Pro-Cut VBG640, Technical Manual, Page: 11 / 46

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Brake pedal pulsation is most often the result of thickness variation in the brake
rotor. Thickness variation is the technical term for a rotor that is not uniformly
thick. New rotors are uniformly thick, and stop the vehicle smoothly. But thick-
ness variation can develop over time and eventually lead to brake pedal pulsa-
tion.
How does thickness variation develop? Through lateral run-out in the face of the
rotor. Lateral run-out is the technical term for “wobble”, and is a measurement of
how much the surface of the disc wobbles from side to side as it rotates .
A rotor with lateral run-out will not wear evenly, and uneven wear increases over
time. As the vehicle moves down the road with the brakes relaxed, the rotor will
brush each pad once per revolution, resulting in a thin spot on the rotor.
Since vehicle hubs often have lateral run-out due to stacked component toleranc-
es, a new or newly machined rotor will often exhibit excessive lateral run-out as it
turns on the hub. Most manufacturers require rotor run-out to be below 0.002”
(0.05mm). The VBG640 Rotor Matching System allows you to match every rotor
to the hub on which it turns. The on-board computer delivers a precise alignment
between the lathe axis and the hub axis, thereby guaranteeing that a Pro-Cut
machined rotor will have less than 0.001” (0.025mm) lateral run-out every time.
By match-machining the
rotor to the hub assembly
on which it resides, lateral
run-out will be reduced to
below OEM specs every
time!
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