Seat FIAT 500 1964 1.G Owner's Manual

indicates the condition inside the combustion chamber
and may be used as a guide to engine tuning.
Before the spark plugs are removed b l o w away any
loose dirt from the plug recesses using a compressed air
jet or tyre pump. Store the plugs in the order of removal
ready for inspection.
Examine the gaskets and if they are about half their
thickness they may be used again otherwise they must be
replaced.
Inspect the electrode end of the plugs and note the
type and colour of the deposit. Normally it should be
powdery and range from b r o w n to a greyish tan in colour.
There will also be slight wear of the electrodes and the
general effect described is one which comes from mixed
periods of high-speed and low-speed driving. Cleaning
and resetting the gap is all that will be necessary.
If the deposits are white or yellowish they indicate long
periods of constant-speed driving or much low-speed
city driving. Again, the treatment is straightforward.
Dry, black, fluffy deposits are usually the result of
running with too rich a mixture. Incomplete combustion
of the petrol air charge may also be a cause and this might
be traced to a defect in the ignition system or excessive
idling.
Overheated sparking plugs have a white blistered look
about the centre electrode and the side electrode may be
badly eroded. This may be caused by poor cooling, wrong
ignition timing or sustained high speeds under heavy load.
To clean the sparking plugs effectively they should be
cleaned using an abrasive blasting machine and tested
under pressure once the electrodes have been reset. File
these until they are clean, bright and the faces parallel and
set the gap to .019 to .023 inch. Do not try to bend the
centre electrode.
Before replacing the plugs use a wire brush to clean the
threads taking care that the electrodes are not touched.
Thoroughly clean the spark plug in petrol, and dry using a
compressed air jet or a tyre pump. If difficulty is found in
screwing the plugs into the cylinder head by hand run a
tap d o w n the threads to clear away any carbon. If a tap is
not available use an old sparking plug with crosscuts d o w nthe threads. Finally tighten the plugs to a torque wrench
setting of 18 to 21 Ib ft.
Sparking plug leads:
The spark plug leads and the lead from the coil to the
distributor cap must be regularly checked for cracking of
the insulation and also correct seating in the distributor
cap and coil top. It is recommended that silicone grease is
smeared around the sockets before the leads are replaced
to ensure no moisture may enter causing difficult starting.
3 : 9 The distributor driving spindle (sedan and
sports engine)
If for any reason, the driving spindle has been removed
from its housing in the crankcase, it must be correctly
meshed w i t h the camshaft gear otherwise it
will be impos-
sible to set the ignition timing.
3:10 Fault diagnosis
(a) Engine w i l l not fire
1 Battery discharged
2 Distributor contact points dirty, pitted or maladjusted
3 Distributor cap dirty, cracked or tracking
4 Carbon brush inside distributor cap not touching rotor
5 Faulty cable or loose connection in low-tension circuit
6 Distributor rotor arm cracked
7 Faulty coil
8 Broken contact breaker spring
9 Contact points stuck open
(b) Engine misfires
1 Check 2, 3, 4, and 7 in (a)
2 Weak contact breaker spring
3 High-tension plug and coil leads cracked or perished
4 Sparking plug(s) loose
5 Sparking plug insulation cracked
6 Sparking plug gap incorrectly set
7 Ignition timing too far advanced

CHAPTER 4
THE COOLING SYSTEM
4:1
4:2
4:3Description
Air outlet thermostat and shutter
Tension adjustment4:4
4:5
4:6Heating system safety device
Maintenance
Fault diagnosis
4:1Description
Sedan:
A l l the Fiat new 500 models covered by this manual are
aircooled by the forced air circulation system from a
centrifugal blower which is mounted on the generator
output shaft. The blower fan has fourteen vanes which are
arranged at various angles to reduce operating noise
during high-speed operation. A specially designed
cowling as shown in FIGS 4 : 1 and 4:2 conveys the air
from the blower and distributes it to the various parts of
the exterior of the engine.
The main components of the air cooling system are as
follows:
1 Air intake compartment at the rear end of t h e body.
2 An elbow pipe for the admittance of incoming air.
3 A flexible air pipe connecting the elbow pipe to the
conveyor.
