Hot'n'sticky brake sense check, please

[defblade]

2016 Toyota Corolla, not used as much as it should be, so regular brake issues meaning I'm slowly changing everything, one problem at a time.

Anyhow, I recently changed the rear pads, discs and shoes. Normal single piston sliding calipers, with the shoes in the disc hub.
Passenger side is fine, driver's side got smoking hot last time I drove it.

When I took it apart the first time, the inside pad (so against the actual piston) was hard to get out and much thinner than all the others.
I cleaned up the pad carrier clips and lubed the new pad's ears and it moved ok when I put it back together, and acted perfectly normally today when I investigated.
I backed off the handbrake shoes a fair bit today, as there was the slightest hint of them dragging turning the hub forwards. (Will need to re-adjust eventually to get the handbrake working better again, but this is removing possible causes.)
I couldn't push the piston back in with my hands (it doesn't need to be turned/wound back, just pushed), which I often can, and it took a fair bit of leverage to get the caliper off the pads. But the piston went back with my winding-back tool, as it did when I changed them in the first place. I pumped it out/pushed it back a few times off the carrier and it did move each time.
The sliders are lovely and free to move with light finger pressure.

Put it back together and a few miles later, it's hot AF again.

So between the piston not moving on grip pressure, and the original pad having worn massively on the piston side, I'm thinking the piston is sticking enough in use to cause problems, and it's new caliper time?

[GreenV8S]

If the caliper is sliding correctly then you'll always get equal wear on both sides.

Accelerated wear on the piston side suggests either the slider is the problem, or there's some external force applied to the caliper. (Being free to move when unloaded is no guaranty that it's OK.)

[defblade]

GreenV8S said:

If the caliper is sliding correctly then you'll always get equal wear on both sides.

Accelerated wear on the piston side suggests either the slider is the problem, or there's some external force applied to the caliper. (Being free to move when unloaded is no guaranty that it's OK.)

This is why I posted... it sorta seemed obvious, but at the same time, there's a nag in my head from knowing the wear should probably be fairly equally distributed, even if the piston is the only sticky bit.

What could be adding an external force???

I will order the slider replacement kit at the same time, seems pointless not to renew it while it's apart if there's any chance it might be the sticking point problem.

[GreenV8S]

The original uneven wear points to a problem with the slider.Have you removed and inspected them, or just confirmed they move freely? Not all slider problems will show up when they are unloaded.