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1. Original InstructionsCopyright DOOSAN 2012
Serial Number 1001 and Up
Serial Number 50001 and Up (Europe Only)
Shop Manual
DX255LC-3 Excavator
950106-00374E
April 2012
DOOSAN and the DOOSAN logo are registered
trademarks of DOOSAN Corporation in the United
States and various other countries around the
world.

2. Table of Contents
Page I
1Table of Contents
Safety
Track Excavator Maintenance Safety................................................... SP002322
Specifications
Specifications for DX255LC-3............................................................... SP002547
General Maintenance
General Maintenance Instructions........................................................ SP002454
Standard Torques................................................................................. SP002404
Upper Structure
Cabin .................................................................................................... SP002324
Counterweight....................................................................................... SP002548
Fuel Tank.............................................................................................. SP002549
Fuel Transfer Pump (Option)................................................................ SP002550
Swing Bearing....................................................................................... SP002329
Lower Structure and Chassis
Track Assembly .................................................................................... SP002551
Engine and Drivetrain
Engine Coolant Heater (Option) ........................................................... SP002328
Drive Coupling (Main Pump)................................................................. SP002586
Hydraulics
Hydraulic System Troubleshooting, Testing and Adjustment ............... SP002597
Accumulator.......................................................................................... SP002455
Center Joint (Swivel)............................................................................. SP002456
Cylinders............................................................................................... SP002587

3. Table of Contents
Page II
Swing Device........................................................................................ SP002588
Travel Device........................................................................................ SP002590
Main Pump............................................................................................ SP002591
Gear Pump ........................................................................................... SP002500
Main Control Valve ............................................................................... SP002403
Remote Control Valve (Work Lever / Joystick)..................................... SP002395
Travel Control Valve (with Damper)...................................................... SP002381
Solenoid Valve Assembly ..................................................................... SP002406
Breaker EPPR Valve (Option) .............................................................. SP002458
Hydraulic Schematic (DX255LC-3)....................................................... SP002589
Electrical System
Electrical System .................................................................................. SP002337
Electrical Schematic ............................................................................. SP002508
Attachments
Boom and Arm...................................................................................... SP002592
Bucket................................................................................................... SP002506

4. SP002322
Page 1
Track Excavator Maintenance Safety
SP002322
TRACK EXCAVATOR MAINTENANCE SAFETY
SP002322
Track Excavator
Maintenance
Safety
Edition 3

5. SP002322
Page 5
Track Excavator Maintenance Safety
SAFETY INSTRUCTIONS
APPLICABLE MODELS
The contents of this section apply to the following models and
serial number ranges.
WARNING
AVOID DEATH OR SERIOUS INJURY
Instructions are necessary before operating or servicing
machine. Read and understand the Operation and
Maintenance Manual and signs (decals) on machine. Follow
warnings and instructions in the manuals when making
repairs, adjustments or servicing. Check for correct
function after adjustments repairs or service. Untrained
operators and failure to follow instructions can cause death
or serious injury.
MODEL SERIAL NUMBER RANGE
DX140LC-3 1001 and Up, 50001 and Up
DX180LC-3 1001 and Up, 50001 and Up
DX225LC-3 1001 and Up, 50001 and Up
DX255LC-3 1001 and Up, 50001 and Up
DX300LC-3 1001 and Up, 50001 and Up
DX340LC-3 1001 and Up, 10001 and Up
DX350LC-3 1001 and Up, 10001 and Up
DX380LC-3 10001 and Up
DX420LC-3 10001 and Up
DX490LC-3 10001 and Up
DX530LC-3 10001 and Up

