Preparing for shimming
Fit the tapered roller bearing cone (7) (if removed) against
the pinion shoulder using a press and a suitable fixture. Fit:
- the tapered roller bearing cup (10) against the shoulder
of the hand brake unit (15);
- the tapered roller bearing cup (2) against the cover
plate shoulder (13).
Firmly tighten tool ref. 3378464M1 in a vice. The pinion's tapered roller bearings are shimmed outside of the centre housing
using the service tool
3378464M1. The hand brake unit
must be bare (free of discs and intermediate plates).
Fit the unit (15) and the cover plate (13) to the tool
using the screws (8) tightened step-by-step in diametric
opposition to a torque of 100 - 130 Nm. Determine a shim (3) thickness in order to achieve a
temporary clearance of approximately 0.15 to 0.20 mm, as a preliminary step to shimming with preload
P1. Insert the pinion fitted with the tapered roller bearing
cone (7) into the hand brake unit (15). Slide the following onto the pinion:
- the thrust washer (4) against shoulder E;
- the shim(s) (3) determined.
Fit the tapered roller bearing cone (1). Using wrench ref. 3378118M1 and socket ref. 3378119M1,
tighten the nut (18) temporarily to a torque of 200-250 Nm.
Shimming
Pinion/hand brake unit assembly adjustments must be made
in the following order:
Adjusting the preload on tapered roller bearings
(1) (2) and (7) (10). This adjustment is to be carried out in two phases:
- Phase 1: This phase consists of using a dial gauge
and following the conventional method by applying a firm axial push and pull
force on the pinion in order to carry out shimming P1.
- Phase 2: This phase is mandatory. It is intended to
fine-tune shimming P1 by measuring and adjusting (if necessary) the rotational
torque of the tapered roller bearings (1) (2) and (7) (10) using a dial-type
torque wrench.
Adjusting the position of the pinion/hand brake
unit. Assembly Adjusting the preload on tapered roller bearings (1) (2) and (7) (10).
Phase 1
Place a dial gauge on the base of the tool. Position its
feeler pin on the flat end of the pinion.
Pull the pinion firmly by its front section while turning
it alternately to the right and left in order to correctly position the tapered roller bearing cone (7)
in the cup (10). Set the dial gauge to zero.
Repeat step, pushing firmly in order to correctly position
the tapered roller bearing cone (1) in the cup (2). Depending on the clearance reading on the dial gauge,
select another shim (3) thickness to obtain a preload (detail A): P1 = 0.01 to 0.05 mm. As far as possible, shim to the maximum
tolerance.
Loosen the nut (18). Remove the tapered roller bearing
cone (1).
Slide the shim(s) selected at step between the thrust
washer (4) and the tapered roller bearing cone (1) (detail B). Using wrench ref. 3378118M1 and socket ref. 3378119M1,
gradually tighten the nut (18) to 200-250 Nm.
Phase 2
Keep the pinion/hand brake unit assembly fixed to tool
ref. 3378464M1. Now adjust or check the rotational torque of the pinion's
tapered roller bearings. Using a dial-type torque wrench and socket ref.
3378119M1, and one or two suitable adaptor(s) (if necessary), turn the pinion gently and smoothly
a few turns without stopping and without changing speed. Read off the rotational
torque on the torque wrench dial:
it should be between 1 and 5 Nm. The adjustment principle consists of adding or removing one or more shim(s) (3)
to obtain the rotational torque
specified above. If possible,
adjust it to the maximum tolerance.
If it is necessary to unscrew the nut (18) to add or remove
the shim(s) (3), retighten this nut to 200-250 Nm in preparation for measuring
the distance concerning the position of the pinion/hand brake unit assembly in the
centre housing. Adjusting the position of the pinion/hand brake unit assembly. After adjusting the rotational torque of the
pinion's tapered roller bearings,
adjust the position of the
pinion/hand brake unit assembly. To
adjust the position of the pinion/hand brake unit assembly, keep the assembly fixed to the service tool.
The shim (12) thickness required to position the pinion/hand
brake unit assembly are calculated using the formula below: E = Y2-0.08 + (Y1-0.01)-Z where:
E = Shim thickness to be fitted
Y1 = Distance measured between the pinion end and the
mating face of the hand brake unit
Y2 = Theoretical nominal value of the pinion: 139 mm
Z = Theoretical nominal value between the mating face
of the hand brake unit on the centre housing and the centre line of the differential
ring gear axis (20): 239.35 mm (-0.01 mm) = Anticipated variation in the taper distance
following deformation of the hand brake unit during tightening on the centre housing. (-0.08 mm) = Anticipated variation in the taper distance
under load in forward travel.
Using a suitable depth gauge, measure distance Y1.
Apply the formula and determine the shim (12) thickness
to fit in order to obtain the correct taper distance. The
internal diameter of the shims (12) measures approximately 175 mm. They are centred on the rear bore of the hand brake unit. Release the pinion/hand brake unit assembly from the
service tool. Visually note the position of the shims (3) (12). Prepare
the elements for the hand brake mechanism and
refit the pinion/hand brake unit assembly.
