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Offline Coconut

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Re: Brake rotor
« Reply #8 on: September 27, 2015, 05:28:43 pm »
The bobbins allow a little side to side "floating" - that's not what I mean,
and I can't see how seized bobbins would cause this particular issue.

It's not easy to explain so have a look at the attached ( not very good ) image,
which I have exaggerated to try and demonstrate the effect.

The red area represents the wheel and the black lines indicate where the centre of the wheel is.

The blue lines represent the centre of the disc, which is off centre compared to the wheel.

The pink rectangle represents the fixed caliper containing the disc pads,
and the pink rings from it represent the area that would be swept by the pads as the wheel rotates.

As you can see the swept area is uneven due to the disc not being centred to the axis of the wheel.

IF ( and it's a big "if" ), John348's disc is not running true to the centre of the wheel,
then this could be the cause of the uneven wear to his disc, and the vibration he has had.

It's just a theory though, checks and measurements are needed to confirm !



« Last Edit: September 02, 2020, 09:25:30 am by Coconut »

Offline john348

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Re: Brake rotor
« Reply #9 on: September 28, 2015, 04:26:45 pm »
Thanks for the replies I have cleaned the bobbins as I know you should so I did after a reminder from seadog.  Should have done it anyway whether there was a problem or not.   I had taken a feeler guage to the gaps between the floaty bit and the fixed bit and within reason they seem the same gaps definitely not a couple of mil out.  I have to say that one bobbin was just about unmoveable and took a lot of tweaking and work to get free and one was very stiff.  ALL the others were fine (both sides).  Still cleaned and oiled them making sure there was no excess oil to 'spin' out onto the rotors.  I have just been for a run and it seems the same although the brake lever seems need a lot less movement and is very firm.  But as I swap between bikes a lot it is difficult really to say.  There is still a bit of noise and 'buzz' from the brakes so I will check again.  As coconut says the next thing is to get a dial guage on the edge and spin the wheel to measure radial run out.

Offline Ernest T

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Re: Brake rotor
« Reply #10 on: September 28, 2015, 06:42:33 pm »
I've had considerable pulsing at the front brake lever on mine and the dealer said there is very little  run out on the disk, just a couple thousands of an inch.  I took 220 grit sand paper to mine this weekend to see if there is any pad residue that could cause the problems.  I used a flat piece of steel bar behind the sand paper and was surprised by how badly the disks are grooved. The groves are shallow and the disks really feel flat, but the fine sandpaper clearly showed there are ridges on the disk.  I haven't ridden it yet so I can't tell you if it made a difference.

Offline Ernest T

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Re: Brake rotor
« Reply #11 on: September 29, 2015, 04:16:22 pm »
Sanding the brake disks did absolutely nothing for the pulsing at the lever.