Question: How can I tell if a rotor or drum really needs to be replaced?
Answer: A rotor must be replaced if it is at or below
the minimum thickness specification or discard thickness stamped
on the rotor (this same information can also be found in brake
service manuals). Replacement is also necessary if a rotor cannot
be resurfaced without exceeding the minimum thickness specification
or the discard thickness specification. Replacement is also required
if the rotor is cracked or damaged. Replacement may be recommended
if a rotor has hard spots, is warped, or has been previously resurfaced
for a warped condition.
A drum must be replaced if it is at or beyond the maximum inside
diameter specification or discard diameter stamped on the drum.
Replacement is also necessary if a drum cannot be resurfaced without
exceeding the maximum diameter specification or discard diameter
specification. Replacement is also required if a drum is cracked,
damaged, bell mouthed or too far out of round for resurfacing.
