This document provides service instructions for disassembling and assembling the mast on various Mitsubishi lift truck models. It includes specifications for lift cylinders, hydraulic components, and safety procedures. The document is organized by system and provides diagrams, part lists, and step-by-step instructions for disassembling components like lift cylinders, hoses, and brackets. Cautions are provided regarding weights, pressures, and ensuring safety during repair work.

1. Service Manual
SENB8470
M70, M80, M100, M120
Mast Disassembly & Assembly
M70D A1EC4-60001-79999
A1EC4-80001-99999
M80D A1EC4-60001-79999
A1EC4-80001-99999
M100D A1EC4-60001-79999
A1EC5-80001-99999
M120D A1EC5-60001-79999
A1EC5-80001-99999

2. FOREWORD
The instructions are grouped by systems to serve the convenience of your ready
reference.
Long productive life of your lift trucks depends to a great extent on correct
servicing — the servicing consistent with what you will learn from this service
manual. We hope you read the respective sections of this manual carefully and
know all the components you will work on before attempting to start a test, repair
or rebuild job.
The descriptions, illustrations and specifications contained in this manual were of
the trucks of serial numbers in effect at the time it was approved for printing.
Caterpillar reserves the right to change specifications or design without notice
and without incurring obligation.
SAFETY RELATED SIGNS
The following safety related signs are used in this
service manual to emphasize important and
critical instructions:
WARNING Indicates a specific potential
hazard resulting in serious
bodily injury or death.
CAUTION Indicates a specific potential
hazard resulting in bodily
injury, or damage to, or
destruction of the machine.
NOTE Indicates a condition that can
cause damage to, or shorten
service life of the machine.
Pub. No. SENB8470

3. The proper and safe lubrication and
maintenance for this lift truck,
recommended by Mitsubishi, are
outlined in the OPERATION &
MAINTENANCE MANUAL for these
trucks.
Improper performance of lubrication
or maintenance procedures is
dangerous and could result in injury
or death. Read and understand the
OPERATION & MAINTENANCE
MANUAL before performing any
lubrication or maintenance.
WARNING
WARNING
SAFETY
The serviceman or mechanic may be unfamiliar with
many of the systems on this truck. This makes it
important to use caution when performing service
work. A knowledge of the system and/or compo-
nents is important before the removal or disassem-
bly of any component.
Because of the size of some of the truck compo-
nents, the serviceman or mechanic should check the
weights noted in this Manual. Use proper lifting pro-
cedures when removing any components.
Following is a list of basic precautions that should
always be observed.
1. Read and understand all warning plates and
decals on the truck before operating, lubricating
or repairing the product.
2. Always wear productive glasses and protective
shoes when working around trucks. In particu-
lar, wear protective glasses when pounding on
any part of the truck or its attachments with a
hammer or sledge. Use welders gloves,
hood/goggles, apron and other protective cloth-
ing appropriate to the welding job being per-
formed. Do not wear loose-fitting or torn cloth-
ing. Remove all rings from fingers when work-
ing on machinery.
3. Do not work on any truck that is supported only
by lift jacks or a hoist. Always use blocks or
jack stands to support the truck before perform-
ing any disassembly.
Do not operate this truck unless you
have read and understand the
instructions in the OPERATION &
MAINTENANCE MANUAL. Improper
truck operation is dangerous and
could result in injury or death.
WARNING
4. Lower the forks or other implements to the
ground before performing any work on the
truck. If this cannot be done, make sure the
forks or other implements are blocked correctly
to prevent them from dropping unexpectedly.
5. Use steps and grab handles (if applicable) when
mounting or dismounting a truck. Clean any
mud or debris from steps, walkways or work
platforms before using. Always face truck when
using steps, ladders and walkways. When it is
not possible to use the designed access system,
provide ladders, scaffolds, or work platforms to
perform safe repair operations.
6. To avoid back injury, use a hoist when lifting
components which weighs 23 kg (50 lb.) or
more. Make sure all chains, hooks, slings, etc.,
are in good condition and are of the correct
capacity. Be sure hooks are positioned correct-
ly. Lifting eyes are not to be side loaded during
a lifting operation.
7. To avoid burns, be alert for hot parts on trucks
which have just been stopped and hot fluids in
lines, tubes and compartments.
8. Be careful when removing cover plates.
Gradually back off the last two bolts or nuts
located at opposite ends of the cover or device
and pry cover loose to relieve any spring or
other pressure, before removing the last two
bolts or nuts completely.
9. Be careful when removing filler caps, breathers
and plugs on the truck. Hold a rag over the cap
or plug to prevent being sprayed or splashed by
liquid under pressure. The danger is even
greater if the truck has just been stopped
because fluids can be hot.

