When I changed out the brake pads at 177k miles (99 Ltd), I found the outer pads had considerably more wear than the inner pads. Outer were 5mm thinck, inner were 2mm thick, both right and left sides. Other than the difference between outer and inner pad wear, all pads had worn evenly. This is the second set of Toyota oem pads for this truck.

I assume this is due to caliper flex during braking. The inner half of the caliper is bolted the hub, so any flex of the caliper is translated to the outer half. That means when pressure is released, the outer pads have to retract further than the inner pads to prevent any residual drag on the disc. Slight flex in the piston seals is supposed to provide clearance for the pads to retract. It appears that isn't sufficient for the outer pads.

I noticed a similar pad wear difference on an 01 Tacoma PreRunner with the same 4 piston calipers. It also has 170k miles and is on the second set of oem pads.

Has anyone noticed this kind of uneven wear on new calipers? I'm wondering if the seals have hardened over time, and are not retracting as far as when new? Would new piston seals alleviate this issue, or is caliper flex too much for new seals to accommodate?