Many years ago we had a discussion on the "Charlie Chan Message Board" regarding the character Birmingham Brown, and possible movie quotes related to his feet during times of panic when he was trying to flee the scene. I don't remember the details of our discussion, but I believe we concluded that Birmingham did make several humorous remarks in this regard, but some of the other remarks attributed to him could not be found in any of the films. Perhaps someone else remembers this old discussion, and can supply more details.
You are correct, and I recall the discussion you mentioned which took place many years ago. The exact phrase, "Feet (or "feets") don't fail me now!" was never uttered by Birmingham Brown (or his cousin, Chattanooga Brown, for that matter, in a Charlie Chan movie. There are a couple of instances where Birmingham speaks to his feet, saying something to the effect, "Not now...I'll tell you when..."
Interestingly, a search on Google seems to indicate that Willie Best, who appeared in three Charlie Chan movies, two as Chattanooga Brown, and once as "Himself," is credited for having first used the phrase in the 1940 Bob Hope comedy, "Ghost Busters." Perhaps this may explain why some seem to recall hearing it in a Chan movie. In fact, as the Chan films which featured Mantan Moreland as well as Willie Best came several years after the Hope movie, I would guess that the latter had an effect on the former with regard to one dialoging with one's feet.
