1972 FIAT 500 front

FIG 1 :48 Power plant front support cross-section
FIG 1 :49 Checking the generator and blower drive
belt tension
1 :19 Power plant mountings
The combined power and transmission unit is elastic-
ally mounted on two supports.
The front of the unit rests on a crossmember which is
secured under the car floor through two rubber block
mountings that are bolted to the gearbox casing as
shown in FIG 1 :48. The position of the rubber blocks
on the crossmember is adjustable so that the assembly
can be correctly aligned.
W i t h t h e rear of the unit the engine crankcase is sprung
to the b o d y rear crossmember through an articulated
swinging arm that compresses a coil spring as shown in
FIGS 1 :47 and 1 :49. A rubber bump pad is mounted
inside the spring to give a progressive action.
Whenever the power and transmission unit is being
serviced the condition of the mountings should be
checked and any worn or damaged parts renewed.
1 :20 Adjustment of generator and fan drive belt
The centrifugal oil filter cover/pulley on the crankshaft
transmits the drive through a V-belt to the generator and
centrifugal fan pulley.
32
(b) Engine stalls
1 Check 1, 2, 3, 4, 10, 1 1 , 12, 13, 14 and 15 in (a)
2 Sparking plugs defective or gaps incorrect
3 Retarded ignition 1 Defective coil
2 Faulty distributor capacitor (condenser)
3 Dirty, pitted or incorrectly set contact breaker points
4 Ignition wires loose or insulation faulty
5 Water on sparking plug leads
6 Corrosion of battery terminals or battery discharged
7 Faulty or jammed starter
8 Sparking plug leads wrongly connected
9 Vapour lock in fuel pipes
10 Defective fuel pump
11 Overchoking
12 Underchoking
13 Blocked petrol filter or carburetter jets
14 Leaking valves
15 Sticking valves
16 Valve timing incorrect
17 Ignition timing incorrect
(a) Engine will not start 1 :22 Fault diagnosis
Since its introduction the Fiat new 5 0 0 model has
been continually developed. The main modifications that
have been made are as follows:
1 Heating system safety device
2 Recirculation device for the blow-by gases
3 Cylinder head modified to incorporate item 1
4 Double valve springs fitted
5 Cylinder barrels modified to incorporate item 1
6 Flywheel modified to incorporate new type diaphragm
spring clutch mounting
7 Larger air cleaner container.
Details of these modifications are to be found in the
relevant sections if they necessitate a change in service
overhaul procedure. Other information is to be found in
Technical Data.
1 :21 Modifications
When the V-belt has been correctly adjusted the belt
should sag 13/32 inch under a hand pressure of about 22 lb
as shown in FIG 1 : 4 9.
Should the belt be too slack the generator and
centrifugal fan will not operate at the correct speed
causing overheating and a discharged battery. Also the
belt will slip causing rapid wear of the belt. Conversely
if the belt is too tight excessive loading will be placed
on the generator bearings causing excessive bearing
wear and noisy operation.
To adjust the belt tension proceed as follows:
1 Remove the three nuts ' B ' (see FIG 1 :49) on the
generator pulley and this will split the pulley into two
parts between which are spacer rings.
2 The tension of the belt is increased or decreased by
either reducing or increasing the number of spacers.
3 Place the spacer rings removed from between the
pulley halves on the pulley outer face so that the rings
may be re-inserted when fitting a new belt.
4 Tighten the three nuts to a torque wrench setting of
14.5
lb ft.
Key to Fig 1 :49 A Normal give-in: about 13/32 inch under
a 22 Ib pressure B Nuts securing the pulley halves with
spacer rings

CHAPTER 2
THE FUEL SYSTEM
2:1 Description
2 : 2 Fuel pump operating principles
2 : 3 Routine maintenance
2 : 4 Pump removal, dismantling and examination
2 : 5 Reassembly, installation and adjustment
2 : 6 Carburetter operation and adjustment,
Weber 26.1MB2 : 7 Modifications
2 : 8 Carburetter operation and adjustment,
Weber 26.OC
2 :9 Air cleaner
2 : 1 0 B l o w - b y gases recirculation device
2:11 Fuel tank
2:12 Fault diagnosis
2:1 Description
All the new 500 models use a mechanical diaphragm
fuel feed pump as shown in FIG 2 : 1. Four types of
carburetter are fitted depending on the model to which
the engine is installed. Each carburetter operation and
adjustment is fully described, together with details of the
recirculation device for blow-by gases and o i l vapours.
2 : 2 Fuel pump operating principles
Refer to FIG 2 : 2. An eccentric on the rotating camshaft
actuates the operating rocker 21 via a pushrod 25 which
depresses the diaphragm 14 and so creates a depression
in the pumping chamber located in upper body 5. Under
atmospheric pressure, petrol passes through the pipeline
connection and inlet valve into the pumping chamber.
The return spring 15 then raises the diaphragm, expelling
the petrol through the outlet valve and pipeline to the
carburetter float chamber.
When the float chamber is full, the pressure in the pipe-
line and pumping chamber holds the diaphragm depressed
against the tension of the return spring.2 : 3 Routine maintenance
A poor delivery of fuel to the carburetter may be due to
a fault in the fuel pump or related lines. Periodically the
pump body screws 19 (see FIG 2 : 2) and upper cover
screw 1 should be checked for tightness. The fuel pump
lines should be disconnected and checked for freedom of
restriction, chafing and loose connections. The fuel pump
filter should be removed and cleaned periodically.
2:4 Pump removal, dismantling and examination
The pump is located on the carburetter side of the
engine crankcase (sedan) or under the generator at the
front of the crankcase (station wagon).
Removal:
1 Disconnect the fuel pipe from the tank to stop petrol
syphoning out of the tank and then release the fuel
inlet and outlet pipes from the pump body.
2 Remove the t w o nuts and washers holding pump to
crankcase.
3 Carefully lift away the pump, gaskets and insulating pad
from the crankcase (see FIG 2 : 3).
F50035

