Chester Vandermark (plaintiff) purchased a new Ford automobile from Maywood Bell Ford (Maywood Bell) (defendant), an authorized Ford dealer. After Vandermark had driven the vehicle about 1,500 miles, he lost control of the car after he applied the brakes, veered off the highway, and collided with a light post and suffered serious injuries to himself and his sister, Mary Tresham (plaintiff). Vandermark and Tresham brought suit against Maywood Bell and Ford Motor Company (Ford) (defendant), the manufacturer of the vehicle for breach of warranty and negligence. At trial, Vandermark provided an expert on the operation of hydraulic automobile breaks who testified that, in his opinion, the brakes applied themselves after failure of the piston in the master cylinder leading to Vandermark’s loss of control of the vehicle. The trial court struck the testimony and rejected Vandermark’s offer to prove that all of the possible causes of the piston failure were attributable to all defendants. Thereafter, the trial court granted Ford’s motion of nonsuit as to all causes of action against it and directed a verdict in favor of Maywood Bell on the warranty causes. The jury returned a verdict for Maywood Bell on the negligence claim and the trial court entered judgment on the verdict. Vandermark and Tresham appealed.