The present invention relates generally to brake systems, and in
particular to a wet disc brake unit for an off-highway vehicle.
Vehicle friction brake systems, and other friction systems, such
as clutches, include a plurality of friction members, some of which rotate with
respect to the others. Braking is obtained by the frictional engagement between
the relatively rotating members. Many of these devices utilize fluid pressure
actuated pistons for accomplishing the required movement in the friction components
to obtain the frictional engagement. The piston or pistons generally include an
effective pressure area to which fluid pressure is applied to create a force urging
the piston in a brake applying or brake releasing direction. The prior art has
suggested a variety of piston retraction mechanisms to obtain brake release.
In off-highway apparatus such as construction vehicles and mining
equipment, a brake system is necessary which can bear up under the severe operating
conditions. The brakes on these vehicles are often subjected to extremely large
braking torques and braking applications for extended periods of time. The brakes
are employed not only to stop vehicle motion, but are utilized in retarding vehicle
speed when traveling downhill. The brake unit must have the capability of dissipating
extremely large kinetic energies developed due to the large vehicle mass, especially
when the brakes are applied for extended time periods. For this and other reasons,
a brake system of the multi-disc type is often chosen for this application.
A typical multi-disc brake includes a series of interleaved, non-rotatable
and rotatable friction disc plates. The rotatable disc plates are operatively connected
to the wheel and the non-rotatable disc plates are coupled or "grounded" to the
axle housing or other non-rotating wheel support structure. Both the rotatable
and non-rotatable disc plates are mounted for axial movement with respect to the
axle and are enclosed within a brake housing. Spline connections are generally
employed to couple the plates and the brake member to which they are operatively
engaged. To obtain braking in this type of brake, the interleaved disc plates
must be compressed so that their friction surfaces engage to convert the mechanical
energy associated with the rotation of the rotatable disc plates into heat, which
is then dissipated. The stack of interleaved disc plates is generally compressed
between a wall of the brake chamber in which it is enclosed, and a movable pressure
plate. In at least some brake units, a fluid pressure operated piston or pistons
engage the pressure plate and move it axially into abutting contact with the outermost
friction disc causing subsequent engagement of all the disc plates.
To increase the heat dissipation rate of multi-disc brakes, the discs
are sometimes operated in a fluid medium which flows through the brake housing,
absorbing heat from the friction discs and then transfers it to a remote heat
exchanger. The multi-disc brake, coupled with a cooling system, provides a brake
system having an extremely large torque capacity in a relatively small package.
Some proposed systems have suggested the use of separate retraction
springs coupled to the actuating piston to obtain brake release, so that when the
pressurized fluid acting on the piston was terminated, the springs would force
the piston to its released position. Other systems would employ separate fluid
operated retraction pistons to effect the same result. Still others have suggested
the utilization of a pressure plate biased towards brake application by a plurality
of springs. The piston is arranged to oppose the spring applied force when the
piston is subjected to fluid pressure. This type of brake is often termed a "spring
applied hydraulically released"" or "SAHR" brake.
The emergency application of the vehicle brakes upon failure of the
fluid pressure system has been addressed by some prior art brake systems. Suggested
mechanisms have included spring biased emergency pistons normally held in a released
position by a separate fluid pressure system. Upon brake failure, the emergency
pressure system would deplete the pressure applied to the spring biased piston
allowing it to engage the vehicle brakes. Other systems have used redundant fluid
pressure operated pistons supplied with separate sources of fluid pressure. In
a SAHR type brake, a failure in the hydraulic system causing a loss in hydraulic
pressure to the piston results in the application of the brake by the biasing
springs. In many of these suggested systems, the apparatus added significant complexity
to the brake housing and more importantly, adversely affected the brake assembly
size, making them unsuitable for many vehicle applications having brake size constraints.
In those systems which would suggest the use of separate source of pressurized
fluid, the control system necessary to effect reliable operation would be costly
to manufacture and maintain.
Disclosure of the Invention
The present invention provides a new and improved wet disc brake
unit for a wheeled vehicle capable of generating a relatively high braking torque
and having a relatively large energy absorption capacity while retaining a relatively
small envelope size allowing it to be used on vehicles having small wheels such
as mining vehicles.
According to the preferred and illustrated embodiment, the wet disc
brake unit includes a piston housing that supports an annular piston for reciprocating
movement. A disc housing is secured to the piston housing and defines a disc chamber
in which a plurality of interleave, rotating and non-rotating discs are located.
