[Shop-talk] Pulsing brakes

[Neil Sherry]

Run out is slightly less critical, as the pads should float back and 
forth to accommodate it (unless the callipers are really sticky). If one 
area of the disk is thicker, then that will cause a definite pulse, as 
the extra material has nowhere to go. Could be caused by a hard spot in 
the disk that has been left high as the rest of the disk has worn away.
Another possibility is if the edges of the disk are horribly corroded to 
the extent that bits are flaking off, this can give an uneven running 
surface for the pad - but that would be quite apparent without dti's and 
mic's.
It is possible that the run out is caused by a warped disk - this can be 
caused by heavy braking to a stop, followed by holding the brakes on 
whilst stationary - the pads keep one bit of the disk hot while the rest 
can cool more quickly. Or it's just one of those things as the disks wear!
Neil


On 22/06/2011 07:30, Randall wrote:
>> I have a dial indicator and a magnetic base, so there are no
>> good tools to
>> acquire on this issue,
> FWIW, my book recommends using a micrometer to measure the thickness
> variation.  I don't recall the spec offhand, but it's much tighter than the
> runout allowance.  Not sure why that is, but it might have something to do
> with the ABS.
>
> -- Randall
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