4 A spiral air conveyor which contains the centrifugal fan.
5 Distribution ducting for directing the air flow to various
parts of the engine.
6 A bellows type thermostat is fitted to the cowling which
operates a butterfly shutter controlling the air outlet
from the engine which ensures control of the engine
operating temperature.
F50053 When the shutter is in the open position, engine heated
air is allowed to disperse to the outside of the engine
cowling. With the shutter in its closed position, the air is
recirculated in the engine cowling so ensuring a quick
engine warm-up period.
It should be noted that by operating the heater lever
which is located on the centre tunnel at the rear seat,
warmed air flowing out from the engine cowling is passed
to the inside of the car for heating and demisting purposes.
Station wagon:
Refer to FIG 4 : 2 where it will be seen that as the engine
is located on its side underneath the luggage compartment
floor the ducting has been modified and the air intakes are
located at the rear of the side windows. A linear blower is
housed in the engine baffles and cowling and is attached
to the drive end of the generator.
The thermostat 'C' (see FIG 4 : 2) is located on the
righthand side of the engine cowling and should start
opening the engine heated air outlet shutter ' D ' when the
temperature of the air rises to 1 7 8 - 1 8 5 ° F and the shutter
should be wide open when the air is at a temperature of
196-207°F.

OIL DRAIN PLUG COOLING AIR DUCTS
FIG 4 : 3 Oil sump with blower cowling. Arrows indicate
air outlets
BLOWER
SHAFT GENERATOR ARMATURE
VENT TUBE
FIG 4 : 4 Cooling blower mounted on generator shaft
extension
4 : 2 Air outlet thermostat and shutter
Refer to FIGS 4 :1 and 4 :2 where it will be seen that
the thermostat is located on the righthand side of the
engine cowling. The thermostat should start opening the
engine heated air outlet shutter when the temperature of
the air reaches between 158-165°F (178-185°F station
wagon) and the shutter should be in the wide open posi-
tion when the air has reached a temperature of between
178-189°F (196-207°F station wagon).
When the engine cooling air control system is being
inspected or serviced the following points should be
noted:
1 Check that when the shutter is in the closed
position the edge mates perfectly with the cowling
seating.
2 Ensure that the shutter can swivel freely.
3 Check that the initial thermostat movement is
between .0197 to .0394 inch.
4 Generally check the engine cowling for distortion, bad
jbint sealing or cracks.
56
Key to Fig 4 : 6 1 Circular seat i n cylinders 2 Head
ducts 3 Pierced screws
FIG 4 : 6 Diagram of the heating system safety device
(sedan and station wagon) FIG 4 : 5 Location of cooling air outlet thermostat and
shutter
ENGINE COWLING.
THERMOSTAT
LINK
AIR OUTLET SHUTTER
SHUTTER RETURN SPRING
4 : 3 Tension adjustment, thermostat to shutter
link:
The tension may be varied by using the shims which are
located between the upper shank of the thermostat and
the cover shoulder washer. Before any adjustment is made
ensure that the shutter is able to move freely and that the
return spring has not stretched or fractured. Refer to
FIG 4:5 which shows the location of the shutter and the
return spring.

4 : 4 Heating system safety device
110F series sedan engines and later station wagon
engines incorporate a modification to the cylinder head
designed so that in the event of cylinder head gasket
failure exhaust gases are expelled outside the engine and
not leaked into the heating system.
The safety device comprises a square section circular
seat 1 (see FIG 4 :6) which is formed in the upper face of
the cylinder, a special duct in the cylinder head and a
pierced screw 3 for each cylinder.
The system is so designed that the exhaust gases are
released to the atmosphere from the circular seat in the
cylinder via the duct 2 and the pierced screw 3. It should
be noted that the screw 3 is also used for securing the
conveyor.
4 : 5 Maintenance
Due to the simple design of the air cooling system
maintenance has been kept to an absolute minimum and
should consist of the following checks:1 Inspect all the air conveyor system joints and ensure
that all the joint nuts and bolts are tight and that there
is no distortion between two joint faces.