4. 10. Always use tools that are in good condition and
be sure you understand how to use them before
performing any service work.
11. Reinstall all fasteners with same part number.
Do not use lesser quality fastener if
replacements are necessary. Do not mix metric
fastener with standard nuts and bolts.
12. If possible, make all repairs with the truck
parked on a level, hard surface. Block truck so
it does not roll while working on or under truck.
13. Disconnect battery and discharge any
capacitors (electric trucks) before starting to
work on truck. Hang “Do not Operate” tag in
the Operator’s Compartment.
14. Repairs, which require welding, should be
performed only with the benefit of the
appropriate reference information and by
personnel adequately trained and
knowledgeable in welding procedures.
Determine type of metal being welded and
select correct welding procedure and
electrodes, rods or wire to provide a weld metal
strength equivalent at least to that of parent
metal.
15. Do not damage wiring during removal
operation. Reinstall the wiring so it is not
damaged nor it will be damaged in operation by
contacting sharp corners, or by rubbing against
some object or hot surface. Do not connect
wiring to a line containing fluid.
16. Be sure all protective devices including guards
and shields are properly installed and
functioning correctly before starting a repair. If
a guard or shield must be removed to perform
the repair work, use extra caution.
17. Always support the mast and carriage to keep
carriage or attachments raised when
maintenance or repair work is performed,
which requires the mast in the raised position.
18. Loose or damaged fuel, lubricant and hydraulic
lines, tubes and hoses can cause fires. Do not
bend or strike high pressure lines or install ones
which have been bent or damaged. Inspect
lines, tubes and hoses carefully. Do not check
for leaks with your hands. Pin hole (very small)
leaks can result in a high velocity oil stream
that will be invisible close to the hose. This oil
can penetrate the skin and cause personal injury.
Use cardboard or paper to locate pin hole leaks.
19. Tighten connections to the correct torque. Make
sure that all heat shields, clamps and guards are
installed correctly to avoid excessive heat,
vibrations or rubbing against other parts during
operation. Shields that protect against oil spray
onto hot exhaust components in event of a line,
tube or seal failure, must be installed correctly.
20. Relieve all pressure in air, oil or water systems
before any lines, fittings or related items are
disconnected or removed. Always make sure all
raised components are blocked correctly and be
alert for possible pressure when disconnecting
any device from a system that utilizes pressure.
21. Do not operate a truck if any rotating part is
damaged or contacts any other part during
operation. Any high speed rotating component
that has been damaged or altered should be
checked for balance before reusing.

5. Unit: mm (in.)
Clearance A
0.020 to 0.105
between (0.00079 to 0.00413)
cylinder and
B
0.15
piston (0.0059)
A: Assembly standard
B: Repair or service limit
HOW TO READ THIS MANUAL
Disassembly diagram (example)
Each disassembly diagram is followed
by Disassembly sequence and
Suggestions disassembly.
Disassembly sequence
1 Cover, Bolt, Washer (part name)
2 Output shaft (part name)
Suggestion for disassembly
(1) Output shaft removal
1
2
3
4
v
v
v
Symbols or abbreviations
OP..........................Option
R1/4 ......................Taper pipe thread (external) 1/4 inch (formerly PT1/4)
Rc1/8 ....................Taper pipe thread (internal) 1/8 inch (formerly PT1/8)
G1/4A....................Straight pipe thread (external) 1/4 inch (formerly PF1/4-A)
Rp1/8 ....................Straight pipe thread (internal) 1/8 inch (formerly PS1/8)

