The internal components of
a transmission or transaxle consist of a parallel set of metal shafts on
which meshing gearsets of different ratios are mounted. By moving the
shift lever, gear ratios can be selected to generate different amounts
of output torque and speed.
The gears are mounted or
fixed to the shafts in a number of ways. They can be internally splined
or keyed to a shaft. Gears can also be manufactured as an integral part
of the shaft. Gears that must be able to freewheel around the shaft
during certain speed ranges are mounted to the shaft using bushings or
The shafts and gears are
contained in a transmission or transaxle case or housing. The components
of this housing include the main case body, side or top cover plates,
extension housings, and bearing retainers. The metal components are
bolted together with gaskets providing a leak-proof seal at all joints.
The case is filled with transmission fluid to provide constant
lubrication and cooling for the spinning gears and shafts.
Although they operate in a
similar fashion, the layout, components, and terminology used in
transmissions and transaxle are not exactly the same.
A transmission has three
specific shafts: the input shaft, the countergear shaft, and the
mainshaft or output shaft. The clutch gear is an integral part of the
transmission's input shaft and always rotates with the input shaft.
The counter gear is
actually several gears machined out of a single piece of steel. The
counter gear may also be called the countergear or cluster gear. The
counter gear mounts on roller bearings on the countershaft. The
countershaft is pinned in place and does not turn. Washers control the
amount of end play of the unit in the transmission case.
The main gears on the main
shaft or output shaft transfer rotation from the counter gears to the
output shaft. The main gears are also called speed gears. They are
mounted on the output shaft using roller bearings. Speed gears freewheel
around the output shaft until they are locked to it by the engagement of
their shift synchronizer unit.
Power flows from the
transmission input shaft to the clutch gear. The clutch gear meshes with
the large counter gear of the counter gear cluster. This cluster gear is
now rotating. Since the cluster gear is meshed with the speed gears on
the mainshaft, the speed gears are also turning.
There can be no power
output until one of the speed gears is locked to the mainshaft. This is
done by activating a shift fork, which moves its synchronizer to engage
the selected speed gear to the mainshaft. Power travels along the
counter gear until it reaches this selected speed gear. It then passes
through this gear back to the mainshaft and out of the transmission to
Transaxles use many of the
design and operating principles found in transmissions. But because the
transaxle also contains the differential gearing and drive axle
connections, there are major differences in some areas of operation.
This transaxle uses fully synchronized, constant mesh helical gears on
all forward speeds and spur gears for reverse.
A transaxle has two
separate shafts - an input shaft and an output shaft. The input shaft is
the driving shaft. It is normally located above and parallel to the
output shaft. The output shaft is the driven shaft. The transaxles main
(speed) gears freewheel around the output shaft unless they are locked
to the shaft by their synchronizer assembly. The main speed gears are in
constant mesh with the input shaft drive gears. The drive gears turn
whenever the input shaft turns.
The names used to describe
transaxle shaft vary between manufacturers. The service manuals of some
vehicles refer to the input shaft as the mainshaft and the output as the
driven pinion or drive shaft. Others call the input shaft and its gears
the input gear cluster and refer to the output shaft as the mainshaft.
For clarity, this text uses the terms input gear cluster for the input
shaft and its drive gears, and pinion shaft for the output shaft.
A pinion gear is machined
onto the end of the transaxle's pinion shaft. This pinion gear is in
constant mesh with the differential ring gear located in the lower
portion of the transaxle housing. Because the pinion gear is part of the
pinion shaft, it must rotate whenever the pinion shaft turns. With the
pinion rotating, engine torque flows through the ring gear and
differential gearing tot he drive shafts and driving wheels.