2 Check that the tension of the generator and fan drive
belt is correct: with a hand pressure of approximately
22 Ib the belt should sag 13/32 inch. Adjust if necessary
as detailed in Chapter 1.
3 Ensure that the shutter can swivel freely and that the
spring is in a serviceable condition.
4 : 6 Fault diagnosis
(a) Engine overheating
1 Generator and fan drive belt slipping
2 Shutter control thermostat defective
3 Shutter unable to swivel freely
4 Shutter return spring broken
5 Leaking joints in conveyor system
F50057

*Dimension to be obtained by
adjusting the throwout lever.
FIG 5:1 Clutch assembly longitudinal section (new
500, 500D sedan and early station wagon)
5 : 2 Removal and installation
To remove the clutch unit from the vehicle proceed as
follows:
1 Remove the engine (Chapter 1) or separate the gear-
box from the engine as described in Chapter 6.
2 Remove the six screws and washers that secure the
clutch cover to the flywheel and gently ease the cover
assembly from the location dowels in the flywheel and
lift away. This will also free the driven plate.
3 Carefully clean the driven plate and clutch cover using a
compressed air jet.
4 To refit the clutch cover assembly to the flywheel
ensure that the driven plate is assembled the correct
way round as shown in FIG 5 :1 and place the cover
onto the flywheel using the locating dowels.
5 To ensure that the driven plate is correctly centred use
Fiat pilot A.62023 (see FIG 5 : 5) or a suitably sized
mandrel. Tighten the clutch mounting screws diagonally
a turn at a time to ensure correct location of the cover
onto the flywheel face. Finally, tighten to a torque
wrench setting of 5.8 to 7.2 Ib ft.
5 :3 Dismantling and inspection of clutch cover
New 500, 500D sedan and early 500 station wagon :
To dismantle the clutch cover assembly proceed as
follows:
60
To assemble the clutch cover assembly proceed as
follows:
1 Place the pressure plate complete with carrier ring bolts
and springs on Fiat fixture 62038 (see FIG 5 : 2).
2 Fit the six pressure springs in their respective seats on
the pressure plate. Insert the cups on the springs and
replace the cover.
3 Compress the clutch cover, continually checking that
the withdrawal lever supporting bolts are properly
guided into their holes in the cover. Onto the bolts, fit
the three withdrawal levers w i t h their relevant nuts and
washers.
4 Replace the carrier ring on the levers and hook up the
retaining springs. 5 :4 Assembly and adjustment
N e w 500 sedan1 Place the clutch cover assembly on Fiat fixture A.62038
as shown in FIG 5 :6 and lock the cover using the three
T-handles provided.
2 Release the w i thdrawal lever carrier ring springs and lift
away the ring.
3 Unscrew the withdrawal lever fixing nuts on the bolts
and lift out the levers and washers. Gradually slacken
the three T-handles so relieving the pressure of the
clutch springs. Remove the clutch cover, springs and
lever mounting bolts. Carefully mark all the components
to ensure that they are assembled correctly so ensuring
that correct balance of the clutch unit is obtained.
Inspection:
Thoroughly clean all parts using a compressed air jet
and proceed as follows:
1 Thoroughly check the springs for signs of overheating
causing loss of tension and compare the effective length
of the springs which when fitted new should have a
length of .9646 inch under a load of not less than 43 Ib.
If the spring length is less t h a n t h e recommended
dimension fit a complete new set of springs.
2 The length of the withdrawal lever carrier ring retaining
springs should be checked which under a normal clutch
load should be .7677 inch whilst the length'of the
expanded spring under a load of 4.85 ± .44 Ib should
be 1.1811 inch. If the springs show sign of heating or
weakening a new set should be fitted.
3 Check the withdrawa l levers and their bolts for exces-
sive wear and fit new parts as necessary.
4 Inspect the pressure plate for an excessively ridged sur-
face or signs of cracking. If the ridges are not too severe
the face may be refaced by turning on a centre lathe.
Also inspect the flywheel friction surface which may
also be refaced providing that the ridges are not too
severe.
5 Whenever the clutch driven plate linings are worn a new
driven plate should be fitted.
