TM-5-3805-254-14-P-2
TRUCK, DUMP, 20 TON, 6X4, ON-OFF HIGHWAY 71,000 GVW, IHC MODEL F-5070 (CCE)
TECHNICAL MANUAL; OPERATOR’S, ORGANIZATIONAL, DIRECT SUPPORT, GENERAL SUPPORT AND DEPT MAINTENANCE MANUAL (INCLUDING REPAIR PARTS INFORMATION AND SUPPLEMENTAL MAINTENANCE INSTRUCTIONS)
JUNE 1980
TM-5-3805-254-14-P-2 - Page 578 of 894
INSTRUMENTS
MOTOR
TRUCK SERVICE MANUAL
SPEEDOMETER
The speedometer unit is only serviced complete and
includes the magnet, speedcup, cross gears and face
dial.
A speedometer is used on a vehicle to indicate
speed in miles per hour as shown by the pointer on face
dial and to record distance traveled by means of an
odometer.
The speedometer is driven through a flexible
shaft connected to a set of gears in the vehicle
transmission.
These gears are designed for the
particular vehicle model and take into consideration the
tire size and rear axle ratio.
The flexible shaft, which
connects the transmission driven gear to the
speedometer, consists of an outer casing and inner core.
The odometer records up to 99, 999.9 miles and
automatically returns to zero.
There are occasions when, due to change in axle
ratio or tire sizes, it is necessary to make compensating
corrections in the speedometer drive gear.
For method
of speedometer adapter calculations, see page 2 of this
section.
TACHOMETER
A tachometer is installed on a vehicle to record
engine RPM speeds and enable the driver to keep
engine within efficient operating range.
The magnetic type tachometer is driven by a flexible
shaft connected to the vehicle distributor shaft by means
of a drive joint or adapter and records the RPM from the
distributor shaft on the face dial through a magnetic
coupling within the unit.
There are two additional types of tachometers
available, namely, centrifugal, with a maximum RPM
hand, and electrical.
The centrifugal tachometer works on the weight-type
governor principle and is driven from the distributor shaft
in the same manner as the magnetic type.
The
centrifugal type also has a maximum RPM hand on the
tachometer head to record maximum speed of engine.
For diesel engines, the electric tachometer is a two-
unit combination consisting of a tachometer head and a
sender.
The head is mounted on the instrument panel
and the sender unit is mounted on the engine using the
tachometer drive take off.
SPEEDOMETER AND TACHOMETER CABLES
Two different types of speedometer and tachometer
drive cables have been used on IH vehicles.
They are
the flexible shaft (wrapped type cable) and the semi-rigid
types (covering of polypropylene or polyethylene on
cable).
The flexible shaft cable consists of two major
assemblies: a flexible outer casing
573
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