6. SP002322Track Excavator Maintenance Safety
Page 6
SAFETY MESSAGES
Safety messages and safety decals included in this manual and
on the machine provide instructions how to operate, service and
maintain the machine. Safety messages and safety decals
indicate potential hazards and describe safety precautions
required to avoid hazards. Operator and maintenance personnel
should read and understand these safety messages and decals
before beginning operation or maintenance.
Signal Words
The signal words "DANGER", "WARNING", "CAUTION" are
used throughout safety messages and safety decals in this
manual or on the machine. They indicate an existence of, and
the relative seriousness of, a hazard. All three indicate that a
safety risk is involved. Observe the precautions indicated
whenever a Safety Alert Symbol is present, no matter which
signal word appears next to it.
SAFETY ALERT SYMBOL
Be Prepared - Get to Know All Operating and Safety
Instructions.
This is a Safety Alert Symbol. Wherever it appears in this
manual or on safety decals on the machine, you must be
alert to the potential for personal injury or accidents.
Always observe safety precautions and follow
recommended procedures.
DANGER
DANGER - This signal word is used on safety messages and
safety labels and indicates an imminently hazardous situation
which, if not avoided, will result in death or serious injury.
WARNING
WARNING - This signal word is used on safety messages and
safety labels and indicates a potentially hazardous situation
which, if not avoided, could result in death or serious injury.

7. SP002322
Page 7
Track Excavator Maintenance Safety
Other Signal Words
In addition to safety signal words, the following signal words are
used to indicate proper and effective use of machine.
The word "NOTE" identifies information for effective use.
SAFETY DECALS
Location of safety labels (decals) can vary from unit to unit.
Refer to appropriate Operation and Maintenance Manual, and
parts manual for your unit.
Always replace damaged or faded decals.
CAUTION
CAUTION - This signal word is used on safety messages
and safety labels and indicates a potentially hazardous
situation which, if not avoided, could result in minor or
moderate injury.
IMPORTANT
This signal word identifies procedures which must be
followed to avoid damage to machine.

8. SP002322Track Excavator Maintenance Safety
Page 8
GENERAL
Safe Operation is Operator's
Responsibility
Only trained and authorized personnel should operate and
maintain the machine.
Follow all safety rules, regulations and instructions when
operating or performing maintenance on machine.
• Do not operate machine if you are under the influence of
drugs or alcohol. An operator who is taking prescription
drugs must get medical advice to determine if he or she
can safely operate a machine.
• When working with other personnel on a work site, be sure
that all personnel know nature of work and understand all
hand signals that are to be used.
• Be sure that all guards and shields are installed in their
proper location. Have guards and shields repaired or
replaced immediately if damaged.
• Be sure that you understand the use and maintenance of
all safety features such as safety lock lever and seat belt.
Use them properly.
• Never remove, modify or disable any safety features.
Always keep them in good operating condition.
• Always check for and know the location of underground
and overhead utility lines before excavating.
• Failure to use and maintain safety features according to
instructions in this manual, Safety Manual and Shop
Manual can result in death or serious injury.
Know Your Machine
Know how to operate your machine. Know the purpose of all
controls, gauges, signals, indicators and monitor displays. Know
the rated load capacity, speed range, braking and steering
characteristics, turning radius and operating clearances. Keep in
mind that rain, snow, ice, loose gravel, soft ground, slopes etc.,
can change operating capabilities of your machine.
Proper Work Tools and Attachments
Only use work tools and attachments that are recommended by
DOOSAN for use on DOOSAN machines. When installing and
using optional attachments, read instruction manual for
attachment, and general information related to attachments in
this manual. Because DOOSAN cannot anticipate, identify or
test all attachments that owners may want to install on their
machines, contact DOOSAN for written authorization and