6 Inspect the clutch shaft splines and these should not
have a lengthwise clearance in excess of .0039 inch and
side clearance of .0118 inch w i t h respect to the driven
plate hub. Ensure that the driven plate slides easily on
the clutch shaft protruding from the rear of the gearbox
differential unit as any plate drag may be the cause of
d i f f i c u l t y in gear selection.

PRIMARY SHAFT-TO-CLUTCH
SHAFT MOUNTING PINCLUTCH SHAFT SEAL PRIMARY SHAFT WITH
1st, 3 r d A N D 4 t h SPEED
GEAR CLUSTER
2 n d SPEED
DRIVE GEARPRIMARY SHAFT
FRONT BALL BEARINGPRIMARY SHAFT
REAR BALL BEARING
PRIMARY
SHAFT-TO-CLUTCH
i SHAFT JOINING SLEEVEJOINING SLEEVELOCKRING
SPEED SELECTOR LEVER
CLUTCH SHAFT
LAYSHAFT WITH BEVEL PINION
SPEEDOMETER DRIVE GEAR
2 n d SPEED ENGAGEMENT
SLIDING SLEEVE
2 N D SPEED DRIVEN GEAR
LAYSHAFT FRONT BALL
BEARING
3 r d SPEED DRIVEN GEARHUB FOR
SLEEVE
3rd AND 4th/
SPEED ENGAGEMENT
SLIDING SLEEVE4 t h SPEED
DRIVEN GEARLAYSHAFT REAR ROLLER BEARING
LAYSHAFT-TO-PINION
ADJUSTMENT WASHER 1st SPEED AND)
REVERSE SLIDING GEAR
FIG 6:1Gearbox-differential unit longitudinal section
On the primary shaft extension outside the main central
body is mounted the second-speed driving gear. The
primary shaft is supported at both ends by ballbearings
whilst the clutch shaft rotates in a bronze spigot bush which
is press fitted into the end of the crankshaft. An oil seal is
fitted in the clutch shaft passage seat in the c o n n e c t i o n
support. The layshaft, together with the drive pinion of the
differential unit is supported at the front by a ballbearing
race. The layshaft carries the pinion adjustment shim, the
fourth-speed driven gear and its bushing, the hub and
relevant engagement sleeve for the t h i r d - and fourth-
speed w i t h first-speed and reverse-speed, the third-speed
gear and bushing and, outside the casing the second gear
and bushing, the hub with relevant second-speed engage-
ment sleeve and the speedometer drive gear.
The gears are operated by a gear selection lever mounted
on the tunnel situated between the two front seats. This
operates through a rod actuating the selector and shifting
mechanism which is housed in the gearbox casing cover.
Refer to FIG 6 :3 where it will be seen th a t the positioning
of the striker rods is ensured by a spring-loaded ball-
bearing. The risk of engaging two gears at the same time is
eliminated by three rollers which slide in suitable slots
machined in the rod (see FIG 6 : 4).
The differential unit and the final drive gear train are
housed in the t w o semi-covers which
have previously
been described, the final drive pinion being integral with
the layshaft. The differential casing may be split into t w o
halves. The bevel gear is fitted on one of the halves and is
66
secured by the same screws joining the two halves
together. The differential side gears are internally splined
into which are located the splined axle shaft ends which
are able to slide by means of a specially designed slip joint.
Two specially shaped rubber oil boots are inserted on the
swing axle shafts and fit over the side gear extensions to
ensure that there is no loss of lubricant or the ingress
of dirt.
The transmission and differential unit to suit the station
wagon differs from the sedan in that the transmission to
engine mounting plate and the bellhousing are modified to
suit the engine repositioned on its side.
6 : 2 Removal of gearbox/differential unit:
The complete unit may be removed whilst the engine
remains in situ and to remove this unit proceed as follows:
1 Disconnect the battery positive cable and jack up the
rear of t h e vehicle and place on firmly based stands.
2 Disconnect all control cables and wiring from the
starter motor and the clutch lever. Remove the starter
motor, the clutch lever reaction spring and the clutch
cable support on the gearbox.
3 Remove the three bolts securing each of the driving
shaft flanges to the flexible coupling at the wheel ends
and carefully take out the inner spring.
