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Offline Coconut

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Re: Pulsing Front Brakes
« Reply #24 on: December 18, 2019, 08:09:56 AM »
A word of caution when checking Disc Run Out .....

The usual method for checking is with a dial gauge attached to a fixed part
of the bike, rotating the disc and measuring any lateral ( side to side ) variation.

This a perfectly acceptable method to use on a vehicle, such as a car,
where the discs are rigidly fixed to the Hub :



The Trophy discs however are "Semi-Floating" - allowing them to
move slightly as the Discs expand and contract from the effects of heat.

The "Bobbins" on which the Discs ( Semi ) Float MUST be kept free
to allow the Discs to move on them, otherwise the Disc could be held
out of true, i.e. not perfectly Vertical, by the seized Bobbins, which will
then give the impression, when measured using the above method, that
they are warped when they could actually be perfectly flat, but held out of true !

If a Disc is measured on the Bike with a Dial Test Gauge, and "appears"
to be warped, I would recommend ensuring the Bobbins are clean and free
( Search "Bobbins" for various methods on how to clean them),
then ride the bike and brake firmly a few times to centre the Discs,
and then take the measurements again.

If you find that there is a "High Spot" and it is exactly opposite a "Low Spot"
this would tend to indicate the Disc being out of true, and not necearily warped.

Unfortunately due to the thickness of the Bobbins, it is not a simple task
to remove the disc and lay it on a Flat Plate to verify whether it is warped or not.

The below Image represents a Flat Disc that is not held vertically.
As the Disc is rotated the measurements between the Fixed Point will vary as shown.






« Last Edit: December 18, 2019, 06:43:01 PM by Coconut »
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