Dumbest thing you\'ve ever done as a \"Master Mechanic\"?? whats the dumbest thing you've ever done as a "master mechanic". Post them because I'm sure we've all done them! Did you forget to put in oil or water or trani fluid? Confess up...you know what you did.... My dumbest mechanical mistake was going through at least 4(ok maybe 6) ujoints when I first bought my lifted blazer before realizing that I needed to put grease in them. I was changing those damn things in a shirt and tie on the way to work in the mornings in some parking lot! I thought that the stuff that was in them was enough. On a smaller scale...did you ever hear a big clank while your on the road and just then remember that you left a wrench under the hood?