9. SP002322
Page 9
Track Excavator Maintenance Safety
approval of attachments, and their compatibility with optional
kits.
Attachments and attachment control systems that are
compatible with the machine are required for safe and reliable
machine operation. Do not exceed maximum operating weight
(machine weight plus attachment) that is listed on ROPS
certification plate.
Make sure that all guards and shields are in place on machine
and on work tool. Depending on type or combination of work
equipment, there is a potential that work equipment could
interfere with the cabin or other parts of machine. Before using
unfamiliar work equipment, check if there is any potential of
interference, and operate with caution.
While you are performing any maintenance, testing, or
adjustments to attachments, stay clear of the following areas:
cutting edges, pinch points, and crushing surfaces.
Never use attachment as a work platform or manlift.
Contact your DOOSAN distributor about auxiliary hydraulic kits
for attachments installation. If you are in doubt about
compatibility of a particular attachment with a machine, consult
your DOOSAN distributor.
Pressurized Fluids
Pressurized air or fluids can cause debris and/or fluids to be
blown out. This could result in death or serious injury.
Immediately after operations are stopped, coolant, engine oil,
and hydraulic oil are at their highest temperatures and the
radiator and hydraulic tank are still under pressure. Always wait
for temperature to cool down. Follow specified procedures when
attempting to remove caps, drain oil or coolant, or replacing
filters. Always wait for temperature to cool down, and follow
specified procedures when performing these operations. Failure
to do so can result in death or serious injury.
When pressurized air and/or pressurized water is used for cleaning,
wear protective clothing, protective shoes, and eye protection. Eye
protection includes goggles or a protective face shield.
Pressure can be trapped in a hydraulic system and must be
relieved before maintenance is started.
Releasing trapped pressure can cause sudden machine
movement or attachment movement. Use caution if you
disconnect hydraulic lines or fittings.
High-pressure oil that is released can cause a hose to whip or oil
to spray. Fluid penetration can result in death or serious injury. If
fluid enters skin or eyes, get immediate medical attention from a
physician familiar with this injury.
Obey all local laws and regulations for disposal of liquids.
To prevent hot coolant from spraying out, stop engine and wait for
coolant to cool. Using gloves, slowly loosen cap to relieve pressure.
FG018457
Figure 1

10. SP002551
Page 1
Track Assembly
SP002551
TRACK ASSEMBLY SP002551
Track
Assembly
Edition 1

11. SP002551
Page 5
Track Assembly
SAFETY INSTRUCTIONS
APPLICABLE MODELS
The contents of this section apply to the following models and
serial number ranges.
WARNING
AVOID DEATH OR SERIOUS INJURY
Instructions are necessary before operating or servicing
machine. Read and understand the Operation and
Maintenance Manual and signs (decals) on machine. Follow
warnings and instructions in the manuals when making
repairs, adjustments or servicing. Check for correct
function after adjustments repairs or service. Untrained
operators and failure to follow instructions can cause death
or serious injury.
MODEL SERIAL NUMBER RANGE
DX255LC-3 1001 and Up, 50001 and Up

12. SP002551Track Assembly
Page 6
GENERAL DESCRIPTION
The track assembly is composed of the following major
components:
1. Track
2. Front Idler Roller
3. Upper Roller
4. Lower Roller
5. Track Spring and Track Adjustment Cylinder

13. SP002551
Page 7
Track Assembly
TRACK TENSION
Track shoe link pins and bushings wear with normal usage,
reducing track tension. Periodic adjustment is necessary to
compensate for wear and it may also be required by working
conditions.
1. Track tension is checked by jacking up one side of the
excavator. See Figure 1. Place blocking under frame while
taking measurement.
Turn the track backward by 1 - 2 turns.
2. Measuring the distance (A, Figure 2) between the bottom
of the side frame and the top of the lowest crawler shoe.
Recommended tension for operation over most types of
terrain is distance "B" in below table.
NOTE: Clean off the tracks before checking clearance
for accurate measurements.
3. Too little sag in the crawler track (less than clearance
distance "B" in below table) can cause excessive
component wear. The recommended adjustment can also
be too tight causing accelerated stress and wear if ground
conditions are wet, marshy or muddy.
WARNING
AVOID DEATH OR SERIOUS INJURY
Measuring track tension requires two people. One person
must be in the operator's seat, operating the controls while
the other person makes dimensional checks. Block frame to
make sure the machine won't move or shift position during
service. Warm up the engine to prevent stalls, park the
excavator in an area that provides level, uniform ground
support and/or use support blocks when necessary.
The track adjusting mechanism is under very
high-pressure. NEVER release grease pressure too fast.
The track tension grease valve should never be loosened
more than one (1) complete turn from the fully tightened
down position. Bleed off grease pressure slowly. Keep your
body away from the valve always. Always wear eye and face
protection when adjusting track tension.
FG018383
90 ~ 110
Figure 1
A
FG000223
Figure 2