6. HYDRAULIC SYSTEM
1-1
Specifications
Truck Models
M70D M100D
M80D M120D
Items
Flow regulator
Type Adjustable Adjustable
valve Control flow capacity
100 (26.42) 115 (30.38)
liter/min (U.S.gal/min)
Simplex mast Internal diameter mm (in.) 60 (2.36) 70 (2.75)
Lift cylinders Stroke mm (in.) 1650 (65) 1650 (65)
Duplex mast Internal diameter mm (in.) 90 (3.54) 110 (4.33)
First lift cylinders Stroke mm (in.) 820 (32.28) 845 (33.27)
Duplex mast Internal diameter mm (in.) 55 (2.17) 60 (2.36)
Second lift cylinders Stroke mm (in.) 1590 (62.60) 1585 (62.40)
Triplex mast Internal diameter mm (in.) 90 (3.54) 110 (4.33)
First lift cylinders Stroke mm (in.) 820 (32.28) 845 (33.27)
Triplex mast Internal diameter mm (in.) 60 (2.36) 70 (2.75)
Second lift cylinders Stroke mm (in.) 1480 (58.27) 1530 (60.24)
Hydraulicsystem

7. HYDRAULIC SYSTEM
1-2
Lift Cylinders
2
1
•• ••••••
•
•• • • • •
•
*
6
*
7 4
*
8
*
91011
3
*
5
206951
2
1
*
6
*
7
4
*
8
*
109 11 121335
202976
Simplex Mast
Lift Cylinders (G40A)
Parts marked with * are included in the seal kit.
1 Cylinder tube
2 Piston rod
3 Cylinder head
4 Bushing
5 U-ring
6 Wiper ring
7 O-ring
8 U-ring
Simplex Mast
9 Backup ring
10 Bushing
11 Spacer
1 Cylinder tube
2 Piston rod
3 Cylinder head
4 Bushing
5 Holder
6 U-ring
7 Wiper ring
8 O-ring
9 Piston ring
10 U-ring assembly
11 U-ring holder
12 Stopper
13 Spacer
Lift Cylinders
(G45A, G55A
Parts marked with * are included in the seal kit.

8. HYDRAULIC SYSTEM
1-3
2 1
*
6
*
7
*
13, 144
*
8
*
9
*
10 11 123
•
• •
•
•
•
• •
•
*
5
206950Parts marked with * are included in the seal kit.
Duplex Mast
First Lift Cylinder (H40A)
1 Cylinder tube
2 Piston rod
3 Cylinder head
4 Bushing
5 U-ring
6 Wiper ring
7 O-ring
8 O-ring
9 Seal ring assembly
10 Slide ring
11 Check valve
12 Snap ring
13 Plug
14 Gasket
Triplex Mast
First Lift Cylinders (J40A thru J70A)

9. HYDRAULIC SYSTEM
1-4
21
*
6
*
7 5 4 1617 151011 1312143 18
*
8
*
9
206949
2 1
*
9
*
8
*
7
*
6
*
5 114 123 10
207778A
Duplex Mast
Second Lift Cylinders (H40A)
1 Cylinder tube
2 Piston rod
3 Cylinder head
4 Bushing
5 Holder
6 U-ring
7 Backup ring
8 Wiper ring
9 O-ring
10 Piston
11 Slide ring
12 Set screw
13 Check valve
14 Cushion spool
15 Spring
16 Snap ring
17 Steel ball
18 Set screw
Parts marked with * are included in the seal kit.
Parts marked with * are included in the seal kit.
Triplex Mast
Second Lift Cylinders (J40A)
1 Cylinder tube
2 Piston rod
3 Cylinder head
4 Bushing
5 U-ring
6 Wiper ring
7 O-ring
8 U-ring
9 Backup ring
10 Bushing
11 Spring guide
12 Spring
13 Cushion spool
14 Pin
15 Snap ring
16 Spacer
•
•
•
•
•
•
• •
•••
•
•
15 14 1316

10. HYDRAULIC SYSTEM
1-5
2 167 5 4 1617 1510 1113 12143 8 9
207779A
Triplex Mast
Second Lift Cylinders (J45A, J55A)
1 Cylinder tube
2 Piston rod
3 Cylinder head
4 Bushing
5 Holder
6 U-ring
7 Wiper ring
8 O-ring
9 Piston ring
10 U-ring assembly
11 Holder
12 Stopper
13 Spring guide
14 Spring
15 Cushion rod
16 Spring pin
17 Spacer
Parts marked with * are included in the seal kit.