As is known the discs form a disc pack. An annular pressure plate is disposed
adjacent to the disc pack and is operative to clamp and unclamp the discs in order
to generate braking torque. Movement of the pressure plate towards and away from
the disc pack is controlled by the annular piston.
According to a feature of the invention, a pressure plate-to-disc
seal is used to inhibit the flow of coolant between the pressure plate and the
disc that is immediately adjacent the pressure plate. In the preferred embodiment,
the outermost disc of the disc pack, which is contacted by the pressure plate,
is non-rotatable with respect to the pressure plate and hence very little heat,
if any is generated between these brake members during braking. The disclosed
seal arrangement inhibits coolant flow between the non-rotating disc and the pressure
plate when the brake is in a released position.
In the preferred construction, the seal arrangement comprises an
annular seal slidably carried on a cylindrical surface defined by the pressure
plate. A radial end of the annular seal abuttably engages the first disc and is
urged towards abutting contact by a spring means acting between the pressure plate
and the seal. In the preferred construction, the spring comprises a Belleville-type
spring which engages an opposite radial face of the annular seal.
With the disclosed seal arrangement, the flow of coolant is encouraged
to flow between the interleaved non-rotating and rotating discs between which heat
is generated during braking. Since the outboard disc in the disclosed embodiment
does not rotate with respect to the pressure plate, heat is not generated between
these two components and hence, any coolant flowing between these members when
the brake is released would have very little heat transferred to it. With the
disclosed sealing arrangement, coolant flow in areas where heat is generated is
encouraged and enhanced.
According to the exemplary embodiment, the disclosed brake unit is
of the spring-applied, hydraulically released (SAHR) type brake. In this type of
brake, springs are used to apply the brakes and hydraulic pressure, under the
control of a brake control valve, is used to release the brake. In this type of
brake unit, the brakes are applied by a selectively reducing brake pressure in
order to allow the springs to apply the brake.
In the disclosed and preferred embodiment, the pressure plate is
urged towards engagement with the disc pack by a plurality of springs located in
spring chambers formed in the disc housing. The brake piston is located on the
opposite side of the disc pack and applies a force to the pressure plate which
counters the spring-applied force.
According to a feature of the invention, the pressure plate is formed
with a plurality of integrally formed stand-offs which extend axially from the
pressure plate into abutting contact with the piston. In the preferred embodiment
of this feature, the non-rotating or reaction discs are formed with peripheral
slots through which the stand-offs extend in order to engage the piston. Preferably,
the non-rotating discs include teeth that mate with internal splines formed in
the brake disc housing which inhibit the reaction discs from rotating with respect
to the housing and the pressure plate.
The slots formed in the discs merely form clearance spaces for the
stand-offs. The reaction discs, in the preferred embodiment, do not engage the
pressure plate stand-offs. According to this feature, as the piston, under the
influence of pressurized fluid, moves towards the disc pack, the pressure plate
stand-offs are engaged and the piston force opposes a spring force in order to
move the pressure plate away from the disc pack, thereby releasing the brake.
The brake is applied by selectively reducing the pressurized fluid applied to the
piston to enable the spring biased pressure plate to engage and apply a clamping
force to the disc pack.
According to the invention, coolant for cooling the discs that comprise
the disc pack is introduced into the brake unit via an inlet that communicates
with a peripheral region of the discs. Coolant admitted to the peripheral region
flows between the disc members and into a central receiving region located near
the inner periphery of the discs. The coolant then flows from the central region
to an outlet through which the coolant is discharged. As is conventional, the
coolant flows to a heat exchanger where it releases the heat absorbed during its
traversal of the brake unit.
In the preferred embodiment, the coolant outlet is defined by one
of the spring chambers, preferably a spring chamber located near or at the twelve
o' clock position on the brake housing.
To further control coolant flow through the brake housing, a peripheral
seal is used to seal an interface between the pressure plate and the brake disc
housing. Preferably, an O-ring type seal is carried by a groove defined in the
pressure plate which sealingly engages a cylindrical wall which slidably supports
the pressure plate for reciprocating movement towards and away from the disc pack.
