1970 FIAT 500 differential

FIG 6:9 Graphic demonstration of values A and a
'A' Distance between pinion front bearing inner shoulder and
the axis passing through the differential bearing housing
centre'a' Difference between the minimum value called out on drawing
(5.9268inches — 150.54mm) and actual machining value
of the distance between pinion front bearing inner shoulder
and differential bearing housings
DIAL GAUGE C.689TOOL A.62036
FIG 6:10 Reading value a on gauge C.689 to determine
drive pinion shim thickness
72The procedure for adjustment of the final drive gear
set is exactly the same as for the new 500 model except of 115.64 mm. Fiat tool A.62037 as shown in FIG 6:12
used in conjunction with the dial gauge can now be used
to measure the deviation 'c' from the lower manufacturing
limit as follows:
1 Place the dial gauge on a stand on the surface plate and
place Fiat tool A.62037 on the plate as shown in the
FIG 6 : 1 1 .
2 Carefully slide onto the Fiat tool the following items,
third-speed driven bush, third- and fourth-speed gear
engagement sleeve, hub, fourth-speed driven gear bush
and drive pinion roller bearing inner race. Set the dial
gauge to zero using Fiat tool A.62037 as the datum and
then rest the dial gauge plunger on the roller bearing
inner race and take a reading at the dial as shown in
FIG 6 :11. This reading will represent 'c' which can now
be used in the formula.
C=115.64+c (deviation)
Once the values of A', ' B ' and 'C have been found as
detailed above we can now insert the values into the basic
formula S = A—(B + C) which will now give us:
S = 1 50.54 + 41.00+ a — (75+ b +115.64 + c )
which can be simplified by using algebra to give us the
following formula:
S = 0.90 + a — ( b + c)
Shims are supplied in the following thicknesses,
.0039 inch and .0059 inch. One or more shims should be
used to make up the
required shim thickness.
Adjusting final drive gear set (500D, and 500F
sedan and early station wagon):
FIG 6:11 Setting dial indicator to zero on tool A.62037
TOOL
A.62037

FIG 6:12 Graphic demonstration of C and c
Key to Fig 6:12 1 Bevel pinion rear roller bearing inner
race 2 Bush, fourth-speed driven gear 3 Hub,
third- and fourth-speed engagement sleeve 4 Bush,
third-speed driven gear
'C Total height of items 1, 2, 3 and 4 which must be mounted
on final drive pinion
'c' Difference between actual height C and the minimum
drawing call-out 4.5527 inch represented by tool A.62037
that the new Fiat tools are used to determine shim thick-
ness as detailed below:
S = 0.90 + a — (b + c)
Where S = shim thickness
0.90 = standard coefficient
a = value of reading on the dial indicator
A.95690 applied to fixture A.70036 as
shown in FIG 6:13.
b = value stamped on pinion stem as shown in
FIG 6:8.
c= value read o n the dial indicator corres-
ponding to the difference between height
of Tool A.70037 as shown in FIG 6:14,
and the sum of the thicknesses of the items
to be installed in pinion and included
between front bearing inner shoulder and
rear bearing outer shoulder.
Ring gear clearance and differential bearing pre-
load :
To enable the correct ring gear tooth clearance to be
ascertained use Fiat tool A.62039 together with a dial
gauge. The support for dial gauge should be fixed into
the t w o lower bolt holes of the flywheel housing and the
pointer of the dial gauge adjusted so that it is located
through the clutch shaft hole in the final drive housing
so resting on a ring gear tooth (see FIG 6:15). Then
proceed as follows:
1 During reassembly the differential bearing nuts should
not have been screwed fully home to the differential
F50073
bearing outer races w h e n installing into the f i n a l drive
unit. These should now be carefully screwed in until
they are in gentle contact with the bearing races.
2 Slide Fiat tool A.62040 over one of the drive shafts
and using Fiat tool A.62041 lock the drive shaft to
the differential housing thus preventing the drive
pinion from rotating.
3 Gently turn the drive shaft which should now be
locked to the ring gear and note the movement of the
dial gauge indicator. This will show the tooth clear-
ance. When the clearance is correctly adjusted the
FIG 6:14 Reading value c on dial indicator Key to Fig 6:13 1 Dummy pinion, tool A.70036
2 Support with dial gauge, tool A.95690 FIG 6:13 Diagram showing the position of tools for
determining the value of a