11. HYDRAULIC SYSTEM
1-6
6 4 1253
202978
Flow Regulator Valve
1 Set bolt, Lock nut
2 Sleeve, O-ring
3 Piston, Spring pin, Washer spring, Valve
4 Spring
5 Spring guide, O-ring
6 Valve body
M80D thru M120D
•
•
• •

12. HYDRAULIC SYSTEM
1-7
41 23
204626
Down Safety Valve
1 Connector
2 Valve
3 Spring
4 Spring pin
The down safety valve is located at the bottom
side of right-hand lift cylinder.
This valve provides a means of preventing the
load from lowering, unsafely, rapidly, when a
hose bursts.
Cut-off flow rate
Simplex G40A G45A, G55A
Duplex H40A —
Triplex J40A J45A, J55A
Cut-off flow rate 90 120 0
liter (U.S.gal)/min (23.8 ) (31.7 )
Cut-off flow rate Stamped number
Free flow Regulated flow
Mast
model
–0
–15
–0
–4
+5
–10
+1.3
–2.6
Do not reuse down safety valve
after a lift line hose failure.
WARNING

13. HYDRAULIC SYSTEM
1-8
207784
Lift Cylinders
Dual-stage Panoramic Mast (Simplex Mast)
Sequence
1 Nuts
2 Fork, Lift bracket
3 Return (low-pressure)
hose
4 Hose guard
5 High-pressure hose
6 Set bolt, Shims
Suggestions
1. Lift bracket removal
(1) Tilt the mast forward, and lower the inner mast
to the bottom. Slacken the lift chains, and
remove the nuts from the anchor bolts.
(2) Tilt the mast back to vertical position. Raise
the inner mast until the lift bracket becomes
free. Then, back the truck away from the lift
bracket and fork assembly.
7 Cylinder clamp, Cushion,
Collar, Shims
8 Lift cylinder, Bracket
1
2
3
7
8
4
5
6
204873A
8

14. 1-9
HYDRAULIC SYSTEM
206691
202983
Right cylinder Left cylinder
4. Removing set bolts
(1) Remove the set bolt at the top of each lift
cylinder. Lift the inner mast to separate the
cylinder rod ends. To lift the inner mast, hitch
a sling around the mast with protective rag.
NOTE
The rod end of either lift cylinder is shim
adjusted to eliminate the difference in stroke
between the cylinders. Before removing the
set bolts, make a record of the amount of
shims and cylinders to which the shims are
fitted.
(2) Tie wood blocks under the inner mast and
detach the sling. Make sure the right and left
wood blocks are the same in height.
3. Disconnecting high-pressure hoses
Slowly push the lift lever forward to lower the
lift bracket to the ground. Disconnect the high-
pressure hoses at the joints indicated by
arrows. Use a container to catch oil flowing
out of the hoses.
206965
To hydraulic tank
2. Removing return hose
Lift the mast to the maximum lift position, and
turn the key switch off. Disconnect the return
hose from the right and left lift cylinders at the
connectors.
206967

15. HYDRAULIC SYSTEM
1-10
206968
5. Removing lift cylinders
Hitch a sling to the lift cylinder from the rear
side of the mast, and remove the cylinder.
Hitch the sling before removing the cylinder
clamp.
Installation
To install, follow the reverse of removal
sequence, and do the following steps once com-
pleted:
1. Extend and retract the lift cylinders several
times under no load condition to bleed air out
of the cylinder circuits and to make sure that
the cylinders move smoothly.
2. Check the oil level in the hydraulic tank with
an oil level gauge. (Make reference to
Hydraulic Tank section.)
3. Check to make sure that the lift height is
correct.
4. After the lift cylinders or piston rods have
been replaced, check for difference in stroke
between the two cylinders. (Make reference
to Group 11 MAST AND FORKS.)

