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Offline john348

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Brake rotor
« on: September 26, 2015, 04:18:48 pm »
OK here is a strange on.  Just had new tyres and new brake pads.  Was in San Francisco straight afterwards so did't ride much.  Anyway got back used the bike and got a vibration from the front when braking.  I have always found this when the bike has been standing for a few days.  For example after the head change it was bad so I actually complained only to be told that there was nothing wrong (they didn't even check it.....  So I will not go back to that dealer).  So after  few miles and some heavy braking it goes away so I assumed it was just something on the discs.

Back to the story this time it was quite a vibration especially as the speed came down (really the idea of braking).  I have gone to check today and the RHS disc (looking forward) which is the linked disc has worn fine for half the disc but then the wear marks get closer to the centre for the other half.  So for the good half the witness marks are perfectly in line with the disc only outline but on the other half the marks start to wear the webs that hold the disc to the floaty bits.  And as these are proud from before I think that is where the vibration is coming from. When the pads wear down obviously this will go away.  I have looked at both sides of the disc and it looks the same in the same place (as you would expect). 

I was wondering if anyone else had this sort of issue?

Offline seadog

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Re: Brake rotor
« Reply #1 on: September 26, 2015, 04:56:12 pm »
John348

Can you possibly send some photos. I take the "floaty bits" are the bobbins? A dealer did this so I presume they fitted the front wheel correctly with the correct spacers in each side.
They have used correct pads.

be interesting to see the outcome of this.

seadog
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Offline john348

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Re: Brake rotor
« Reply #2 on: September 26, 2015, 05:13:02 pm »
Well I fitted the pads so can't blame them.  The strange thing as I say is that it is fine on one half and overlapping on the other half it is only over lapping by around 1 to 2mm I have a picture and am about to upload.

These are 2 pictures of same rotor one from 'good' half and one from 'bad'.

Offline Coconut

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Re: Brake rotor
« Reply #3 on: September 26, 2015, 08:02:56 pm »
Am I correct that the Photo's are of the same Disc / Rotor ?

If so then the only thing I can summise is that the Disc is not running true to the centre line
of the axle about which it rotates - like a mild "Cam".

This is easily checked if it's out by that much - with the wheel off the ground spin it
and watch the outer edge of the disc as it passes trough the fixed caliper -
if it is moving in and out of the caliper slightly then this shows it is not centralised to the axle.
( You could also use a Dial Gauge fixed to the caliper with the probe on the outer edge of the disc
to measure the actual amount of run out ).

There is nothing in the Service Manual for adjusting such run out,
just specifications for minimum thickness of the Disc and maximum allowable side to side run out ( warp ).

It is possible that the Disc has been manufactured out of true, and this might explain why you
( and several other Members ) have reported such Vibration / Pulsing -
which then goes away after some Heavy braking - as the pad will be hitting parts of the disc ( those webs )
that they are not meant to touch and will vibrate or pulse, and then wear away under heavy braking -
at least for a while !   :084:

Another reason might be wear in the Disc mounting holes or bolts,
that have allowed the disc to move slightly out of the centralised position it should be held in
if the holes and mounting bolts are not worn.

The more I think about this, the more likely I think it is that the disc will be "off centre",
and those that have reported "Pulsing" to their Dealer may have been told "It's normal" as they
have probably only checked for side to side run out ( warping ) and found that to be within limits
while the cause was "off centre" run out that has not been checked for -
maybe there was a "bad batch" of discs ???   :084:

All very interesting - can you check this rotational run out and let us know what you find ?

Cheers  :821:

« Last Edit: September 02, 2020, 09:25:53 am by Coconut »

Offline john348

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Re: Brake rotor
« Reply #4 on: September 26, 2015, 09:15:20 pm »
Will do also I will try to find Webb's of Lincoln to see what they say.

Offline seadog

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Re: Brake rotor
« Reply #5 on: September 27, 2015, 11:02:16 am »
John

This may be a silly question but here goes. Are the bobbins loose i.e. can you turn them. They do look abit dirty and could be stuck. If so the disc is not "floating"  when you put the wheel back on it does recommend you bounce the suspension up and down a couple of times. For the amount of wear on the bad side this may not be the case case.

There are a few ways to check and clean the bobbins. The easiest way I do is get some long nose thin grips Grip the bobbin in the hole and outer edge and turn them loose. Using brake cleaner to clean all the crap out.
This is a strange one. If what coconut said it may be worth stripping the clipper down again clean the caliber well and check the wheel alignment for any play. If it was a bearing issue I think you would notice the wheel moving not just the braking.

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Offline nert

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Re: Brake rotor
« Reply #6 on: September 27, 2015, 02:13:42 pm »
Looks like pads are installed improperly or miss manufactured.

Offline john348

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Re: Brake rotor
« Reply #7 on: September 27, 2015, 02:49:56 pm »
I am washing the bike today so will free the bobbins.  Yes my bike is usually dirty as I ride it too much???  As for badly installed or badly manufactured I can accept that! as I put them in! although I am not sure how you can install them badly. I cleaned the pistons, cleaned the calipers, used brake grease on the backing plates and copper slipped the pins when I reinstalled them? But I am not sure how you install them so badly that the wheel or rotor is off centre (I didn't use a hammer once).  Yes the tyres were changed a couple of days before I changed the pads.  I have looked at the pinch bolts and nothing seems to be awry but I will try and loosen them and bounce a bit???

I only asked as others have had 'run out' as mine has been bad right from the start and it did always seem to be that rotor.  I complained to the dealer within 2 days of getting the bike, then complained after the recall and then complained at first service (hence me changing dealers).

Anyway about to go and loosen the bobbins and if I get enough oil and grease around them the brakes will be a lot smoother  :084: Ok I will try to not get 'much' on the rotor.  If I get to the dealer tomorrow I will let you know.