Well if you have rear anti-loc brakes it normal, many people think that rear anti-loc means the rears should not lock up. That is incorrect, it means that then the brakes are applied to the point of lock-up, one one rear wheel will lock, and not both. That is why the ABS option, was an option. The valve need it for rear wheel anti-loc brakes is cheap, and doesn't require an additional electronics. But ABS brakes do, they are more complex and more expensive.