MG MGB User Manual

E
THE
CLUTCH
Section E2
SERVICING
THE
CLUTCH
Driven plates
It
is important that
neither
oil
nor
grease
should
contact
the clutch
facings.
It
is
essential
to
install
a
complete
driven
plate
assembly
when the
renewal
of
the friction
surfaces
is required. lf
the
facings
have
worn
to
such
an
extent
as
to warrant
renewal,
then slight
wear
will have
taken
place
on
the splines,
and
also
on
the
torque
reaction springs and their
seatings.
The
question
of
balance
and
concentricity
is
also
involved.
Under
no
circumstances
is it
satisfactory
to
repair
or
rectify
faults
in
clutch driven
plate
centres.
Tolerances
Wear
on
the working faces
of
the
driven plate
is
about
.001
in.
(.02
mm.)
per
1,000
miles (1600
km.)
under
normal
running
conditions.
The
accuracy
of
the alignment
of
the
face
of the
driven
plate
must
be
within
.015
in.
(.38
mm.).
Condition
of clutch facings
in
service
It
is
natural
to
assume
that
a
rough surface
will
give
a
higher
frictional
value
against slipping than
a
polished
one,
but this
is
not
necessarily
correct.
A
roughened
surface
consists
of
small
hills'and
dales,
only the
‘high-spots’
of
which
make
contact.
As the
amount
of
useful friction
for
the
purpose
of
taking
up
the
drive
is
dependent
upon
the
area
in actual
contact,
it is
obvious
that
a
perfectly
smooth
face
is
required
to
transmit
the
maximum
amount
of
power
for
a
given
surface
area.
Since non-metallic facings
of the
moulded
asbestos
type
have
been introduced
in service
the
polished
surface
is
common,
but
it
must not
be confused
with
the
glazed
surface
which
is
sometimes encountered due
to
conditions
to
be detailed
subsequently.
The
ideally
smooth
or
polished
condition
will therefore
provide
proper
surface
contact,
but
a
glazed surface
entirely alters the frictional
value of
the
facing
and
will result
in
excessive
clutch
slip.
These
two
conditions might
be
simply illustrated
by
comparison
between
a
piece
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
■lm
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
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
the
clutch
and
■nd
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
facing
remains
E.4
such
that
the
grain
of the
material
can
be
distinguished
clearly,
it
has
little
effect
on
clutch
performance.
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
of
the
oil.
1. The
oil
may
burn off
and leave
a
carbon
deposit
on
the
surface
of
the facings,
which
assume
a
high
glaze,
producing
further
slip.
This
is
a very
de■nite,
though
very
thin,
deposit,
and
in general
it
hides
the
grain
of
the
material.
2. The
oil
may
partially
burn
and leave
a
resinous
deposit
on
the facings.
This has
a
tendency
to
produce
a
■erce
clutch,
and
may
also
cause
excessive
‘spinning’
due
to
the
tendency
of
the face
of
the linings
to
adhere
to
the
surface
of
the ■ywheel
or
pressure
plate.
3.
There
may
be
a
combination
of
conditions
1 and
2
which
produces
a
tendency
to
‘judder’
on
such
engagement.
Still
greater
quantities
of
oil
produce
a
dark
and soaked
appearance
of
the facings,
and the
result
will be further
slip,
accompanied by ■erceness
or
‘juddering’.
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
■ywheel
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
positionflmmediately
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.
Misalignment
also
puts
undue
stress
on
the
driven
member,
and
may
result
in the
hub
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
dif■cult.
in
cases
of
persistent
dif■culty
it
is
advisable
to
check
the flywheel
for
truth
with
a
dial
indicator.
The
dial
reading
should
not
vary
more
than
.003
in.
(.07
mm.)
anywhere
on
the
■ywheel
face.
Section
E.3
MASTER
CYLINDER
The
master
cylinder
has
an
integral-type
supply
tank
in
which
the
barrel
passes
through
the
tank.
A
piston
contained
within
the
barrel
has
a
rubber
main
cup
and
is
spring-loaded
against
its inner end;
between
the
piston and
cup
is
a
thin
washer
which
prevents
the
cup
being
drawn
MGB.
Issue4.
15676

MG MGB Specifications

General

Brand	MG
Model	MGB
Category	Automobile
Language	English