According to a further aspect of this feature, an annular groove is defined between
the pressure plate and housing which serves to distribute coolant throughout the
peripheral region of the brake housing. With the disclosed arrangement, coolant
introduced into the brake housing through the cooling inlet, is distributed via
the distribution groove in the peripheral region of the disc pack. From there,
the coolant flows through the non-rotating and rotating disc members (coolant flow
is inhibited between the pressure plate and the outermost disc member), finally
being received in a central region from where it is communicated to the spring
chamber that defines the coolant outlet.
According to a further feature of the invention, the brake disc housing
includes rigidizing structure engageable with mating structure on the piston housing
which interengage upon assembly to control and inhibit deflection in the piston
chamber. Preferably, an extension formed on a radial face of the brake housing
engages and surrounds a stepped portion formed on the piston housing which resists
radial movement in walls that define the piston chamber in the piston housing.
In effect, a socket/projection type interconnection is established.
According to a further feature of the invention, at least some of
the spring chambers include a pressure plate releasing element which is operable
from outside the brake housing in order to retract the pressure plate should fluid
pressure to the piston be unavailable. In the preferred embodiment, the retraction
mechanism includes a pull rod attached to the pressure plate which extends axially
towards an opening defined in the spring chamber. A plug member normally seals
the aperture. Should manual release of the brake be necessary, the plug member
is removed and a suitable retraction member, such as a retraction bolt, is threaded
into the pull rod thereby pulling the pressure plate away from the disc pack (against
the spring force) thereby releasing the clamping force on the disc pack.
According to still another feature of the invention, the pressure
plate is formed with a shoulder or lip on its inner periphery which is engageable
by a disc member alignment tool during assembly. According to this aspect of the
invention, when a brake unit is installed on the vehicle and is to be reassembled,
the assembly tool, which is held to the axle by a mounting member, engages the
inner lip formed on the pressure plate. The assembly tool also includes mating
splines for engaging and aligning the non-rotating and rotating discs located in
the disc chamber. Jacking bolts forming part of the assembly tool push the pressure
plate in the retracted direction against the force of the brake-applying springs,
while maintaining alignment of the discs.
The piston housing is then mounted to the disc housing and once mounted,
the tool is manipulated to release the pressure plate to allow the springs to clamp
the pressure plate against the disc pack. The spring force applied through the
pressure plate maintains the non-rotating and rotating discs in alignment to enable
the assembly tool to be removed. A wheel member, including a splined drive member,
can then be remounted on the axle in driving engagement with the rotating discs.
In the present invention, a brake unit having relatively high torque
capacity with minimal envelope diameter is provided. The disclosed brake unit is
capable of fitting applications with small wheel sizes without sacrificing brake
Additional features of the invention will become apparent and a fuller
understanding obtained by reading the following detailed description made in connection
with the accompanying drawings.
Brief Description of the Drawings
Best Mode for Carrying Out the Invention
- Figure 1 is a fragmentary, sectional view showing a brake unit and attached
wheel assembly constructed in accordance with the preferred embodiment of the invention;
- Figure 2 is a sectional view of the brake unit showing an assembly tool in
position which facilitates assembly of the brake unit while mounted to a vehicle;
- Figure 3 is an inside end view of the brake unit with parts removed for clarity;
- Figure 4 is an exploded, sectional view of the apparatus shown in Figure 2;
- Figure 5 is a elevational view of a non-rotating disc forming part of the brake
- Figure 6 is a elevational view of a rotating disc forming part of the brake
Figure 1 illustrates in cross-section, a wet disc brake unit 10 embodying
the present invention. In the illustrated embodiment, the brake unit 10 is attached,
in a conventional manner, to an axle housing 12 by a plurality of mounting bolts
14 which extend through apertures 15 formed in the brake housing. The brake unit
10 is of the spring applied/hydraulically released (SAHR) type brake unit.
The axle housing 12 rotatably supports a wheel hub 16 via roller
bearing 18. As will be explained, the wheel hub 16 is interconnected with the brake
unit 10 such that actuation of the brake unit, retards rotation in the wheel hub
16 and hence, the vehicle that it forms part of.
