The parking/hand brake on the 4Runner didn’t work; I figured out why when doing the brake-overhaul, and finally had the chance to address it today.
The parts sit inside a rubber dust boot, which in this climate means 6-month-saltwater-pool. This rusted the bellcrank enough to rust-jack the cast aluminum bracket into several pieces (which were gravel-like inside the rubber boot). This is by far the rustiest thing I’ve seen on this car.
Not only does this brokenness mean the mechanism is free to do whatever it wants rather than apply the brake (held in place by the springs and mechanism inside the drum), it also impacts the self-adjuster in the drum, which sort of levers off the end of the bellcrank.
New parts were installed; the parking brake works now but isn’t particularly strong and only comes on at the top of the travel. The part pictured was adjusted as described in the service manual (thanks, google) so it’s probably a matter of the handle-end needing adjusted. Most importantly, the self-adjuster on the rear brake should now work properly.