Are they 'floating' calipers, with 4 pistons, 2 on each side then? ie., Can you move the entire caliper easily from side to side on pins/slides? If they are, and you can't, then that would be a possible too. If not, it could be that the hydraulics are at fault, where the outside pistons are applying more pressure than the inside ones..... I'll exit the thread at this point so someone with actual knowledge of your set-up can comment. Good luck

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1986 560SL
2002 Toyota Camry
1993 Lexus