>From the "MGB Handbook" by Stuart Turner and John Organ
"Scored brake discs are not detrimental, provide that the
scoring is concentric and not excessive, but heavy or uneven
scoring will impair brake efficiency and a new disc (or discs)
must be fitted or the offender re-ground. reground discs,
however, should only be resorted to if new discs are
unobtainable. If re-grinding takes place it is important that
it is carried out accurately, removing a total of not more than
0.040 in. thickness of metal. The amount may be removed by
taking off 0.020 in. from each side of the disc or by removing
0.040 in. thickness from one side only. A total thickness of
more than 0.040 in. must not be removed and after the discs have
been ground the faces must run true to within 0.002 in. and be
parallel to within 0.001 in.
"Whether re-ground or new discs are fitted it is important to
ensure before fitting them that the faces are absolutely free
from burrs. when the discs are in position on the car they
should be checked for 'run-out' during rotation by a dial
indicator. The 'run-out' on the periphery of the braking surface
must not exceed 0.004 in. In the vent of this being exceeded,
the disk should be removed and repositioned until a more
satisfactory measurement is obtained."
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