16. 1-11
HYDRAULIC SYSTEM
Lift Cylinders
The following describes the procedures for removing and installing the mast assembly. Note that the
triple-stage full free panoramic mast (Triplex Mast) is used as an example.
Triple-stage Full Free Panoramic Mast (Duplex and Triplex Masts)
Sequence
1 Nuts
2 Lift bracket assembly
3 First lift cylinder
4 Chain wheel support assembly
5 Second lift cylinders
Suggestions
1. Removing lift bracket assembly 2
(1) Lower lift bracket assembly 2, and place wood
blocks under the assembly. Tilt the mast
forward, lower the inner mast to the bottom,
then remove nuts 1 from the anchor bolts of
the first lift chains. 207786
207785
2
4
5
1
3
1

17. HYDRAULIC SYSTEM
1-12
(2) Position the mast upright. Raise the inner mast
until main rollers 6 of lift bracket assembly 2
become free. Then, slowly move the vehicle in
reverse to separate from lift bracket 2.
2. Removing first lift cylinder 3
(1) Hitch a sling to first lift cylinder 3, and
suspend the cylinder with a crane. Wind the
sling securely to prevent slipping.
(2) Remove the lift cylinder connecting and
mounting bolts, and gently dismount first lift
cylinder 3.
3. Removing second lift cylinders 5
(1) Disconnect hoses from second lift cylinders 5.
(2) Remove stopper bolts at the upper sections of
second lift cylinders 5, and lift the inner mast
[dual-stage full free panoramic mast] or
middle mast [triple-stage full free panoramic
mast] approximately 550 mm (21.67 in.) using
slings.
201735
207787
207788
5
3
6
2

18. 1-13
HYDRAULIC SYSTEM
(3) Place wood blocks under the inner mast [dual-
stage full free panoramic mast] or middle mast
[triple-stage full free panoramic mast].
Make sure the right and left wood blocks are
the same in height.
(4) Hitch a sling to second lift cylinder 5 behind
the mast, remove cylinder clamp retaining
bolts, and gently remove second lift cylinder
5.
Wind the sling securely to the cylinder. The
cylinder cannot be lifted straight up since the
mast cross-member is located above the
cylinder. Tilt the cylinder and move it away
from the cross-member to remove. Be careful
not have the hands caught between the
cylinder and mast.
Installation
To reinstall, follow the removal sequence in
reverse, and service as follows.
(1) Install chain wheel support assembly 4 parallel
to a line connecting the centers of chain
anchor bolt holes on first lift cylinder 3 to
prevent chains from twisting.
(2) Adjust the chain tensions.
(See the section Inspection and Adjustment.)
(3) Extend and retract the lift cylinders several
times under no load condition to bleed air out
of the cylinder circuits and to make sure that
the cylinders move smoothly.
(4) After proper operation is confirmed, check the
oil level.
Good Bad
202983
207789
207638
5

19. HYDRAULIC SYSTEM
1-14
206970
1
•
4
2
3
206971
Tilt Cylinders
1 Tilt cylinder pin
2 Hoses
3 Tilt cylinder pin
4 Tilt cylinder
Start by:
(1) Lower the forks to the bottom, and tilt the
mast fully forward.
(2) Hitch a sling to the top crossmember of outer
mast, and support the weight of the mast with
a hoist.
Suggestions
1. Retracting piston rod
Remove tilt cylinder pin 1. Start the engine
and retract the piston rod to the full stroke,
then stop the engine.
2. Disconnecting hoses
Disconnect hoses 2 from the cylinder at the
connectors. Use a container to catch oil from
flowing out of the cylinder. Attach caps to the
connectors of the cylinder to protect the
threads of the connectors and to prevent oil
from flowing out of the cylinder when the
cylinder is removed.

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