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1. K1009096E Shop Manual
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change materials on previously sold products. It is recommended that consumers periodically contact their
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This documentation may include attachments and optional equipment that is not available in your
machine's package. Please call your distributor for additional items that you may require.
Illustrations used throughout this manual are used only as a representation of the actual piece of
equipment, and may vary from the actual item.
Shop Manual
K1009096E
Serial Number 5001 and Up
DX420LC

2. Table of Contents
Page I
1Table of Contents
Safety
Track Excavator Safety......................................................................... SP000256
Specifications
Specification for DX420LC.................................................................... SP000257
General Maintenance
General Maintenance Procedures........................................................ SP000016
Standard Torques................................................................................. SP000017
Upper Structure
Cabin .................................................................................................... SP000018
Counterweight....................................................................................... SP000265
Fuel Tank.............................................................................................. SP000264
Swing Bearing....................................................................................... SP000262
Swing Reduction Gear.......................................................................... SP000249
Lower Structure and Chassis
Track Assembly .................................................................................... SP000263
Air Conditioner...................................................................................... SP000025
Engine and Drive Train
Drive Coupling (Main Pump)................................................................. SP000026
Hydraulics
Hydraulic System Troubleshooting, Testing and Adjustment ............... SP000273
Accumulator.......................................................................................... SP000028
Center Joint (Swivel)............................................................................. SP000181
Cylinders............................................................................................... SP000030

3. Table of Contents
Page II
Swing Motor.......................................................................................... SP000261
Travel Motor (With Gearbox) ................................................................ SP000266
Main Pump............................................................................................ SP000186
Control Valve (KVMG-400-DA)............................................................. SP000187
Remote Control Valve (Work Lever / Joystick)..................................... SP000189
Travel Control Valve (With Damper)..................................................... SP000070
Solenoid Valve Assembly ..................................................................... SP000191
Breaker EPPR Valve (Opt) ................................................................... SP000192
Fan Motor (Vane Type)......................................................................... SP000209
Gear Pump (Fan Cooling Drive) ........................................................... SP000208
Fan Cooling Flow In-Out Change Valve ............................................... SP000207
Hydraulic Schematic (DX420LC).......................................................... SP000274
Electrical System
Electrical System .................................................................................. SP000269
Electrical Schematic (DX420LC) .......................................................... SP000275
Attachments
Boom and Arm...................................................................................... SP000040
Bucket................................................................................................... SP000041

4. Center Joint (Swivel)
Page 5
SP000181
SAFETY PRECAUTIONS
APPLICABLE MODELS
The contents of this section apply to the following models and
serial number ranges.
CAUTION!
Follow all safety recommendations and safe shop practices
outlined in the front of this manual or those contained
within this section.
Always use tools and equipment that are in good working
order.
Use lifting and hoisting equipment capable of safely
handling load.
Remember, that ultimately safety is your own personal
responsibility.
MODEL SERIAL NUMBER RANGE
DX340LC 5001 and Up
DX420LC 5001 and Up
DX480LC 5001 and Up
DX520LC 5001 and Up

5. SP000181Center Joint (Swivel)
Page 6
GENERAL DESCRIPTION
The center joint (swivel) is designed to allow hydraulic oil from
the upper structure to flow to components in the lower structure.
It is capable of allowing continuous 360° rotation of the upper
structure in relationship to the lower structure.

6. Center Joint (Swivel)
Page 7
SP000181
Center Joint Disassembly Diagram
Figure 1
Reference
Number
Description
1 Body
2 Shaft
3 Cover
4 Spacer
5 Shim
6 Wear Ring
7 Slipper Seal
8 O-ring(1AP 120)
9 O-ring(1BP 100)
10 O-ring(1BG 120)
Reference
Number
Description

7. SP000181Center Joint (Swivel)
Page 8
DISASSEMBLY
1. Set PF3/4 eye bolts on the cover drain port and use a hoist
to move it to a workplace.
2. Remove active oil remaining on each port with air.
3. Use a 19 mm spanner to loosen spacer bolts and remove
the cover and O-rings (1BG120).
4. Use a 17 mm spanner to disassemble the spacer and the
shim.
CAUTION!
It is recommended to use a hoist or a similar device for it is
heavy.
CAUTION!
Remove active oil and wash it out before starting
disassembly.
CAUTION!
It should be disassembled after its active oil is cool enough
after it is removed from the system for its active oil is very
hot.
Figure 2
Figure 3
CAUTION!
Care should be taken not to make a flaw on the surface
of the shaft when disassembling the body of the shaft
assembly.

