Abstract: In an anti jack-knifing coupling arrangement between a tractor vehicle and a trailer wherein a turntable is mounted on the tractor vehicle for rotation about a vertical axis and carries a brake member for rotation therewith and having opposing horizontal parallel faces defining brake surfaces and brake callipers are mounted on the tractor vehicle for operative engagement with such brake surfaces, while themselves being restrained from movement about the vertical axis; the brake surfaces and the brake callipers are cooperatively disposed in a manner so as to be protected from exposure to rain and like elements and are kept clean and dry so that any possible slippage therebetween when the brake callipers are actuated to grip the brake surfaces is obviated.