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The drive shaft, or propeller shaft, connects the transmission output
shaft to the differential pinion shaft. Since all roads are not
perfectly smooth, and the transmission is fixed, the drive shaft has
to be flexible to absorb the shock of bumps in the road. Universal,
or "U-joints" allow the drive shaft to flex (and stop it from
breaking) when the drive angle changes.
Drive shafts are usually hollow in order to weigh less, but of a
large diameter so that they are strong. High quality steel, and
sometimes aluminum are used in the manufacture of the drive shaft.
The shaft must be quite straight and balanced to avoid vibrating.
Since it usually turns at engine speeds, a lot of damage can be
caused if the shaft is unbalanced, or bent. Damage can also be caused
if the U-joints are worn out.
There are two types of drive shafts, the Hotchkiss drive and the
Torque Tube Drive. The Hotchkiss drive is made up of a drive shaft
connected to the transmission output shaft and the differential
pinion gear shaft. U-joints are used in the front and rear. The
Hotchkiss drive transfers the torque of the output shaft to the
differential. No wheel drive thrust is sent to the drive shaft.
Sometimes this drive comes in two pieces to reduce vibration and make
it easier to install (in this case, three U-joints are needed).The
two-piece types need ball bearings in a dustproof housing as center
support for the shafts. Rubber is added into this arrangement for
noise and vibration reduction.
The torque tube drive shaft is used if the drive shaft has to carry
the wheel drive thrust. It is a hollow steel tube that extends from
the transmission to the rear axle housing. One end is fastened to the
axle housing by bolts. The transmission end is fastened with a torque
ball. The drive shaft fits into the torque tube. A U-joint is located
in the torque ball, and the axle housing end is splined to the pinion
gear shaft. Drive thrust is sent through the torque tube to the
torque ball, to transmission, to engine and finally, to the frame
through the engine mounts. That is, the car is pushed forward by the
torque tube pressing on the engine.
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