What you describe with putting weight in the back runs on "the same," proinciple I was trying to describe before. Putting half a ton of sand or bricks in the bed gives the back better traction, and maybe even keeping better traction in hard braking. Under that circumstance, the fronts, having less traction, will skid before the rear -- all else being equal, or braking system designed for "normal" F/R weight distribution.
It's possible to stop with rear brakes only, but stopping distance would be awful compared with front-only, and all due to the force distribution involved in the dynamics of braking.
Yes - you've got it. We basically presented abnormal weight distribution to a braking system designed for normal weight distribution. I lived it. Back in a different era, when us survivors had real-life physics instructions that you don't often get in school. I had a little excitement one time with the loaded-bed truck, backing down a snowy hill, and applying the brakes to keep my speed down. And it was down, but even at 2 or 3 miles per hour, the truck managed to swap ends as the fronts locked and it just swung right around on me. Kind of quickly too! White knuckles for a minute, after which I thought "that was cool".
I guess we're diverging from the Q talk. Is this what is referred to as a thread slide? Unintentional, I promise. Human nature and all.