Only because of driver incompetence, inexperience or inadequate maintenance. Both Constructor drivers I have spoken to, Stan Wass and Bert Paul, praised the gearbox. When you think about the punishing payloads civilian Constructors undertook while operated by Pickfords, and others, and see how many of these vehicles have survived into preservation still with their original gearboxes. I was requested, via my weegie board, to post this rebuttal by Scammell craftsmen who have passed on to the other side and are pretty irate at this unfounded slur. I'll go back on there tonight and try to calm them down a bit.