MG MGB User Manual

THE OVERDRIVE
Fa
extension
to
contact
either the annulus
or
the
cast-iron
braking
ring
forming
part
of the
unit
housing.
A
ball
bearing
housed
in
a
■anged
ring
is
secured
to
the
cone
clutch member.
This
carries
four
bolts which
act
as
guides
to
compression springs
by which the
ring,
and with
it
the clutch
member,
is
held
against
the
annulus. The
action
of the
springs
prevent
free-wheeling
on
overrun
and they
are
of suf■cient
strength
to
handle
reverse
torque.
Also
secured
to
the four
bolts
are
two
bridge
pieces
against
which
bear
two
pistons
operating in
cylinders formed
in
the
unit
housing.
The cylinders
are
connected
by
ports
in
the
hydraulic
system
to
a
relief
valve which
regulates
the
pressure
developed
by the oil
pump.
When
the valve
is
open
(overdrive
selected),
oil
under
pressure
is
admitted
to
the
cylinders and
pushes the
pistons
forward
to
engage
the
overdrive
clutch.
Closing
the valve
cuts
off the
supply of
oil
to
the
cylinders
and allows
it
to
escape.
Under the in■uence
of
the
springs
the
clutch
member
moves
back
to
engage
direct drive
position.
The
escape
of oil from
the
cylinders
is
deliberately
restricted
so
that the
clutch
takes
up
slowly.
The
sun
wheel
and
pinions
are
case—hardened
and the
annulus
heat-treated.
Gear teeth
are
helical.
The
pinions
have
needle-roller
bearings and
run on
case-hardened
pins.
The
outer
ring
of
the
uni-directional
clutch
is
pressed
into
the annulus
member. The clutch itself
is
of the
caged roller
type,
loaded by
a
lock-type
spring
made of
round
wire.
The
hydraulic
system
is
supplied
with oil by
a
plunger-type
pump
operated by
a cam on
the
gearbox third
motion
shaft. The
pump
body
is
pressed
into
the
main
housing
and
is
located by
a
grub
screw.
The
pump
delivers oil
through
a
non-return
valve
to
a
relief
valve,
in
which
a
piston
moves
back
against
a
compression spring
until the
required
pressure
is
reached,
at
this
point
a
hole
in
the
relief
valve
is
uncovered. The spill oil
from
the
relief
valve
is
led through
l
i
37
,.
/.
,
$1?
3%
5%.,
’~..,, 31659A
Fig. Fa.3
Hydraulic system—direct
drive
1.
Operating
cylinders. 4.
Jet.
2.
Cam.
5.
Operating
linkage.
3. Operating
valve.
MGB.
Issue4. 65891
drilled
passages
to
an
annular
groove
in
the
steady bush
on
the third
motion
shaft.
Radial holes
in
the shaft
collect
oil
and deliver
it
through
an
axial drilling
to
other radial
holes
in
the shaft from
which
it is
fed
to
the
needle-roller
bearing,
thrust
washer, and
uni-directional
clutch,
and
is
led
to
the
planet
gear
pins
by
a
thrower
attached
to
the planet
carrier.
When ‘Overdrive’
is
selected the valve
is
lifted,
thus holding
the
ball
off
its
seat
against
the
spring
pressure
of
the
plunger
spring.
Oil
passes
to
the
operating
cylinders, forcing
the
pistons
forward
to
engage
the
overdrive clutch.
With the
selection
of
‘Normal’
drive
the
spring
plunger
pushes the
ball
onto
its
seat
and the valve falls
away
from
the ball. Oil
from
the
cylinders then
returns
through
the
centre
of
the
valve
to
the
sump.
Near
the bottom of the
valve
is
a
small
jet
which
slows
down the
emptying
of the
cylinders,
to
provide smooth
re-engagement
of
direct drive.
For direct
drive the
oil
is returned
to
the
sump
via
the
operating
valve and ■ows
in
open
circuit
(Fig.
Fa.3).
Section Fa.4
GUIDE
TO SERVICE
DIAGNOSIS
Overdrive
does
not
engage
]
.
Insuf■cient
oil
in
the
unit.
2. Solenoid
not
operating
due
to
fault
in
electrical
system.
Solenoid
operating lever
out
of
adjustment.
4.
Insuf■cient
hydraulic
pressure
due
to
DJ
Pump
non-return
valve
incorrectly
seating
(probably
dirt
on
ball
seat).
>\\\\
a
nut-1o.
’m‘
BIBSBA
Fig.
Fa.4
Hydraulic
system
—overdrive
1.
Oil
pump.
5. Axial drilling—third
motion
2. Oil inlet.
shaft.
3. Non-return
valve.
6.
Third
motion
shaft
steady
4.
Oil
relief
valve.
bush.
Fa.5

MG MGB Specifications

General

Brand	MG
Model	MGB
Category	Automobile
Language	English