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A torque tube system is a driveshaft technology, often used in automobiles with a front engine and rear drive. It is not as widespread as the Hotchkiss drive, but is still occasionally used to this day. Driveshafts are sometimes also used for other vehicles and machinery.
The "torque" that is referred to in the name is not that of the driveshaft, along the axis of the car, but that applied by the wheels. The design problem that the torque tube solves is how to get the traction forces generated by the wheels to the car frame. The "torque tube" transmits this force by directly coupling the axle differential to the transmission and therefore propels the car forward by pushing on the engine/transmission and then through the engine mounts to the car frame.
In contrast, the Hotchkiss drive has the traction forces transmitted to the car frame by using other suspension components such as leaf springs or trailing arms. A ball and socket type of joint called a "torque ball" is used at one end of the torque tube to allow relative motion between the axle and transmission due to suspension travel. Later AMC/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 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.
In addition to transmitting the 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. The 1963-66 AMC Rambler big cars use a double-Cardan constant velocity joint in V8 powered models 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 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"
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 to compete in cost, while Buick used it so as to be able to use coil springs for a softer ride than leaf springs.
Buick started using coil springs in the 1930s and used the torque tube as the main rear axle locating arm. This suspension design became a Buick "engineering trademark" until it was dropped with the 1961 model year full-sized models.
After the merger of Nash and Hudson, American Motors Corporation (AMC) continued to use the coil spring and torque tube rear suspension design on their large-sized cars (Rambler Classic and Ambassador) from the 1956 through the 1966 model year.
The Peugeot 403 and 404 models used a torque tube. The Peugeot 504, and Peugeot 505 estate/station wagons, as well as most export-market sedans also had torque tubes, while domestic and European-market sedan models had a transaxle and individual rear suspension.
The Chevrolet Chevette (1976-1988) used a torque tube and center bearing. This design was unlike any other Chevrolet model "to isolate impacts to the rear wheels, cut down on road noise, and reduce engine vibration ... also allows a reduction in the height of the drive shaft and tunnel."
The Mercedes SLS has a torque tube, but only to align the transaxle with the engine.
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403, 404, and 504 models use a torque tube driveshaft. This type of driveshaft consists of an outer tube which takes the thrust of the rear wheels which are in turn driven by an inner shaft
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