Referring also to Figure 2, the brake unit 10 includes an end cap
10a bolted to a brake housing 10b by a plurality of assembly bolts 20 (see also
Figures 3 and 4). In the illustrated and preferred construction, the end cap 10a
mounts an annular piston 22 in an annular channel 24 integrally formed in the
end cap. A pair of annular seals 25, 26 carried in grooves 25a, 26a sealingly engage
the piston 22. As viewed in Figure 2, the annular piston 22 is reciprocally mounted
within the groove and defines a piston chamber 28 between an outer end face 22a
and the annular groove. Pressurized fluid, communicated by way of feed passage
30 and branch passage 32 acts on the piston end face 22a and urges the piston 22
towards the right as viewed in Figure 2. The supply passage 30 is defined by laterally
aligned bores 30a, 30b formed in the piston housing 10a and brake housing 10b.
The passage terminates in a port 34 (shown in Figure 3) and is connected to a brake
conduit (not shown) forming part of the brake control system. A bleed port 35
is also provided.
When assembled, the housing 10b defines a disc chamber 40 in which
a plurality of interleave, non-rotating and rotating brake discs are disposed 41a,
41b, respectively. The non-rotating discs are fixed to or "grounded" to the brake
housing 10b by means of internal splines 42 formed on the inner periphery of the
brake housing 10b. The non-rotating discs include matching splines 43 (see Figure
5) which engage the brake housing splines, as is conventional. The rotating discs
41b include internal teeth 45 (see Figure 6) which, as seen in Figures 2 and 3,
engage splines 44 formed on a hub extension 16a. As should be apparent, the rotatable
hub 16 is coupled to the rotating discs via the splines 44. The spline connection
inhibits relative rotation between the hub 16 and the rotating discs while allowing
relative axial movement between the discs and the hub.
According to the invention, the piston housing 10b also reciprocally
mounts an annular pressure plate 60. The pressure plate 60 defines an internal,
force applying wall 60a which is abuttably engageable with the rightmost non-rotating
disc 41a (as viewed in Figure 1). The discs 41a, 41b, which form a disc pack,
retard rotation in the wheel hub 16 whenever the discs are compressed between the
pressure plate wall 60a and an end wall 64 defined by the piston housing 10a.
The extent to which the discs 41a, 41b are compressed determines the braking torque
applied to the wheel hub 16.
According to the invention, the pressure plate 60 is urged, by a
plurality of springs 70, 72, towards a brake applying position, i.e. a position
at which it abuttably engages the rightmost non-rotating disc and effects compression
of the disc pack between itself and the end wall 64. The springs 70, 72 are located
in spring pockets 74 defined by the brake housing 10b. The pockets 74 are radially
distributed around the brake housing 10b and together apply a uniform brake applying
force to the pressure plate 60. In the illustrated embodiment, each spring pocket
74 mounts inner and outer, coaxially aligned coil springs 70, 72. It should be
noted that other types of springs and spring arrangements are contemplated by the
present invention. For example for some applications, a single coil spring in
each spring pocket 74 may be suitable.
According to the invention, the annular piston 22 applies brake releasing
forces to the pressure plate 60 by means of a plurality of stand-offs 80 which
are integrally formed with the pressure plate 60. The stand-offs 80 extend laterally
through aligned, peripheral slots 82 (see Figures 3 and 5) formed in the non-rotating
discs 41a and abuttably engage a piston end face 22b. The axial extent of the
stand-offs 80 is preferably greater than the axial width of the discs 41a, 41b
when the discs are engaged. The rotating discs 41b have a radial dimension less
than the radial dimension of the non-rotating discs 41a and such that their peripheries
83 (see Figure 6) terminate short of the pressure plate stand-offs 80.
Referring to Figure 5, the construction of a non-rotating disc or
reaction plate 41a is illustrated. As indicated above, each non-rotating disc 41a
includes a plurality of peripheral slots 82. As seen best in Figure 5, the slots
82 define a plurality of peripheral, toothed segments 84, each defining a plurality
of teeth 43 which in turn, engage the internal splines 42 defined by the brake
housing 10b. In the disclosed construction, eight peripheral slots 82 are defined
in each disc 41a and in turn, each disc includes eight toothed segments 84.
As indicated above, the rotating discs 41b have a radial dimension
such that the peripheral edge 83 (see Figure 6) of the rotating discs 41b have
a radial extent substantially equal to or less than the radial extent of the base
82a of the slots 82 see Figure 5). Accordingly, in the illustrated construction,
the pressure plate 60 includes eight stand-offs which extend axially through the
slots 82 and are dimensioned such that they clear and do not interfere with the
non-rotating discs 41a or the rotating discs 41b.
