My 64 T-bird would easily pop out of park and did so a couple of times. It was due to worn parts in the steering column. Good, new parts would keep the thing in Park but the overall design of the detents was still crap and even after "fixing" it I never trusted it. Many other Ford products used the same design. It required that the lever be "actively" held in park, the stuff in the transmission seemed to naturally want to force itself out of park and the stuff in teh steering col prevented it from doing so. A much better design would be where the "active" effect is to keep it in park and require you to pull it out.