4 Disconnect the shifter rod from the gearshift lever at the
gearbox extension and also the
speedometer drive
cable. Remove also the flywheel undercover. Place a
suitable support under the engine.

1st A N D 2 n d SPEED
STRIKER R O D LOCK
ROLLER1st A N D 2 n d SPEED
STRIKER R O D 3 r d A N D 4 t h SPEED
STRIKER R O D 3 r d A N D 4 t h SPEED
STRIKER R O D LOCK -
ROLLER REVERSE STRIKER
ROD LOCK ROLLER
REVERSESTRIKER R O D
FIG 6 : 4 Detail of gearbox section through striker rod
lock rollers
2 n d SPEED DRIVENGEAR2 n d SPEED ENGAGEMENT SLIDING SLEEVE 2 n d SPEED FORK 1st A N D 2 n d
SPEED STRIKER R O D REVERSE GEAR3rd AND 4th
SPEED STRIKER R O DREVERSE STRIKER R O D2 n d SPEED DRIVE GEAR SPEED SELECTOR LEVER
FIG 6 : 5 Cross section of gearbox through striker rods
with the indication of the gear selector lever angular
displacement
68
AXLE SHAFT-TO-JOINT SLEEVE
OIL BOOT
RING GEAR
FIG 6:6 Differential unit complete with axle shafts
BEARING CONEADJUSTER LOCK RING BEARING HOUSING DIFFERENTIAL CASE
OIL BOOT RETAINER
AXLE SHAFT
1 Remove the speedometer drive support together with
its gears. Remove the front cover together with its
gasket and the gear selection rod (see FIG 6:2).
2 Remove the lock ring and carefully slide the splined
sleeve from the axle shafts. Remove the t w o roller
bearing housings together with the relevent rubber
boot fastening cover, the rubber boots and the adjuster
ring lock rings.
3 Detach the transmission mounting on engine support
and carefully remove the differential case assembly
complete w i t h the ring gear and axle shafts.
4 Open the fasteners and loosen all the shifter fork lock
bolts.
5 Engage t w o gears at the same time so locking the
input shaft and the mainshaft together. Remove the
cotter pins and the nuts on the front end of the input
shaft and the mainshaft.
6 Remove the retaining cover located on the lefthand
side of the gearbox and carefully take out the shifter
rod positioning balls and springs from their bores.
Remove the upper shifter fork shaft and shifter fork,
the middle shifter fork shaft together with its interlock
pin and also the third and fourth gear shifter fork.
Remove the plain washer and speedometer drive
driving gear from the layshaft.
7 Remove the second gear engagement sliding sleeve
together with the shifter fork, shifter fork shaft, sliding
sleeve hub, second-speed driven gear with relevent
bush and the first gear engagement
fork. Take very
great care not to drop the safety rollers whilst extract-
ing the striker rods.
8 Remove the second-speed driving gear from the input
shaft. Release the reverse shaft retaining screw and
remove the shaft together with the reverse gear cluster.
Remove the layshaft front bearing retaining plate.
9 Push the input shaft forwards until both ballbearing
races are pressed from their seating and the coupling
sleeve located between the input shaft and the clutch
shaft can be reached from above. Carefully remove the
retaining ring and a connection pin at the input shaft
side of the coupling sleeve and carefully withdraw the
clutch shaft and coupling sleeve.
10 Remove the input shaft front bearing race. Tilt the
primary shaft in the casing and remove it from the
gearbox housing. Remove the rear bearing. Carefully

FIG 6:7 Differential components
Key toFig 6:7 1 Axle shafts 2 Sleeve retainment lockrings 3 Slip joint casings 4 Axle shaft-to-wheel shaft
coupling sleeve 5 Differential case cover w i t h bearing inner race 6 Side gears 7 Oil boot retainment cover
8 Side gear thrust ring 9 Idle pinion shaft 10 Idle pinions 11 Oil boots 12 Differential case w i t h bearing inner race
13 Adjuster retainment ring 14 Bearing housings with retaining nuts and outer races 15 Idle pinion shaft retainment cup
1 6 Bevel gear
withdraw the layshaft together w i t h the final drive
pinion and the roller bearing inner race from the rear.