14. SP002551Track Assembly
Page 8
4. The increased clearance recommended for muddy, sandy
or snowy ground conditions is between distance "C" in the
below table.
5. Track tension adjustments are made through the grease
fitting (1, Figure 3) in the middle of each side frame. Adding
grease increases the length of an adjustment cylinder (2).
Extending the adjustment cylinder, increases the pressure
on the tension spring pushing the track idler wheel
outward.
6. If there is not enough slack or clearance in the tracks and
the adjustment is too tight, the idler wheel and adjusting
cylinder can be retracted by bleeding off grease through
hole in adjustment cylinder (2, Figure 3).
Terrain Type
Recommended
Distance "A"
Normal "B"
320 - 340 mm
(12.60 - 13.39 in)
Muddy, Sandy or Snowy "C"
340 - 370 mm
(13.39 - 14.57 in)
WARNING
AVOID DEATH OR SERIOUS INJURY
The track adjusting mechanism is under very high-
pressure. NEVER release grease pressure too fast.
The track tension grease valve should never be
loosened more than one (1) complete turn from the
fully tightened down position. Bleed off grease
pressure slowly. Keep your body away from the valve
always. Always wear eye and face protection when
adjusting track tension.
2
1
3
FG018365
Figure 3

15. SP002551
Page 9
Track Assembly
CLEANING AND INSPECTION
(WEAR LIMITS AND
TOLERANCES)
The tables that follow provide factory specified dimensional
limits (as new condition, recommended service and replacement
limit) for lower travel frame components.
Recommended maintenance to replace most listed components
requires welding on additional material and grinding off excess.
Some components must be replaced before the service limit is
exceeded. No maintenance or renewal is possible.
Compare the values in the tables with dimensions and profiles
shown in the adjacent figures.
CAUTION
AVOID INJURY
Refer to "Welding Precautions and Guidelines" information
in "General Maintenance Procedures" section for general
recommendations and specific safety precautions, before
starting any lower travel frame component rebuilding
procedure.

16. SP002551Track Assembly
Page 10
Track Shoe
8
9
2, 7
8
11
2, 7
FG025000
1
36
4 5
Figure 4

17. SP002551
Page 11
Track Assembly
No. Check Item Standard Dimension
Recommended Limit
for Maintenance
Limit for Use
(Repair - P or
Replace - R)
1 Link Pitch
190 mm
(7.48")
193 mm
(7.598")
194.5 mm [R]
(3.72")
2
Bushing Outside
Diameter
59 mm
(2.323")
57 mm
(2.244")
54.0 mm [R]
(2.126")
3 Link Height
105 mm
(4.134")
100 mm
(3.937")
96 mm [P]
(3.78")
4 Length at Tip
21 mm
(0.827")
5 Length at Tip
14 mm
(0.551")
6 Height
26 mm
(1.024")
20 mm
(0.787")
20 mm
(0.787")
7
Interference between
bushing and link
Standard
Dimension
(Bushing)
Tolerance
Standard
Dimension
(Link)
Tolerance
Standard
Interference
Repair
Limit
59 mm
(2.323")
+0.434
+0.394
59 mm
(2.323")
+0.074
0.0
0.32 -
0.434
8
Interference between
regular pin and link
Standard
Dimension
(Regular
Pin)
Tolerance
Standard
Dimension
(Link)
Tolerance
Standard
Interference
Repair
Limit
38 mm
(1.496")
+0.222
+0.162
37.8 mm
(1.488")
+0.062
0.0
0.3 - 0.422
9
Clearance between
regular pin and bushing
Standard
Dimension
(Regular
Pin)
Tolerance
Standard
Dimension
(Bushing)
Tolerance
Standard
Clearance
Repair
Limit
38 mm
(1.496")
+0.222
+0.162
38.85 mm
(1.530")
+0.500
0.0
-1.188 -
-0.628
10
Interference between
master pin and link
Standard
Dimension
(Master Pin)
Tolerance
Standard
Dimension
(Link)
Tolerance
Standard
Interference
Repair
Limit
37.8 mm
(1.488")
+0.280
+0.250
37.8 mm
(1.488")
+0.062
0.0
0.188 -
0.28
11
Clearance between
master pin and bushing
Standard
Dimension
(Master Pin)
Tolerance
Standard
Dimension
(Bushing)
Tolerance
Standard
Clearance
Repair
Limit
38 mm
(1.496")
-0.150
-0.350
38.85 mm
(1.530")
+0.500
0.0
-1.7 - -1.0

