Brakes Pulling

Hi... Need some advice....My 66 Barracuda front brakes have just started pulling when applied fast & hard... thought they were just out of adjustment so adjusted them up...that helped some initially. The brakes now pull to the left or the right when applied hard...(never know which way they will pull) not so noticeable when brakes applied lightly. Never know which way they're going to pull. Brake shoes are in good condition....(not that many miles on the brake system) & still running original master cylinder. Thanks for any info!!