11 From the inside of the gearbox casing carefully slide off
the following parts from the mainshaft, the drive
pinion adjustment shim, the third and fourth driven
speed gears together with their bushes, the t hird- and
fourth-speed hub and sliding sleeve, the first and
reverse driven gear, and carefully drive out the front
bearings and the bevel pinion rear bearing outer race.
1 2 Using a suitable press, drive out the drive pinion roller
bearing inner race from the end of the mainshaft.
Inspection of components:
Before inspecting the various parts removed from the
gearbox casing thoroughly wash all components and
blow dry using a compressed air jet and then proceed as
follows:
1 Thoroughly inspect the gearbox casing to ensure that it
is not cracked and that the bearing seats are neither
F50069 worn or damaged so allowing the bearing outer ring
to rotate during the normal operation.
2 Thoroughly check the ballbearings to ensure that they
are in perfect condition and that both radial ply and
axial play is not excessive. The maximum permissible
bearing play is as follows:
Front bearings of primary shaft layshaft:
(a) Sideways .002 inch
(b) Endwise .017 inch
Primary shaft rear bearing:
(a) Sideways .002 inch
(b) Endwise .016 inch
Hold the bearings firmly by the outer race and gently
rock the inner race backwards and forwards. The sliding
action produced should be free and silent. If any rough-
ness is felt then the bearings must be renewed. Check
the roller bearings by inspecting the condition of the
rollers as well as the outer and inner races. Always fit
new bearings if there is any doubt as to their efficiency.

3 Check the layshaft and the primary shaft between
centres and using a dial gauge ensure that there is no
distortion. The out of true reading for bearing seats
should be less than .0008 inch. Inspect the splines and
ensure that the side and outerfaces are not indented.
Replace if there are signs of wear. Also inspect the
reverse shaft to ensure that it is perfectly smooth and
not showing signs of pitting or partial seizure.
4 Carefully inspect all gear teeth for signs of excessive
wear or damage. The contact faces must be smooth and
show no signs of indentation marks. Also check that
the backlash between the gears, when correctly
mounted on the surface plate is not greater than .0039
inch. The maximum wear limit is .0079 inch. Check that
the quick engagement front teeth of the second-, third-
and fourth-speed gears are not damaged or excessively
worn. Renew if there are signs of gearchange lever
misuse.
5 Inspect the sliding sleeves and the relevent hubs, ensure
that all the working surfaces are perfectly smooth. The
clearance between the mating parts should not be
greater than .0059 inch. Also inspect the meshing teeth
and ensure that they are in good condition.
6 Check that the gear shifting selector forks are not dis-
torted and that the striker rods freely slide in their seats
in the gearbox casing.
7 Carefully inspect that all the oil seals are in perfect con-
dition and if there is any doubt they should be renewed.
8 Inspect the striker rod locking balls and the safety rollers
and ensure that they slide freely in their seatings. Also
check the ball load spring efficiency and if this shows
signs of weakness then it should be renewed. Any
faults with these items will cause difficulty in engaging
gears or autodisengagement during engine acceleration.
6 : 4 Reassembly—gearbox
To reassemble the components to the gearbox ensure
that all components are thoroughly clean and then pro-
ceed as follows:
1 Press t h e pinion rear roller bearing onto the layshaft.
Install the layshaft in the casing, and at the same time
fit the adjustment shim, the fourth-speed driven gear
together w i t h its bush, the sleeve and hub for third and
fourth gear engagement, the first-speed and reverse
driven gear and the third-speed driven gear with its
hub.
2 Install the front layshaft ballbearing securing the
bearing retainment plate w i t h the screws and finally
lock the screws in position.
3 Insert the primary shaft together with the first, third
and fourth driving gear train in the gearbox housing
and slide t h e rear bearing onto the shaft. Push the
input shaft forward to enable the clutch shaft coupling
to be inserted in t h e rear and to be pulled up the
primary shaft by means of the pin. Do not forget the
retaining ring.
4 Slide the primary shaft backwards so pushing the rear
bearing into its bore. Refit the front bearing onto the
primary shaft.