With the disclosed brake construction, the application of pressurized
fluid to the piston chamber 28 urges the piston towards the right (as viewed in
Figure 1) which then applies a force to the pressure plate 60 in opposition to
the brake applying forces exerted by the springs 70, 72. The brake is released
by applying sufficient pressurized fluid to the brake chamber 28 to fully counter
the spring applied force and to move the pressure plate 60 towards the right as
viewed in Figure 1, thereby unclamping the rotating and non-rotating discs 41a,
To effect braking action (under normal service), pressurized fluid
in the brake chamber 28 is released to allow the spring 70, 72 to urge the pressure
the plate 60 into clamping engagement with the discs 41a, 41b. The resulting frictional
engagement between the non-rotating and rotating discs applies a braking torque
to the hub 16. The extent of braking torque is proportional to the extent of force
applied by the pressure plate 60. Consequently, the extent of braking is controlled
by selectively releasing pressure (under normal operating conditions) in the piston
Brake systems and associated brake treadle valves (not shown) are
known which operate to control the depletion of fluid pressure in a chamber as
a function of pedal actuation. With these types of brake control systems, depression
of the treadle valve by the operator effects the reduction of pressure in the brake
piston chamber 28, the extent of which depends on the extent of brake pedal actuation.
With the disclosed brake, a failure in the hydraulic system causes application
of the brake since a resulting reduction in fluid pressure in the brake piston
chamber 28 will allow the springs 70, 72 to move the pressure plate 60 into clamping
engagement with the discs 41a, 41b.
Turning now to Figure 4, the pressure plate springs 70, 72 for applying
the brake are located in the spring pockets or spring chambers 74 defined by the
disc housing 10b. In the disclosed embodiment, fifteen (15) spring chambers 74
are defined in the housing 10b. According to the invention, individual spring
chambers 74 (as opposed to a common annular spring groove ) are defined with each
chamber 74 including a bridging segment 74a extending between an outer portion
of the brake housing 10b and an inner portion. These bridging segments 74a add
rigidity to the overall brake unit and act as radial ribs extending across an inner
face of the brake housing 10b.
According to a feature of the invention, coolant is circulated throughout
the braking chamber 40 to remove heat generated during braking. In the preferred
embodiment, coolant is communicated to the disc chamber 40 by way of a passage
100 that terminates, at its inner end, in a port 100a to which a coolant feed conduit
(not shown) is connected. An annular groove 102 defined by the brake housing communicates
with the outer end of the coolant passage 100 and distributes coolant throughout
the brake chamber 40. According to a feature of the invention, an annular sealing
ring 110 is carried in a pressure plate groove 112 and sealingly engages an inside
wall of the brake chamber 40. The seal ring 110 inhibits the flow of coolant past
the pressure plate 60 and into the spring chambers 74. Instead, the coolant flows
from the annular groove 102 into a peripheral, disc pack region 120 (shown on Figure
2). From there, the coolant flows in a general radial direction between the discs
41a, 41b, in coolant grooves formed in at least some of the discs.
According to the preferred embodiment, a seal is provided between
the pressure plate 60 and the adjacent non-rotating disc 41a to inhibit the flow
of coolant between these two components. It should be recognized, that the heat
generated during braking is generated between the frictional surfaces of the rotating
and non-rotating discs. In order to maximize efficiency of the cooling system,
the flow of coolant is controlled so that in general, it is confined such that
it is encouraged to flow between the frictional surfaces of the non-rotating and
rotating discs 41a, 41b. To achieve this feature, a spring loaded, annular seal
126 (see Figure 1) is carried by the pressure plate 60 and sealingly engages the
adjacent, non-rotating disc 41b. In the preferred embodiment, the seal 126 is urged
toward sealing contact with the adjacent non-rotating disc 41a by a Belleville
spring 130. Whenever the pressure plate 60 is moved into its retracted position
whereby the disc pack is released, the Belleville spring 130 acting upon the face
seal 126, maintains contact between the seal and the pressure plate 60. As a result,
the flow of coolant between the non-rotating pressure plate 60 and the adjacent
non-rotating disc 41a is inhibited. The preferred face seal is made from a glass
filled teflon or similar material.
