[Schurkey]

Originally Posted by grivera

Does upgrading front from 11” to 12” disc require different spindles or caliper brackets?

Originally Posted by Scarebird

yes, and only works on 1970-81 Firebirds.

For the record, the " spindle" is the steel "rod" that's pressed-into the iron casting; together they're called the "Steering Knuckle". The iron casting also includes the caliper mount, if we're talking about the OEM GM A/F/X/B/C steering knuckle design--essentially the same geometry although several different casting numbers/part numbers owing to different bearing sizes or casting revisions. The 12" knuckle/rotor system fits heaps and piles of GM vehicles including those retrofitted with the H-O Racing "Tall Spindle" disc brake conversion for '64--'72 A-body.