8. Center Joint (Swivel)
Page 9
SP000181
5. Disassemble the body from the spindle assembly.
A. It can be disassembled easily by fixing the spindle
assembly, tightening at least 2-12 mm eye bolts on
the body, and lifting it with a hoist slowly.
B. Or, it may be disassembled by setting the continuous
thread studs on the spindle drain port as shown in the
figure.
6. Separate the body into 6 slipper seals, 1 wear ring, and 1
O-ring.
7. Remove the PT and PF plugs sealing the shaft.
• Internal sealing PF 3/4: 12 mm wrench.
• External sealing PT3/8: 8 mm Wrench.
Figure 4
Figure 5
CAUTION!
Care should be taken not to damage the inside of the
body because it is likely to be damaged when
disassembling the slipper seal. It may be
disassembled more easily with a driver whose tip is
bent as shown in the figure below.
Figure 6

9. SP000181Center Joint (Swivel)
Page 10
8. Remove foreign substance at every pieces disassembled
and wash them out.
9. Replace disassembled O-rings and slipper seals with new
ones, for they cannot be reused.
CAUTION!
The inside of the body should be air washed and rust-
proof treated after washing it, as its material is subject
to rust.

10. Center Joint (Swivel)
Page 11
SP000181
REASSEMBLY
1. Wrap the Teflon tape around the PT3/8 about 6 times.
2. Assemble the PT and PF plugs into the washed shaft.
3. Assemble the sliper seal, the wear ring, and the O-ring into
the body.
4. Assemble the 1AP - 120 O-ring the outside of the body.
CAUTION!
Apply active oil to every functional (moving) part before
assembly to reduce any assembly friction as much as
possible.
Figure 7
Internal sealing PF3/4: 12 mm wrench External sealing PT3/8: 8 mm wrench
Engagement torque: 15±1.09 Kg m Engagement torque: 4.5 ~ 9.5 kg m
Figure 8
CAUTION!
After assembling the sliper seal, a manual test should
be performed to ensure that every part is assembled
for its position properly.

11. SP000181Center Joint (Swivel)
Page 12
5. Fix the position of the shaft and press the body carefully
into shaft with both being parallel each other.
6. Use a plastic (or rubber) hammer to tap the body until it is
inserted completely.
7. Engage the shim, the spacer, and the spacer bolts on the
top of the shaft.
8. Use a torque wrench to tighten spacer bolts at 5 ~ 6 kg m
CAUTION!
For any sliper seal which is protruded, press it with
finger to seat it in its position. Care should be taken
when using a driver or a metal tool, which may cause
damage to it.
CAUTION!
Applying active oil to the surface of the shaft enables
the assembly without any damage to the sliper seal.
Figure 9
CAUTION!
Tap the body in a zigzag pattern that it does not tilt to
one side.
Figure 10

12. Center Joint (Swivel)
Page 13
SP000181
9. Set the O-ring (1 BG 120) in its place and assemble the
cover in the direction as shown in the figure.
10. Engage the cover bolt (M 12) at torque of 10 ~ 12.5 kg m.
11. Return the O-ring (1 AP 120) assembled to the outside of
the body to its original position.
Figure 11
CAUTION!
After the completion of the assembly, a start-up and a
rotation torque tests should be performed for the
sliper seal to seat in its place properly.

13. SP000030Cylinders
Page 22
DISASSEMBLY
1. Following removal of cylinder from excavator attachment,
support cylinder on some type of sturdy work platform and
drain all oil. Rotate cylinder so that piping ports are on top,
to allow trapped air to vent.
2. Position piston rod so that it is extended approximately one
half meter (20").
3. Remove bolts (7) on the end of cylinder.
NOTE: Wrap a cloth or other protective material around
piston rod, to avoid possibility of accidentally
scratching or scoring rod surface while
fasteners are being loosened and removed.
Component parts (numbered in parentheses)
are keyed to Figure 4.
CAUTION!
Vent air from the hydraulic system before disconnecting
cylinder piping connections. Use the lever on the reservoir,
while the engine is running. Discharge the hydraulic
accumulator and vent residual tank pressure after the
engine is shut off. Pour clean replacement fluid back into
the system if excessive fluid is lost.
Figure 12
Figure 13
Figure 14