The coolant, after traveling between the disc pack, flows through
ports or passages formed near the hub 16a and then travels towards the spring chambers
74. Referring to Figure 6, in the preferred embodiment, the coolant passages or
ports neat the hub 16a are formed by removing selected teeth 45 from the rotating
discs 41b. In the illustrated embodiment teeth at the locations 45a are removed
from the discs 41b. During brake assembly, the discs 41b are mounted with the
locations 45a aligned so that a passage is formed between the discs 41b and the
hub 16a. Alternately, selected splines from the hub 16a may be removed to define
The coolant leaves the brake unit through an outlet port 136 (see
Figure 3) defined by one of the spring chambers 74. In the preferred embodiment,
the port 136 is defined in a spring chamber 74 located near the top of the unit.
With the disclosed cooling path, highly efficient heat removal is achieved and
the bypassing of coolant around the disc pack, where it is needed most, is inhibited.
As described above, the loss of pressurized fluid, either through
operator action or a failure in the brake system, enables the spring 70, 72 to
apply the brakes. According to a feature of the invention, provision is made to
mechanically release the discs 41a, 41b should pressurized fluid be unavailable.
According to this feature, several spring chambers 74 include an access plug 140.
In the springs chambers that include this access plug, pull rods 142 are connected
to the pressure plate 60. By removing the plugs 140, threaded jack bolts of suitable
length (not shown) can be used to engage the pull rods 142 to retract the pressure
plate 60 thereby releasing the brake to enable the vehicle to be moved. It should
be noted, that permanent bolts can also be provided with suitable seals which
would be used in a similar manner, to pull the pressure plate 60 towards the right
(as viewed in Figure 1) to release the brake in the absence of pressurized fluid.
To further rigidize the overall unit, the end cap 10a is piloted
into the brake housing 10b. In particular, the end cap 10a is formed with a stepped
annular portion or extension 150 which is sized to be received in an annular opening
152 formed in the brake housing 10b. Once assembled, the engagement between the
brake housing 10b and the annular extension 150 formed in the end cap, rigidizes
the piston groove 24 and reduces or inhibits spreading of the inner and outer
walls of the groove 24 due to pressurization of the piston chamber 28.
With the disclosed brake unit construction, access to the disc pack
can be obtained without requiring complete removal of the brake unit. In order
to perform service on the disc pack and/or piston 22, the wheel hub 16 is removed
and then the end cap bolts 20 are removed in order to release the end cap 10a
from the brake housing 10b. Referring to Figure 2, a tool 170 is provided for
facilitating reassembly of the brake unit. As should be apparent, since the pressure
plate 60 is under spring load due to the springs 70, 72 located in the spring pockets
74, the end cap 10a must be installed by compressing the springs during assembly.
Upon reassembly, the disc pack is tightly clamped between the pressure plate 60
and the end wall 64 since pressurized fluid to the piston chamber 28 is absent.
During assembly, the rotating discs 41b must be aligned to enable
mounting of the hub 16a of the wheel hub 16. In order to maintain alignment of
the rotating discs 41b during reassembly, the tool 170 is provided which compresses
the springs 70, 72 and maintains alignment of the rotating discs 41b. In the preferred
embodiment, an alignment member 172 is provided which is engageable with the inner
splines formed on the rotating discs 41b. The pressure plate 60 includes structure
defining a shoulder or lip 176 which is engageable by the alignment member 172.
In the preferred embodiment, the alignment member 172 includes mating
splines 180 which are engageable with the aligned teeth 45 defined by the rotating
discs 41b. The alignment member 172 also defines a shoulder 184 which abuttably
engages the inner lip 176 of the pressure plate 60. A jack plate 190 is held to
the axle spindle by a conventional spindle nut 192 and threadedly mounts a plurality
of jack bolts 194 which extend axially and engage the alignment member (as best
shown in Figure 2). By gradually torquing the jack bolts 194, the alignment member
172 is moved inwardly, pushing the pressure plate 60 in a brake release direction,
thus, compressing the brake applying springs 70, 72. After the end cap or piston
housing 10a and all other components are installed, the jacking force is released
on the alignment member 172 by unthreading the jack bolts 194. Since brake pressure
in the piston chamber 28 is absent, the springs 70, 72 clamp the rotating and
non-rotating discs 41a, 41b between the pressure plate 60 and the end wall 64.
This spring applied force maintains the relative positions between the rotating
and non-rotating discs 41a, 41b allowing the alignment member 172 and jacking
member 190 to be removed from the axle housing 12. The wheel hub 16 can then be
installed onto the axle housing 12 with the splined portion 16a engaging the rotating
discs 41b, as seen in Figure 1.