18. SP002551Track Assembly
Page 12
Lower Roller
3
2
1
4
FG024973
Figure 5
No. Check Item Standard Dimension
Recommended Limit for
Maintenance
Limit for Use
(Repair - P or
Replace - R)
1
OutsideDiameter
of Flange
195 mm
(7.677")
190 mm
(7.48")
185 mm [P]
(7.283")
2
OutsideDiameter
of Tread
160 mm
(6.299")
154 mm
(6.063")
150 mm [P]
(5.906")
3 Width of Tread
49 mm
(1.929")
55 mm
(2.165")
4 Width of Flange
29 mm
(1.142")
5
Clearance
between shaft
and bushing
Standard
Dimension
(Shaft)
Tolerance Standard
Dimension
(Bushing)
Tolerance
Standard
Clearance
Repair
LimitShaft Hole
70 mm
(2.756")
-0.06
-0.09
70.2 mm
(2.764")
+0.18
+0.13
-0.47 -
-0.39
68.3 mm (R)
(2.689")
6
Interference
between roller
and bushing
Standard
Dimension
(Roller)
Tolerance Standard
Dimension
(Bushing)
Tolerance
Standard
Interference
Repair
LimitRoller Hole
77 mm
(3.031")
+0.14 -
+0.09
77 mm
(3.031")
+0.03
-0.02
0.06 - 0.16

19. SP002551
Page 13
Track Assembly
Upper Roller
6
5
2
1
FG024974
4 3
Figure 6
No. Check Item Standard Dimension
Recommended Limit for
Maintenance
Limit for Use
(Repair - P or
Replace - R)
1
Outside Diameter of
Flange
169 mm
(6.654")
165 mm
(6.496")
2
Outside Diameter of
Tread
142 mm
(5.591")
136 mm
(5.354")
130 mm [P]
(5.118")
3 Width of Tread
51.5 mm
(2.028")
56.5 mm
(2.224")
4 Width of Flange
17 mm
(0.669")
5
Clearance between
shaft and bushing
Standard
Dimension
(Shaft)
Tolerance
Standard
Dimension
(Bushing)
Tolerance
Standard
Clearance
Repair
Limit
54.5 mm
(2.146")
0
-0.03
54.8 mm
(2.157")
+0.05
0
-0.38 - -0.3
6
Interference between
roller and bushing
Standard
Dimension
(Roller)
Tolerance
Standard
Dimension
(Bushing)
Tolerance
Standard
Interference
Repair
Limit
61 mm
(2.402")
+0.15 -
+0.1
61 mm
(2.402")
+0.04
-0.03
0.06 - 0.18

20. SP002551Track Assembly
Page 14
Front Idler
4
3 5
7
6
1
2
FG024975
Figure 7
No. Check Item Standard Dimension
Recommended Limit for
Maintenance
Limit for Use
(Repair - P or
Replace - R)
1
Outside Diameter of
Flange
541.6 mm
(21.323")
2
Outside Diameter of
Tread
500 mm
(19.685")
492 mm
(19.370")
488 mm [P]
(19.213")
3 Width of Protrusion
85 mm
(3.346")
4 Total Width
160 mm
(6.299")
5 Width of Tread
37.5 mm
(1.476")
35 mm
(1.378")
33 mm
(1.299")
6
Clearance between
shaft and bushing
Standard
Dimension
(Shaft)
Tolerance
Standard
Dimension
(Bushing)
Tolerance
Standard
Clearance
Repair
Limit
75 mm
(2.953")
0
-0.03
75 mm
(2.953")
+0.415
+0.37
-0.445 -
-0.37
7
Interference between
idler and bushing
Standard
Dimension
(Idler)
Tolerance
Standard
Dimension
(Bushing)
Tolerance
Standard
Interference
Repair
Limit
85 mm
(3.346")
+0.12
+0.09
85 mm
(3.346")
+0.035 -
0
0.055 -
0.12