Air cleaner—station wagon:
A pleated paper air cleaner element is housed in a
special air intake chamber connected to the front of the
engine air cooling cowling (see FIG 4 : 2) . This chamber
will be seen located towards the rear of t h e power unit
compartment. Remove the retaining wing nut, lift off the
lid and the element can be withdrawn by lifting upwards.
2:10 Blow-by-gases recirculation device
Engine 110 F.000
All the oil vapours and blow-by-gases that are formed
in the engine crankcase are drawn to the cylinder head
cover recess 1 (see FIG 2:18). From here they travel into
the pipe 5 via a breather valve 2 which is firmly attached to
the oil filler cap 3 and the strainer 4 located in the filler
neck. The oil vapours and gases are then d r a w n back into
the duct 9 from the pipe 5 which connects the air cleaner
6 to the carburetter 7. This ensures a complete closed cir-
cuit circulation.
Engine 120.000:
From engine No. 288156 the oil vapours and blow-by-
gases instead of being exhausted to the atmosphere are
conveyed to the air cleaner and from here they are drawn
back into the combustion chambers. To ensure that an
excessive of oil vapour does not pass along the piping
with the blow-by-gases a diaphragm is fitted in the duct
in front of the breather valve 2 (see FIG 2 :18), the dia-
phragm comprising a filter gauze 11 and moveable parti-
tion 10.
It should be noted that the oil vapour strainer 4 (see
FIG 2:18) and the flame trap 8 can easily be removed
from their seating for cleaning or renewal.
2 : 1 1 Fuel tank
The fuel tank is located in the front compartment as
shown in FIG 2:19, it comprises a filler union fitted with a
cap, a fuel reserve supply indicator sender unit and a con-
nection incorporating a filter for the main fuel supply pipes.
To remove the tank proceed as follows:
1 Remove the contents of the front compartment includ-
ing the spare wheel and tool bag.
2 Disconnect the main fuel line at the sender unit and also
disconnect the cable to the fuel reserve supply indicator.
3 Remove the four screws together w i t h the clips that fix
the tank to the body and carefully lift away the fuel tank.
4 Carefully drain the contents of the tank into a clean dry
container of a suitable capacity.
Fuel tank—sedan (110 F.) and station wagon (120):
The fuel tank is arranged in the front compartment as
shown in FIG 2 :20. To remove the fuel tank proceed as
follows:
1 Remove both screws which secure the front ends of the
clamping bands to the dash panel. The screws are
shown by arrows in FIG 2 :20.
Petrol tank cleaning:
The tank must be thoroughly checked for leaks espe-
cially at the joint seams. Should a leak be found it is
F50045
advisable for a garage to attend to this as it is very dange-
rous to apply heat to a petrol tank without first taking strict
precautions and a garage will be in a better position to do
this. To clean the tank interior, remove the drain plug and
spray in a jet of air or petrol so that all sediment and dirt
deposits can be loosened. Then vigorously shake the tank.
Flush the tank w i t h petrol and blow the tank dry. Repeat
this procedure until the tank is clean. Refit the drain plug.
Whilst the petrol tank is away from the car it is advisable
to disconnect the fuel feed pipes at the pump and the
carburetter and ensure that these are clear by using an air
jet to one end of the pipe.
Key t o Fig 2 :20
Note Arrows point to fuel tank clamping band screws vent valve
indicator tank unit1 Fuel tank2 Filler cap with
3 Fuel suction pipe and reserve supply
4 Tank clamping bands
FIG 2:20 Location of the fuel tank in front compart-
ment, 500F, L FIG 2:19 Fuel tank in front compartment. The fuel
reserve supply indicator (red light) glows when fuel
amount in tank is less than .8 to 1.1 Imp galls, or 5 litre FUEL TANK
FUEL LINE TO PUMP
FUEL GAUGE CABLE

