ABS- Whenever I see an older vehicle featuring RABS, I laugh. What a dead stupid idea. You're in the slick, you need to steer. You pin the brakes, actuating the RABS. Great. The fronts lock up- now you can't steer... duh...

I used to own a truck with RABS; the only reason it came with it was because I ordered the payload package when I ordered the truck. The base trucks didn't have ABS yet; the following model year, 4 wheel ABS was standard across the board.
When I asked the mechanics at the dealership why I had to put up with exactly the behaviour you described, they said it was because they had had so many problems with the old load proportioning valve setup they had run previously.
I've since seen a truck with the old system; I can also see why the factory went with RABS as a stopgap while they were developing the 4 wheel technology (doesn't mean I liked it, just that I can understand it).
The old system consisted of a rotary valve mounted on the frame rail, with a linkage attached to the rear axle; the more you loaded the truck, the lower it sat compared to the axle, thereby opening the valve to let more brake fluid signal get to the rear brakes. Two problems; 1] if you panic stopped with a load, as weight was transferred forward, it unloaded the valve, putting all the braking load on the front (just like RABS in the snow), and 2] the valve cycled with every twitch of the suspension, leading to a lot of wear & tear,eventually causing it to fail with the resultant loss of brakes.
Just though I would help clarify why some older vehicles had such a bizarre braking system in the first place.......
