Rust jacking is a specific brake pad failure common in salt-belt climates, and it can ruin pads long before the friction material wears out. It is worth understanding because it is preventable with the right pads. Here is what rust jacking is.
What rust jacking is
Rust jacking happens when the steel backing plate corrodes UNDER the friction material. As rust forms and expands between the plate and the pad material, it physically lifts (jacks) the material off the plate, cracking and eventually delaminating it - see brake pad delamination. The pad can look fine on the surface while failing from underneath.
Why it happens
It is driven by moisture and road salt reaching the bond between the plate and material, and by backing plates that are not properly protected against corrosion. Cars in snowy, salted regions are most affected, and cheap pads with bare or poorly-coated plates are far more prone to it than quality pads with corrosion-protected plates.
The warning signs
Look for friction material cracking or lifting at the edges, chunks separating, or a pad that is failing despite having thickness left - often with noise. Because it starts hidden under the material, it can surface as sudden cracking or a chunk breaking off; see brake pad edge cracks.
Prevention
The fix is quality pads with galvanized or coated backing plates that resist under-material corrosion, and replacing pads before they get old and rusty. In salt country this is worth paying for. Fit quality corrosion-resistant pads with fresh hardware to avoid rust jacking.