21. SP002551
Page 15
Track Assembly
TRACK SHOES AND LINKS
Track Removal
1. Position machine on a smooth level surface with adequate
room for forward and reverse travel.
2. Release track tension. Refer to “Track Tension” on page -7
in this section for procedure.
3. Move machine until master link (4, Figure 9) is positioned
at approximately 4 o'clock from top position on front idle
roller.
4. Put a wooden block under track shoes, as shown.
5. Loosen grease valve (1, Figure 10) for track adjuster to
drain grease out. Use socket wrench 27 mm
6. Remove four nuts and bolts (1 and 2, Figure 9) holding
shoe to link. Remove enough shoes to make access to
master pin.
7. Remove master pin from master link by hammer or press.
Remove pin after detaching shoe.
FG019247
Figure 8
Figure 9
1
2
4
FG004355
Figure 10
1
FG004356
WARNING
AVOID DEATH OR SERIOUS INJURY
The track adjusting mechanism is under very high-
pressure. NEVER release grease pressure too fast.
The track tension grease valve should never be
loosened more than one (1) complete turn from the
fully tightened down position. Bleed off grease
pressure slowly. Keep your body away from the valve
always. Always wear eye and face protection when
adjusting track tension.

22. SP002551Track Assembly
Page 16
8. Move unit forward until entire track is laying on ground.
NOTE: Do not drive unit off track.
9. Rotate upper structure to 90° from track. Use bucket and
boom to raise track frame off track.
10. Position blocking under frame.
Track Installation
1. Lay rebuilt or new track into position under track frame.
End of track must be positioned under drive sprocket.
2. With upper structure at 90° to track frame. Use bucket and
boom to raise track frame off blocking.
3. With blocking removed, lower track frame onto track. Make
sure all rollers are properly positioned on track.
4. Move unit forward while feeding track up over drive
sprocket. Continue to pull track back until it engages front
idle roller.
5. Align master links and install master pin.
6. Install four nuts and bolts (to fix track shoe).
7. Apply track tension. Refer to “Track Tension” on page -7"
in this section for procedure.
FG003911
Figure 11
FG018383
90 ~ 110
Figure 12
Figure 13
FG018383
90 ~ 110
FG003912
Figure 14

23. SP002551
Page 17
Track Assembly
FRONT IDLER ROLLER
Parts List
1
FG022507
8
6
5
7
3
4
2
9
9
5
7
8
3
6
Figure 15
Reference
Number
Description
1 Idler Assembly
2 Idler
3 Bearing
4 Shaft
5 Bushing
6 Pin
7 Floating Seal
8 O-ring
9 Plug
Reference
Number
Description

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25. SP002551Track Assembly
Page 18
Front Idler Roller Disassembly
1. Remove plug (9, Figure 16) from idler assembly (1), and
drain oil into a suitable container.
2. Separate the pin (6, Figure 17) from the bearing (3).
3. Use a press to remove bearing from the axle (4). Separate
the O-ring (8, Figure 18) from the axle.
4. Detach the floating seal (7, Figure 19) from the idler (2)
and bearing (3).
9
FG022246
Figure 16
FG022247
6
3
Figure 17
3
FG022507
4
8
Figure 18
3
7
2
7
3
FG022508
Figure 19

26. SP002551
Page 19
Track Assembly
5. Use a press to separate the axle (4, Figure 20), O-ring (8)
and bearing (3).
6. Remove bushing (5, Figure 21) with the press and special
tool (10, ST-1909).
FG022509
4
3
8
Figure 20
FG022510
10 5 2
Figure 21

27. SP002551Track Assembly
Page 20
Front Idler Roller Reassembly
1. Degrease, clean and dry all parts before reassembly.
Insert bushing (5, Figure 21) into the idler (2).
2. Grease O-ring (8, Figure 22) and insert it into the axle.
3. Align the bearing (3, Figure 22) and axle (4) holes and pin
(6) them together.
4. Install floating seal (7, Figure 23) inside the idler (2) and
bearing (3).
NOTE: Apply clean gear oil (ISO VG 220EP) to the joint
side of the floating seal. Apply grease to the
floating seal O-ring.
5. Install idler (2, Figure 24) on the axle.
6. Install bearing (3, Figure 24) and pin (6) to the axle.
NOTE: Fill the idler assembly with new gear oil (ISO VG
220EP) with approximately 320 cc (10.8 oz).
7. Install plug (9, Figure 24) on the bearing.
FG022511
4
3
8
8
6
Figure 22
Figure 23
3
7
2
7
3
FG022508
FG022253
6
3
9
2
Figure 24