TOOL A 62039
TOOLA. 62040 PIN WRENCH A. 52022
FIG 6:15 Adjusting ring gear-to-pinion backlash and
differential bearing play, using special wrench A.52022
reading on the dial gauge should be between .0031 to
.0047 inch. The actual clearance is adjusted by
screwing in one adjusting nut and screwing out the
other by the equivalent amount using Fiat spanner
A.52022 as shown in FIG 6:15.
4 Remove Fiat tool A.62041 and using Fiat support
A.62040 mount the special dynamometer A.95697 and
adaptor on the axle shaft. Rotate the axle shaft several
turns so seating the bearings and then check using
the dynamometer the rotation torque.
5 If necessary tighten or slacken the adjusters until the
specified torque of 1.01 ± .07 lb ft is obtained. This
operation must be very carefully carried out because if
one adjuster is set differently with respect to the other,
a variation in ring gear to pinion backlash may take
place, resulting in a variation of rotation torque. After
any adjustments always recheck on the ring gear to
pinion backlash and if necessary readjust and then
repeat the rotation torque check.
6 Finally check the tooth contact between the pinion
and ring gear as detailed in the following instructions:
Check and adjustment of tooth contact between
pinion and ring gear:
1 Carefully apply to the ring gear teeth a thin layer of
engineers' blue and gently rotate the differential whilst
holding the axle shaft firmly but allowing them to slip
slightly so as to have the unit working under load
conditions.
2 A contact impression will be left on the ring gear teeth
and the contact will be correct when the drive pinion
tooth contact pattern is evenly distributed on the ring
gear teeth as shown in FIG 6:16. Should the tooth
contact be incorrect the following observations should
be noted.
Excessive contact on tooth flank. Too deep
meshing — move pinion out from ring gear by reducing
thickness of shim.
Excessive contact on tooth heel. Too slight
meshing—move pinion in towards ring gear by
increasing thickness of shim.
74
6 : 8 Replacement of gearbox—differential unit
Installation is the reverse procedure to removal of the
unit from the vehicle as described in Section 6:2.
However, the following points should be noted:
1 Ensure that the clutch driven disc hub is correctly
aligned with the clutch shaft pilot bush.
2 The complete transmission unit should be carefully
pushed towards the engine and the clutch shaft
inserted into the driven disc hub splines and finally
home into the pilot bush. Extreme care must be taken
to ensure that no weight is placed on the clutch shaft
otherwise distortion may take place.
3 Carefully connect the gearbox rear housing to the
engine crankcase by using the studs, t w o of which
have special location dowels fitted. Screw home
finger tight the gearbox/differential to body to front
support mounting screws inserting the fibre washers.
Lower the hydraulic garage jack and pull it away from
underneath the vehicle. Screw in the four lower
mounting nuts and tighten to a torque wrench setting
of between 18.1 to 21.7 Ib f t.Finally tighten the front
support screws.
4 Reconnect the gear shift control rod and the speedo-
meter drive cable. Insert the springs between the axle
shafts and wheel drive shaft and tighten the
three
mounting screws of each splined sleeve on the
flexible joint to a torque wrench setting of 20.3 Ib ft.
5 Refit the flywheel housing cover. Replace the starter
motor together with its relevant cover and tighten the
two mounting nuts to a torque wrench setting of
18.1 to 21.7 Ib ft. Reconnect the starter control rod,
the t w o starter cables, the clutch control tie rod and
hook up the return spring and secure the clutch
control cable retainer bracket to the gearbox casings.
Reconnect the cable to the battery positive terminal
post
6 Lower the vehicle to the floor gently and then give a
thorough road testing.
6 :9 Swing axle shafts and slip joints
Description:
The t w o axle shafts are connected to the differential
unit through specially designed slip joints which allow
the shafts to swing and slide in the splined housing in
the differential side gear. At the other end, the axle shafts
are connected to the wheel drive shaft flexible joints
using a sliding sleeve. Excessive contact on tooth face. Too slight
meshing—move pinion in towards ring gear by in-
creasing thickness of shim.
Excessive contact of tooth toe. Too deep meshing
—move pinion out from ring gear by reducing thickness
of shim.
With all the above detailed cases, to adjust the pinion
by replacing the shim, the differential unit and drive
pinion shaft must be dismantled. This means that when
the unit is reassembled after the necessary adjustments
have been made, the backlash and bearing rotation
torque must be repeated.

