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Fig. 54
Preload Adjusting Points
either direction at the locks, a short
interval of slack will be observed
where the worm follower and rack
and sector teeth are exhibiting back-
lash.
Note the maximum torque read-
ing in this slack interval. This should
be approximately
~
to 1 inch pound.
2. Worm
Bearing
Preload
Whilst oscillating the input shaft in
this same slack interval, the bearing
adjusting screw should be tightened
until an
increase
in torque is noticed.
The adjusting screw should be locked
to achieve an
increase
over the input
seal friction of 1 to 2 inch pounds
(for new parts 2 to 3 inch pounds).
Additionally, note the actual torque
reading.
3. Gar Drag
input shaft over a greater angle (be-
~
to
*
turn off centre. Oscillate the
input shaft over a greater angle be-
tween the limits
~
to
*
turn off
centre) and observe the maximum
torque reading. It will be noticed
that this reading is slightly higher
than the previous reading by about
~inch
pound (for a new gear 1 to 1
~
inch pounds). This additional torque
is due to frictional drag between
worm and follower, rack and sector
teeth, the piston seal in the housing
bore and the sector shaft seal. Be
careful not to measure this torque
any closer to centre than a
~
turn,
otherwise the results will be influen-
PART
3-3-
POWER STEERING
3-37
Fig. 55
Checking Preloads - Typical
ced
~y
the changing ratio of the
worm. It may also be observed that a
slightly higher reading is produced
when turning the gear left. This is
due to the
10°
inclination of the
piston when the gear is set horizontal.
The piston is pushed up the inclina-
tion on a left turn and down the
inclination
on
a right turn.
4.
Worm Follower Preload
Bring the gear to the on centre
position which will bring the worm
follower adjusting screw accessible
through the hole in the top cover.
Turn the adjusting screw a % turn at
a time until an increase in torque
reading is noted when oscillating the
input shaft
5°
either side of centre.
Ensure that the Allen key is with-
drawn from the adjusting screw
during oscillation of the input shaft,
otherwise damage may result to the
threads for the top cover !lug. The
preload should be adjuste until an
increase of
3
to
4
inch pounds is
achieved over the last actual reading.
(For new components 6 to 7 inch
pounds.) Note the actual reading.
Replace the plug in the top cover and
tighten to 7-9 foot pound torque.
5.
Rack and Sector Tooth Preload
With the gear on centre oscillate
the input shaft 5 degrees either side of
centre and sj.owly turn the rack
adjusting screw clockwise until an
increase in preload is observed. When
an increase of 3 to 4 inch pounds
(for new components
6
to
1
inch
pounds) is observed, hold the rack
adjusting screw with an Allen key
and tighten the rack adjusting screw
locknut. This adjustment is very sen-
"
sitive and some trial and error will be
required to achieve the correct pre-
load after the locknut is tightened.
The locknut should be tightened to
30 foot pounds torque.
6. Final Check
As a fmal check, turn the box from
lock to lock to ensure that there are
no 'hang-ups'. Sensible preload should
occur over a broad angle of approxi-
mately
%
turn either side of centre,
with the highest preload occurring
through centre.
Refitment of Gear to Vehicle
The gear must always be refitted
to the vehicle
so
that the gear is 'on
centre' when the vehicle is tracking
straight ahead. This is important as it
ensures that the
peak
in the ratio
curve of the gear occurs when driving
straight ahead and the ratio change is
then symmetrical in right and left
turns.
Hence first 'centre' the steering
wheel then make all tracking correc-
tions by adjustment of the steering
side rods only.
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