5 On the layshaft insert the second-speed driven shaft
and bush, the second gear sliding dog sleeve and the
hub. Also insert the second-speed striker rod and the
first-speed fork. Do not forget to fit the safety roller
into its seating.
70
6 Slide the second-speed driving gear onto the primary
shaft. Place the engagement fork on the third- and
fourth-speed engagement sliding sleeve, and insert
the striker rod, lock the relevent fork and fit the safety
roller.
7 Insert the third safety roller and install the reverse shaft
and insert the reverse gear cluster onto it and secure
the shaft by tightening its block bolt. Install the reverse
striker rod w i t h its relevent fork.
8 Now refit the speedometer drive worm gear onto the
layshraft. Tighten the nuts on the primary shaft and the
layshaft, not forgetting to interpose the plain washer
between the speedometer driving worm and the nut,
to a torque wrench setting of 1 8.1 Ib ft to 25.3 Ib ft
(primary shaft) and 28.9 to 36.2 Ib ft (layshaft). It is
recommended that the input shaft and layshaft are
locked together by engaging t w o gears at the same
time. Finally, fit the splitpins.
9 Lock the shifter forks onto their shafts by tightening
their respective bolts and bend up the special locking
plates. Install the three positioning balls and relevant
springs into their bores and refit the cover plate.
10 Install the casing cover together with its relevant
gasket. This will enable correct positioning of the shift
shaft lever so that it engages in the outer ends of the
shifter shafts protruding from the gearbox casing.
11 Install the speedometer drive support on the gearbox
casing and refit the upper gearbox cover.
For subsequent differential operations and adjustments
see Sections 6:6.
6:5 Dismantling—differential and final drive
For the removal of the differential and final drive unit
from the gearbox refer to Section 6:3. To dismantle the
differential assembly
proceed as follows:
1 Remove the retaining ring 2 (see FIG 6 : 7) retaining
the splined sleeve 4 and slide the sleeve off the drive
shaft.
2 Remove t h e retaining covers 7 and the oil boots all
together with the bushes and seals, adjuster ring lock
rings 13, adjuster rings housing 14, and bearing
adjuster and roller bearing outer races.
3 Separate the differential housing halves by unscrewing
and removing the six bolts that keep both the halves and
the crownwheel together. It is advisable to mark the
respective components to ensure correct matching
upon reassembly.
4 Remove the differential pinion shaft retainer ring, also
the differential pinions 10 by removing the shaft and
withdrawing the two axle shafts 1.
5 Remove the differential side gears 6 and relevent thrust
rings 8.
6 Using a press remove the differential bearing inner
races from their seats on the carrier halves.
7 Thoroughly clean all parts and dry using a compressed
air jet.
Inspection:
The components of the differential unit must be
thoroughly inspected for correct operation and to deter-
mine the presence of any wear, damage or other irregulari-
ties. To check the items concerned proceed as follows:
1 Check thoroughly the idle pinion carrier shaft for signs

of wear, distorting or unevenness of the surfaces as this
part is very heavily pressed when the vehicle is negotia-
ting a corner. If the clearance to the idle pinions exceeds
.0059 inch the shaft must be renewed.
2 Inspect the ring gear and pinion seat, the side gears.and
the idle pinions for correct meshing. This will be shown
up by white marks on the sides of the gear teeth. Check
that none of the teeth are broken, chipped or exces-
sively worn and if any part is suspect then it must be
renewed not forgetting that the ring gear and pinion
come as a matched pair.
3 Inspect the condition of the ball and roller bearings, the
rollers and balls and working faces must not show signs
of pitting wear or cracking and if any part is suspect then
the race must be renewed.
4 Check that there is not any undue wear on the faces of
the thrust rings. Any slight indentations may be evened
out using a fine oil stone but if the damage is excessive
then new rings or oversize rings must befitted as neces-
sary. Thrust rings are supplied as service spares in the
following thicknesses.
Standard .0394 inch
Oversize .0512-.0591 inch
6:6 Reassembly—differential unit
To reassemble the differential case proceed as follows:
1 Press onto the differential half housing which carries
the ring gear one differential bearing inner race ensuring
that it is pushed fully home onto its seating. Install the
thrust ring and side gear (see FIG 6 : 7).
