The Ford truck was not modified to do the stunts, it was pretty much box stock. The Ford Motor company used clips from the movie in television commercials to demonstrate how tough their trucks are built.
On the first day of production, Charles Bronson got angry about a delay caused by a late transport truck carrying cars necessary for the scene that was to be shot. Finally, he yelled to director Richard Fleischer within earshot of the entire crew, "You know what this company needs - it needs a European first assistant and a European crew!" The crew was so insulted by this remark that at the end of the day, they told Fleischer they would be leaving the production. They were persuaded to stay, but for the rest of the shoot they never spoke to Bronson unless they absolutely had to. Later in the shoot, Bronson commented to Fleischer, "I just don't understand it. Nobody calls me 'Charlie' on this picture. They only call me 'Mr. Bronson'."
The farmer-owner of a 160 acre watermelon ranch and farm near Manzanola in the American state of Colorado, where exterior scenes were filmed, was initially allegedly offered about US $1000 - US $3500 for the use of his land for the film. However, upon learning that this movie had Hollywood movie stars in it, and the fact that the picture had been announced as a multi-million dollar venture in the "La Junta Tribune-Democrat" publication, the Melon owner-farmer reportedly increased the price from US $3500 to US $10,000.
After its initial theatrical run, the movie played as a supporting feature at New York cinemas showing the 1974 James Bond film L'Homme au pistolet d'or (1974), after the latter film had proved a weak performer at the box-office.
Screenwriter Elmore Leonard wrote this with Clint Eastwood in mind. Leonard had previously written the screenplay for Eastwood's Joe Kidd (1972).