. The guy further down the line then knows that it's OK to fit subsequent parts. A kind of quality control I guess.
I dont have them on my bobbins but I have blue marks on the disk Alen bolts - perhaps a dab of the same threadlock that prevents people from removing them when they need to
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Dynspud

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Re: Front brake discs: Bobbins
« Reply #7 on: 21 September 2018, 06:41:42 PM »
How do you rotate the bobbins that don't have holes through them and won't take a bolt?  :\
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agricola

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Re: Front brake discs: Bobbins
« Reply #8 on: 22 September 2018, 02:51:01 PM »
I've asked my bike mechanic/salesman friend about this.

He says the white marks are applied on the assembly line in order to indicate that the parts have been correctly fitted. The guy further down the line then knows that it's OK to fit subsequent parts. A kind of quality control I guess.


Thatll do. Thanks

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Re: Front brake discs: Bobbins
« Reply #9 on: 22 September 2018, 05:57:38 PM »
Fully floating bobbins rotate freely but Fazer discs are semi floating aren't they? I don't think the bobbin needs to be free enough to spin. Putting a bolt on them and spinning them might be doing more harm than good. A spray of brake cleaner should be enough to keep them clean.  There's no mention of the bolt through the bobbin trick in the Yamaha workshop manual or any other manual I've read. Think I'll stick with Yamaha over youtube

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Re: Front brake discs: Bobbins
« Reply #10 on: 22 September 2018, 10:48:36 PM »
Bobbins on my FZS600 2003 Foxeye are solid with no hole and no sign of movement in them, still on original disks at 37K so I am guessing that is the way they re meant to be.
They are the same as YamFazFan's picture above

« Last Edit: 22 September 2018, 10:49:27 PM by tommyardin »
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YamFazFan

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Re: Front brake discs: Bobbins
« Reply #11 on: 23 September 2018, 11:00:53 AM »
Bobbins on my FZS600 2003 Foxeye are solid with no hole and no sign of movement in them, still on original disks at 37K so I am guessing that is the way they re meant to be.
They are the same as YamFazFan's picture above


There should be a limited amount of movement in use.

The camera work is horrendous, but this short video shows the difference between semi and full floating fairly well.

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Re: Front brake discs: Bobbins
« Reply #12 on: 25 September 2018, 07:47:31 AM »
hi gents you can buy bobbins from black shadow should you need to rebuild a disc  :)


http://blackshadow-uk.co.uk/index.html

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