2 From t h e inside of the case insert the axle shaft com-
plete with pivot and runners that form the slip joint.
Also install the idle pinions and carrier shaft. Position
the ring gear onto the housing half and install the
differential pinion shaft retainer ring.
3 Press the other differential bearing inner race onto its
seating on the left differential housing half and replace
the left axle shaft complete with slip joint.
4 J o i n the t w o case halves together and tighten the
retaining screws and also the retaining screws of the
ring gear to a torque wrench setting of 23.1 Ib ft. Secure
all screws by bending up the lockplates.
5 Press t h e differential bearing outer races into their
seatings in the bearing housings and also f i t the o i l seals.
Also install the bearing housings over the driving shafts
together with the adjuster rings.
6 Install the differential unit assembly into the final drive
housing front half and bolt the rear
half onto it. Tighten
the six mounting nuts to a torque wrench setting of
27.5 Ib ft. Finally place the bearing housings in their
seats and tighten the mounting nuts to a torque wrench
setting of 13 lb ft.
It should be noted that after the gearbox has been over-
hauled the complete differential unit should only be in-
stalled after the drive pinion depth adjustments has been
carried out.
6 : 7 Final drive gear set adjustment
The installation and adjustment of the final drive gear
set requires special care otherwise the unit may have to be
dismantled again for further adjustment. So as to establish
the correct mesh of the t w o gears, their relative position is
accurately set during initial assembly at the factory.
F50071 Refer to FIG 6 :8 where it will be seen that t w o numbers
are stamped on the pinion shaft near to the threaded end,
the upper number is the matching number which should
also appear on the crownwheel. The lower number indi-
cates the positive or negative deviation from the theoretical
distance between the centre line of the ring gear and the
pinion face. It is this number which must be taken into
account when calculating the adjusting shim thickness
which has to be fitted between the rear roller bearing and
the fourth-speed gear on the layshaft.
The formula from which the adjusting shim thickness
can be calculated is as follows:
S=A—(B + C)
Where S=shim thickness.
A= distance between the front bearing inner
race and the centre line of the ring gear.
B = distance of the drive pinion face to the ring
gear centre line.
C = t h e total of the widths of the third-speed
gear bush, third- and fourth-speed hub,
fourth-speed gear bush and rear roller
bearing inner race fitted onto the mainshaft
It should be noted that 'A' is the total of half the diameter
of the differential bearing housing seat which is in actual
fact 41.00 mm, and the distance measured between the
front bearing inner race and the differential bearing housing
seat. The last
dimension will have a minimum manufactu-
ring limit of 150.54 mm. Any deviation from this value
must be determined and considered when determining
the total shim thickness 'S'.
A= 150.54 + 41.00 + a (deviation)
To determine deviation 'a' Fiat tool A.62036 should be
assembled to the gearbox casing as shown in FIG 6 : 9
and to take the reading proceed as follows:
1 Assemble the front ballbearing and its retainer into the
gearbox housing and tighten the retainer bolts.
2 Hold the gearbox housing in the vertical position with
the differential side upwards and insert Fiat tool
A.62036 carefully from above into the bearing bore and
lock it firmly by tightening the knurled nut.
3 Using Fiat dial gauge C.689 which has been previously
zeroed on a surface plate should next be mounted
onto the t o p of Fiat tool A.62036 with its pointer resting
on the lowest position of the differential bearing hous-
ing bore as shown in FIG 6:10. To obtain the lowest
point move the pointer to both sides of the bottom dead
centre position so as to obtain the maximum reading.
The distance ' B ' in the formula for calculating the shim
thickness is designed to have a lower manufacturing limit
of 75 mm. Any deviation ' b ' is stamped on the drive pinion.
Therefore to calculate the value of ' B '
B = 7 5 + b (deviation)
The distance 'C' in the formula for calculating the shim
thickness is designed to have a lower manufacturing limit
FIG 6 : 8 Layshaft w i t h final drive pinion. The arrow
points to the number (14) for correct mating with ring
gear and to the centesimal figure (—10) for accurate
mating position of pinion and gear