14. Cylinders
Page 23
SP000030
4. Tap two bolts into cover of cylinder head, 180° apart.
Tighten them in a staggered, even sequence, to back off
piston rod end cover from edge of cylinder wall. Look for
adequate clearance between cover and end of cylinder
wall before using a plastic or other soft-faced hammer for
final disassembly.
5. Begin withdrawing piston rod assembly, away from
cylinder. Attach a lifting support when final 1/3 of rod is still
inside barrel of cylinder. Prepare support blocks for piston
rod before it has been completely withdrawn.
6. Lower piston rod to support blocks and detach wear ring
(outer surface) (18) from end of rod.
7. Immobilize piston rod by inserting a wooden or other
nonscoring, nonmetallic support through end of rod.
Figure 15
Figure 16
Figure 17
Figure 18

15. SP000030Cylinders
Page 24
8. Remove set screw using socket wrench.
9. Fabricate or purchase a piston nut removal wrench.
(Dimensions are called off at beginning of this procedure.
This tool may also be ordered through your local DOOSAN
Parts distributor). Remove nut from end of piston.
10. Use second piston tool described at beginning of this
procedure to separate piston. Detach cushion ring (15),
taking care not to damage cushion ring.
11. Use a plastic hammer to evenly pull off rod cover (9) from
end of piston rod. Be careful not to damage rod bushing (6)
and dust wiper, U-packing and other seals.
HAOF340L
Figure 19
Figure 20
Figure 21
Figure 22

16. Cylinders
Page 25
SP000030
12. Use a dull, rounded tip tool to pry off O-ring (11) and
backup ring (12).
13. Find a screwdriver with an appropriate width tip to facilitate
removal of slipper seal (19), wear ring (18) and slide ring
(17) from piston (16).
14. Remove O-ring (20) and backup ring (21) from cylinder
head.
15. During disassembly of cylinder head, be careful not to
damage buffer seal (5) and U-packing (4).
HAOF37OL
Figure 23
Figure 24
HAOF38OS
Figure 25
HAOF39OL
Figure 26

17. SP000030Cylinders
Page 26
16. Disassemble retaining ring (3) and dust wiper (2). Separate
retaining ring (8) and rod bushing (6).
17. Force out pin bushing (1) from body of cylinder.
Figure 27
Figure 28

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19. Cylinders
Page 27
SP000030
REASSEMBLY
NOTE: Reassemble the subassemblies of the cylinder in the
following order:
1. Body of the cylinder.
2. Piston rod.
3. Piston assembly.
4. Cylinder head assembly.
1. Reassemble pin bushing (1) to piston rod (13) and body of
cylinder (14).
2. Following reassembly of rod cover components, install the
dust wiper (2) and rod bushing (6) to the rod cover (9).
Insert retaining rings (3 and 8).
IMPORTANT
Replace any part that shows evidence of damage or
excessive wear. Replacement of all O-rings and flexible
seals is strongly recommended. Before starting the cylinder
reassembly procedure, all parts should be thoroughly
cleaned and dried, and/or prelubricated with clean
hydraulic fluid. Prepare the work area beforehand to
maintain cleanliness during the reassembly procedure.
Figure 29
Figure 30

20. SP000030Cylinders
Page 28
3. Prelubricate O-rings and seals before reassembly (Figure
31).
4. Before starting to rebuild piston assembly, heat slipper seal
for 5 minutes in an oil bath warmed to 150° - 180°C (302° -
356°F). Use special slipper seal jig (third item in list of
specialized tools at the beginning of this procedure) to
attach seal. Cool seal by pushing a retracting jig against
seal for several minutes. Apply a strip of clean, see-
through sealing tape around slipper seal to keep it free of
dust.
5. Immobilize piston rod on solid support blocks. Assemble
O-ring (20) and backup ring (21). Prepare to attach rod
cover assembly to piston rod. Push rod cover by tightening
piston nut (22).
6. Assemble cushion ring (15) and attach piston assembly to
piston rod.
Figure 31
Figure 32
Figure 33
Figure 34

21. Cylinders
Page 29
SP000030
7. Use specially fabricate or factory sourced tool to tighten
piston nut (22).
8. Assemble wear ring (18), slide ring (17) and set screw (23)
to piston assembly.
9. Immobilize body of cylinder before reassembly.
Preapply fastener locking compound (Loctite #242 or #243 or an
alternate manufacturer's equivalent product) to all end cover
retaining bolts. Wrap a protective cushion around end of rod
while tightening fasteners, to prevent possible damage to
polished surface of rod, should a wrench slip during retightening.
Figure 35
Figure 36
Reference
Number
Description
1 Set Screw
Figure 37
Figure 38