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THE OVERDRIVE

Section

Fa.1

LUBRICATION

The

overdrive

common

oil

supply

with the

gearbox;

■lled and

topped

through the gearbox

dipstick

hole and

the oil

level

checked

with the

gearbox

dipstick.

Draining

When

overdrive

■tted,

remove

the

overdrive drain

plug

marked

‘DRAIN’

and the gearbox

drain

plug,

and drain

off

the old oil.

Remove

the

overdrive

■lter

cover-plate and

gasket

from the

left-hand

side

of the

unit

and

withdraw

the

■lter

gauze,

together

with the

■lter

seal and

magnetic

rings.

Wash the

gauze

fuel

and clean

out

the

filter housing.

Clean

the

■lter seal and

remove

all

deposits

from

the

magnetic

rings.

Replace

the

■lter seal

(metal

surface

inwards)

and

place the

magnetic

rings in

the

■lter location.

Re■t

the

■lter, gasket,

and

cover-plate,

replace

the drain

plugs, and

refill with fresh

oil.

Check

the filter

cover-plate and

drain plug

for leaks.

Section Fa.2

DESCRIPTION

The

overdrive

unit

comprises

hydraulically

controlled

epicyclic

gear

housed

casing

which

directly

attached

extension

the

rear

the gearbox.

The gearbox

third

motion

shaft

extended and

carries

its

end

the

inner

member

uni-directional

clutch. The

outer

ring

the

clutch

carried

the

combined annulus

and

output

shaft.

Also

mounted

the

third

motion

shaft

are

the

planet

carrier

and

freely

rotatable

sun

wheel, and sliding

thereon

cone

clutch member

the

inner

lining of which

engages

the

outside of the

annulus

while the

outer

lining

engages

cast-iron

brake

ring

sandwiched between

the

main

and tail

casings.

The

cone

clutch

held

contact

with the annulus by

compression

springs,

thus

locking the

sun

wheel

the

annulus

that

the

entire

gear

train

rotates

as a

solid

unit,

A9195

Fig. Fa.1

Direct

am.

Cone

clutch.

Uni-directional clutch.

Spring

pressure.

Third

motion

shaft.

3. Sun

wheel.

Fa.4

giving

direct drive. In

this condition

the drive

taken

through the

uni-directional clutch.

Reverse

torque

overrun

taken by

the

planet

wheels,

which

being

locked

the

sun

wheel,

transmit

the

drive

via

the planet

carrier

and

third

motion

shaft.

Hydraulic

pressure

produced when

overdrive

selected

forces

two

pistons

the

unit

housing

against

the

cone

clutch

and

overcomes

the

spring

pressure,

causing

the

cone

clutch

engage

with the

stationary

brake

ring

and bring

the

sun

wheel

to rest,

allowing the annulus

overrun

the

uni-directional

clutch and

give

increased speed

the

output

shaft,

i.e.

‘overdrive’.

When changing from overdrive

direct

gear,

if the

accelerator pedal

released the

vacuum

switch

holds

‘overdrive’ until the engine

takes

the

drive.

If the

accelerator

pedal

not

released, when

contact

between

the

cone

clutch and brake

broken,

the

unit

still

operates

momentarily

in its

overdrive

ratio

engine

speed

and road

speed

remain

unchanged.

When the load

the

engine is

released

begins

accelerate, speeding

the

sun

wheel

from

rest

until,

just

the

instant

when

its

speed

synchronizes with

the speed of the annulus,

the whole

unit

revolves solidly and

the uni-directional

clutch takes

the

drive

once more.

The

movement

of the

cone

clutch

deliberately slowed

down

that

the uni—directional clutch

driving

before the

cone

clutch

contacts,

ensuring

perfectly synchronized

change.

Section Fa.3

CONSTRUCTION

The

third

motion

shaft of the gearbox

extended

carry

first

a cam

operating

the oil

pump

and

then

steady

bearing

with

plain'

phosphor-bronze bush carried

the

main

housing. Next

the

sun

wheel of the epicyclic

gear

carried

Clevite bush,

and behind this the

shaft

splined

take

the planet

carrier

and

uni-directional clutch.

The

end of the shaft

reduced

and

carried

needle-roller bearing

the

output

shaft. The latter

supported

the

rear

housing by

two

roller bearings.

The

clutch member slides

the splines of

the

sun

wheel

Fig. Fa.2

Overdrive

engaged

4. Planetcarrier.

Annulus.

Hydraulic

pressure.

2. Brake ring.

3. Planet

wheel.

MGB.

Issue

65891

Brand	MG
Model	MGB
Category	Automobile
Language	English

MG MGB User Manual

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MG MGB Specifications

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