LEVER SUPPORT SCREWS BOOT MOUNTING SCREWSGEARSHIFT LEVER BOOT
GEARSHIFT LEVER
FIG 6:17 Location of gearshift lever on control passage
tunnel
Repair and inspection :
Whilst servicing the assembly thoroughly check the
condition of the slip joints sliding surfaces and the
housing in the differential side gears. If, due to wear, the
clearance is greater than .008 inch the slip joints should
be renewed or in extreme cases the differential side gears
as well.
Also check the clearance between the slip joint pivots
and runners and if it is found to be excessive the axle
shafts must be renewed as well as the runners as the
joint pivot is not supplied as a service spare part. The axle
shaft to sliding sleeve spline clearance should not exceed
.006 inch.
Check that the sliding sleeve snap ring is a snug fit in
its seating groove on the shaft.
Whenever the vehicle is being serviced the condition
of the boots, bushings and oil seals should be checked
and any damaged parts renewed.
6:10 Gear shift control mechanism
Should difficulty be experienced in obtaining correct
gear selection then the gear shift control mechanism
should be adjusted as follows:
1 Remove the screws fixing the cover to the tunnel and
raise t h e cover to t h e t o p of the gear shift lever stem.
2 Slacken the lever support mounting screws and push
the support forward if first- and third-speed engage-
ment is incorrect or backwards if second-, fourth- and
reverse-speed engagement are incorrect. Finally tighten
the mounting screws. Refit the gear shift lever boot.
Removal:
To remove the gear shift control mechanism from the
car proceed as follows:
1 Unscrew the gear shift control lever knob and the boot
fixing screws and slide the boot from the gear shift
lever.
76Key to Fig 6:18 1 Hand lever 2 Inner lever
3 Lever return spring 4 Hand lever spring 5 Ball seat
6 Inner lever-to-rod mounting screw 7 Gearshift control rod FIG 6:18 Gearshift control mechanism
6:11 Modifications
Various design modifications are incorporated on the
500 sedan (110F) and the late version of the 500 station
wagon. These are shown in FIGS 6:19 and 6:20, The gear shift handlever is removed by releasing the
lever to support mounting self-locking nut.
Check that the lever ball and socket are in good
condition and not badly pitted or worn. The inner lever
return spring and the hand lever spring should be checked
for weakness which, if apparent, should be renewed.
Reassembly is the reverse procedure to dismantling. Dismantling and inspection: 2 Remove the screws fixing the assembly to the tunnel.
Remove the tunnel front cover.
3 Disconnect the gear shift control rod at the gear
engagement control lever and pull out the assembly
from the front end.

FIG 6:19 Modified items in transmission-differential assembly
Key to Fig 6:19 1 Reverse shifter shaft 2 Third and fourth shifter shaft 3 First and second shifter shaft
4 Countershaft pinion (and ring gear) 5 - 7 Transmission-differential case 6 Housing 8 Clutch shaft
FIG 6:20 End sectional view of transmission — differential assembly
The items having undergone design modifications, besides and final drive gears 2 Seal 3 Bushing 4 Oil
those shown in Fig 6 :19 are the following: 1 Differential case boot 5 Axle shaft 6 Joint casing
77F500