Rambler models (1962 through 1966) used a flange and cushion mount in place of the ball and socket. Since the torque tube does not constrain the car's body to the axle in the lateral (side-to-side) direction a panhard rod is often used for this purpose. The combination of the panhard rod and the torque tube allows the easy implementation of soft coil springs in the rear to give good ride quality, as in Buicks after 1937. Before 1937, Buicks used leaf springs, so the panhard rod was not used, though the torque tube allowed a cantilever spring suspension, which gives a softer ride than a center-mount axle on the leaf spring, as required by the Hotchkiss setup. In addition to transmitting traction forces, the torque tube is hollow and contains the rotating driveshaft. Inside the hollow torque ball is the universal joint of the driveshaft that allows relative motion between the two ends of the driveshaft. In most applications the drive shaft uses a single universal joint which has the disadvantage that it causes speed fluctuations in the driveshaft when the shaft is not straight. The Hotchkiss drive uses two universal joints, which has the effect of canceling the speed fluctuations and gives a constant speed even when the shaft is no longer straight . V8-powered models of the 1963-1966 AMC Rambler used a double-Cardan constant velocity joint to eliminate driveshaft fluctuations, though six-cylinder and earlier V8 models used only one standard universal joint. The torque tube design is typically heavier and securely ties the rear end together, thus providing for a rigid rear end and assuring good alignment under all conditions. However, because of the greater unsprung weight of the torque tube and radius rods, there may be a "little hopping around of the rear end when cornering fast or on washboard roads". Application Examples of the torque tube were the American cars of the Ford brand up through 1948, including over 19,000,000 Model Ts. Ford used the less expensive transverse springs that could not take forward thrust. For many of those years, Chevrolet used the torque tube, while Buick used it starting in 1906 (in the model D). The torque tube also allowed Buick, beginning in 1938, to use coil springs for a softer ride than traditional leaf springs, which can use a Hotchkiss drive, but coil springs cannot. Buick's use of a torque tube and coil springs