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352
FIAT· 850 PASSENGER CARS
Fig. 570 • Plunger valve solenoid.
a progressive clutch operation and to act as a
safety device when changing down at excessively
high road speeds.
In
fact, during downshifts the clutch is disen-
gaged; the driven plate rotates faster than the bell
housing
I
thereby causing a pressure increase within
chamber
C
which opposes pressure in B and the
action of the disc spring.
The higher the driven plate speed,
with
respect
to the bell housing. the greater will be the pressure
build-Up within chamber C and the increase in
differential between higher pressure in C and static
pressure in
B
which tends to engage the clutch.
Consequently
I
a longer delay will occur on en-
gagement.
Naturally
I
this delay
will
be just about noticeable
when, after engaging a lower gear
I
the speed
(I.p.m.) at which the engine is driven
by
the road
wheels is within the specified limits.
Also to be borne in mind is the fact that the above
delay occurs during coasting only.
In fact, under
pull the depression of the accelerator on the part
of the driver soon after change-down has occur-
red, causes the valve on the driven plate to move,
thereby uncovering the partialiser orifice and at
the same time reducing or eliminating the speed
differential between bell housing and driven plate,
i.e., the dynamic pressure.
At this point the static pressure immediately over-
comes the dynamic pressure thus enabling the
clutch to engage.
This is particularly useful when
changing down in order to obtain a brisker pick-up
for overtaking.
OPERATION
OF ELECTRICAL SYSTEM
The electrical system consists of a relay, an inhib-
itor switch, a solenoid, a neutral switch and a
knob switch fitted at the top of the gear selector
lever.
Relay (3, fig. 571), controls solenoid (5) which,
in turn, operates plunger valve; switch (4) acts
as an inhibitor monitoring starter motor relay (9).
Neutral switch (6) is closed when selector lever
is in
neutral position and open with the transmis-
sion in gear.
Knob switch (7) is normally open
and closes when the driver grips the selector lever
knob.
IA~
TF~>-J----
1j)f;
1
I--
..
-
,
J~
I
7
6
i0
B
~
-rn-
.-
•
Fig. 511 - Wiring diagram.
1. Selector switch.· 2. 8-Amp fuse. - 3. Solenoid relay. - 4. Starter motor inhibitor switch.· 5. Plunger valve solenoid for clutch control
6. Neutral switch. - 7. Knob switch on gear selector lever•• 8. Starter motor. - 9. Starter motor relay,
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