magnet to trap the metal particles produced as the trans-
mission components wear. Oil pans are usually made of
sheet metal. A few pans are made of cast aluminum.
Bushings and Bearings
Bushings and bearings allow parts to move against
each other with minimal friction. Bushings, Figure 1-25,
provide a sliding contact with the moving part and require
good lubrication. They are installed where rotating part
passes through a stationary part or two rotating parts are in
contact with each other.
Ball bearings or roller bearings provide a rolling con-
tact for reduced friction. Bearings are usually used where
there is a heavy load, such as the output shaft, or an inter-
nal part that is subjected to high pressure. Thrust bearings
are used in other places where parts are rotating in relation
to each other under heavy pressures. A thrust washer sep-
arates moving parts, but it is made of a single piece of flat
metal. Some thrust washers are available in different
thicknesses and are used to adjust transmission shaft back-
and-forth movement, or endplay. Typical roller bearings,
thrust bearings, and washers are shown in Figure 1-26.
Hydraulic Pump and Pressure Regulator
The hydraulic pump provides all the hydraulic pres-
sure used in the automatic transmission or transaxle. An
extension at the rear of the torque converter drives the
pump on transmissions. A separate shaft attached to the
converter is often used to drive transaxle oil pumps.
Whenever the engine is running, the converter is turning
and causing the pump to turn. Therefore, whenever the
Chapter 1 Introduction to Automatic Transmissions and Transaxles 23
Figure 1-23. A one-way clutch assembly. Note how each roller
fits into a ramp on the inside of the outer gear. This design
permits the internal roller to rotate in one direction but locks it
when it tries to turn the other way.
Figure 1-24. Common transmission and transaxle case
designs are shown here. Power enters the transmission case at
the front and exits at the rear. Power enters the transaxle case at
the engine connection and exits in two directions. A few
transaxles are designed so power exits in only one direction.
Figure 1-25. The average transmission or transaxle contains many bushings to support moving parts. Bushings may be installed
between the case and a moving shaft, or between two turning parts. (General Motors)