What component(s) allow(s) the operator to
operate the clutch?
What component(s) transfer(s) motion from the
release mechanism to the release bearing and
What component(s) within the clutch disc
absorb(s) vibration and shock produced by
What component prevents the engine starting
unless the clutch pedal is fully depressed?
If no service manual is available and an
adjustment of the clutch is required, what
amount of clutch pedal free travel will allow
adequate clutch operation?
Learning Objective: State the operating principles,
identify the components, and maintenance of a manual
A manual transmission is designed with two
purposes in mind. One purpose of the transmission is
providing the operator with the option of maneuvering
the vehicle in either the forward or reverse direction.
This is a basic requirement of all automotive vehicles.
Almost all vehicles have multiple forward gear ratios,
but, in most cases, only one ratio is provided for
Another purpose of the transmission is to provide
the operator with a selection of gear ratios between
engine and wheel so that the vehicle can operate at the
best efficiency under a variety of operating conditions
and loads. If in proper operating condition, a manual
transmission should do the following:
Be able to increase torque going to the drive
wheel for quick acceleration.
Supply different gear ratios to match different
engine load conditions.
Have a reverse gear for moving the vehicle
Provide the operator with an easy means of
shifting transmission gears.
Operate quietly with minimum power loss.
Before understanding the operation and power
flow through a manual transmission, you first must
understand the construction of the transmission. This
is necessary for you to be able to diagnose and repair
damaged transmissions properly.
The transmission case provides support for the
bearings and shafts, as well as an enclosure for
lubricating oil. A manual transmission case is cast
from either iron or aluminum. Because they are lighter
in weight, aluminum cases are preferred.
A drain plug and fill plug are provided for
servicing. The drain plug is located on the bottom of
the case, whereas the fill plug is located on the side.
Also known as the tail shaft, the extension
housing bolts to the rear of the transmission case. It
encloses and holds the transmission output shaft and
rear oil seal. A gasket is used to seal the mating
surfaces between the transmission case and the
extension housing. On the bottom of the extension
housing is a flange that provides a base for the
Front Bearing Hub
Sometimes called the front bearing cap, the
bearing hub covers the front transmission bearing and
acts as a sleeve for the clutch release bearing. It bolts to
the transmission case and a gasket fits between the
front hub and the case to prevent oil leakage.
A manual transmission has four steel shafts
mounted inside the transmission case. These shafts are
the input shaft, the countershaft, the reverse idler shaft,
and the main shaft.
INPUT SHAFT.The input shaft, also known as
the clutch shaft, transfers rotation from the clutch disc