CHAPTER 6
GEARBOX AND DIFFERENTIAL UNIT
6:1
6:2
6:3
6:4
6:5
6:6Description
Removal of gearbox/differential unit
Dismantling — gearbox
Reassembly — gearbox
Dismantling — differential and final drive
Reassembly— differential and final drive6:7
6:8
6:9
6:10
6:11
6:12Final drive gear set adjustment
Replacement of gearbox/differential unit
Swing axle shafts and slip joints
Gear shift control mechanism
Modifications
Fault diagnosis
6 :1 Description
The gearbox and differential unit are housed in an
aluminium alloy casing made up of t w o parts which split
at the differential centre line. The output drive is trans-
mitted by means of t w o half axle drive shafts coupled
through wheel shafts and slip joints to the rear wheels (see
FIG 6 : 1)
The gearbox provides four forward-speeds and a reverse,
the fourth-speed being considered as an overdrive. All
gears except first and reverse gears, which are straight
toothed sliding gears, are in constant mesh and have heli-
cal teeth. No synchromesh is provided, gear engagement
being completed by sliding shifter sleeves of the dog
clutch type. The first-speed gear slides on the outside of
the third and fourth shifter sleeve, whilst the reverse gear
train moves on a fixed shaft. The clutch shaft is integral
with the third, top and combined and first and second gear
pinions, whilst the second gear pinion is splined at the
front end. An internal splined
coupling sleeve joins the
clutch shaft and the input shaft and transmits the power
from the engine to the gearbox. The mainshaft and
differential drive pinion are combined together and besides
carrying the constant mesh gears and the sliding first gear
pinion, it also has attached the sliding sleeves and hubs.
F50065 The speedometer drive pinion is located at the front end.
The gearbox/differential casing is attached to the engine
by six studs which locate in the crankcase. The front of the
unit rests upon the rubber mounted support which is
secured to the body floor.
The complete unit comprises three detachable parts
made up as follows:
1 The support for the connection of the gearbox to the
engine which also acts as part of the differential front
end and clutch/flywheel housing at rear.
2 A central body which is divided into two compartments.
The front compartment contains first, third, fourth and
reverse gears w i t h the primary shaft, layshaft and reverse
shaft as well as the necessary gear selection striker rods
and forks. The rear of this compartment also forms a half
cover for the differential unit.
3 The gearbox casing cover, which contains the second-
speed gears together with the relative fork, gear
selection rod and speedometer drive gears.
The central part of the casing is provided with a top
inspection cover. The primary shaft is coupled to the clutch
shaft through an internally splined sleeve and t w o pins
which are retained by rings. The primary shaft together
with the first, third and fourth driving gears form a cluster.

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.

FIG 6 :2 Gearbox gears, forks and striker rods
KeytoFig6:2 1 Rear roller bearing 2 Layshaft with bevel pinion 3 Front ballbearing 4 Front bearing plate
5 Bushing 6 Fourth-speed driven gear 7 Third- and fourth-speed sliding sleeve 8 First and reverse sliding gear
9 Sliding sleeve hub 10 Third-speed driven gear 11 Bushing 12 Bushing 13 Second-speed driven gear
14 Second-speed sliding sleeve 15 Second-speed sliding sleeve hub 16 Speedo drive gear 17 Reverse sliding gear
18 Reverse sliding gear shaft 19 Clutch shaft 20 Clutch shaft-to-primary shaft sleeve 21 Primary shaft rear ballbearing
22 Primary shaft with first and reverse, third and fourth gear train 23 Primary shaft front ballbearing 24 Second-speed drive gear
25 First gear fork 26 First and second gear striker rod with second gear fork 27 Reverse gear fork 28 Reverse gear striker rod
29 Third and fourth gear fork 30 Third and fourth striker rod 31 Gear selector and engagement lever
SPRING
GUIDE BUSHES
REVERSESTRIKER R O D
BALL SPRINGS
POSITIONING BALLS STRIKER R O D
BALL SPRING
COVER PLATE
1st A N D 2 n d SPEED
STRIKER R O D3 r d A N D 4 t h SPEED
STRIKER R O D
FIG 6 : 3 Detail of gearbox section through striker rod
positioning ball springs
F50067 5 Using a garage type hydraulic jack fitted with Fiat
support Arr.2076 carefully placed under the gearbox-
differential unit take the weight of the unit from the
front mounting. Carefully remove the nuts securing the
transmission unit to the engine and also the nuts that
secure the transmission front support to the body
brackets.
6 Carefully draw the transmission forwards away from
the engine taking very great care that no weight is
allowed to act on the clutch shaft until the end of the
clutch shaft is clear of the flywheel and clutch cover
assembly. Carefully lower the transmission to the floor.
7 Remove the front support together with its rubbers,
drain the oil from the transmission unit and thoroughly
wash the outside to remove all traces of dirt and grease
and dry using a compressed air jet. The transmission is
now ready for dismantling.
6:3 Dismantling— gearbox
Before dismantling the gearbox ensure that the exterior
is thoroughly clean and then proceed as follows:

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.