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THE CLUTCH
E
Fig. £.9
Checking
the
setting
of the
release
le>ers
illustrated by comparison between a pieoe of smoothly
finished wood
and
one with
a varnished
surface;
in
the
former the contact is
made directly
by the original
material, whereas in the
latter
instance
a
film of
dry
varnish is interposed between
the
contact surfaces
and
actual
contact
is
made
by
the
varnish.
If
the
clutch
has
been in use for some little time under
satisfactory conditions
the surface
of the
facings
assumes
a high polish through which the grain of the
material
can be
seen
clearly.
This
polished facing
is
of
light
colour
when
in
perfect condition.
Should
oil
in small quantities gain
access
to
t
he clutch
and
find its
way onto the
facings,
it will be burnt off as
a
result of
the
heat generated by the slipping occurring
under normal starting conditions. The burning of this
small quantity of lubricant
has
the effect of gradually
darkening the
facings, but,
provided the
polish
of the
faeiog remains such that
the
grain
of the
material can
be
distinguished clearly,
it bas
little
effect on clutch
per-
formance.
Should
increased quantities
of oil obtain access
to the
facing.
then
one of two
conditions,
or
a combination
of these,
may
arise, depending upon the
nature o
f
the oil.
MGA (Twin
Cam). Js.•ue
2. 27765
(
I)
The
oil may bum off and leave a carbon
deposit
on
the surface
of the
facings,
which
assume a
high glaze,
producing further
slip.
This
is a very
definite,
though very
thin,
deposit, and in general
it
bides
the
grain
of
the ml\lerial.
(2)
The
oil
may
partially
burn a nd
leave
a
resinous
deposit
on
the
facings. This
bas
a tendency
to
produce
a fierce
clutch,
and may
also cause
excessive
'spinning' due to the
tendency of the
face
of the
linings to adhere
to the
surface of
the
ftywheel or pressure plate.
(3)
There
may be
a
combination of
conditions
(I)
and
(2)
which
produces
a
tendency
to
'judder' on
~11ch
cn~gemenr.
Still
greater
quantities
of
oil
produce
a
dark
and
soaked appearance
of
the
facings,
and
the result will be
further slip, accompanied by fierceness
or
'j
udderiog'.
If the
conditions enumerated
above are
experienced,
the
clutch driven
plate should be replaced by
a
new one.
The
cause of the presence of the oil must
be
traced
and
removed.
It is,
of course,
necessary for the clutch and
ftywheel
to be
cleaned out
thoroughly before assembly.
Where the graphite release bearing
ring is badly
worn
in service a complete replacement assembly should
be
fitted, returning the
old assembly
for
salvage of the
metal
cup. These
graphite
rings are
inserted into
their
metal
cup by
heating the
metal
cup
to a cherry
red,
then forcing
the graphite
ring
into
position. Immediately the
ring is
forced
into
position the
whole
should
be quenched
in
oil. Alignment
of the thrust
pad in relation to its face
and the
trunnions should
be within ·005 in. (·12 mm.).
In
almost every case of rapid wear on the splines of
the clutch
driven
plate misalignment is
responsible.
Looseness
of the driven
plate on the splined
shaft
results
in
noticeable backlash
in
the
clutch. Misalign-
ment also
puts undue
stress on
the
driven
me
mber,
and
may
result in
the bub
breaking
loose from the plate, with
consequent
total
failure
of the
clutch_
It may also
be responsible for
a
fierce chattering
or
dragging of the
clutch, which
makes
gear changing
difficult- In cases
of
persistent
difficulty
it is advisable
to
check
the
ftywhecl for
truth
with
a
dial indicator.
The dial reading
should
not vary more
than ·003 in.
(
.07
mm.) anywhere
on
the
ftywheel
face.
£.9
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