Ingersoll-Rand 3940 Series, 3942 Series, 3955 Series Maintenance Information

10569408

Edition 1

January 2006

Air Impact Wrench

Series 3940, 3942 & 3955

Maintenance Information

Save These Instructions

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WARNING

Always wear eye protection when operating or performing maintenance on this tool.
Always turn off the air supply and disconnect the air supply hose before installing, removing or adjusting any accessory on this tool, or before
performing any maintenance on this tool.

Note: When reading the instructions, refer to exploded diagrams in Parts Information Manuals when applicable (see under Related Documentation for form

numbers).

Lubrication

Each time a Series 3940, 3942 or 3955 Impactool is disassembled for
maintenance and repair or replacement of parts, lubricate the tool as
follows:

1. Work approximately 12 to 15 cc of Ingersoll-Rand No. 170 Grease
into the impact mechanism. Coat the Anvil (38) lightly with grease.

Also, coat the inside of the Hammer Case Bushing (40) with grease.
Inject approximately 2 to 4 cc of grease into the Grease Fitting (2).

2. Use Ingersoll-Rand No. 10 Oil for lubricating the motor. Inject
approximately 1 to 2 cc of oil into the Straight Inlet (10) before
attaching the air hose.

Disassembly
General Instructions

1. Do not disassemble the tool any further than necessary to replace or
repair damaged parts.

2. Whenever grasping a tool or a part in a vise, always use leather­covered or copper-covered vise jaws to protect the surface of the
part and help prevent distortion. This is particularly true of threaded
members and housings.

3. Do not remove any part which is a press fit in or on a subassembly
unless the removal of that part is necessary for repairs or
replacement.

4. Do not disassemble the tool unless you have a complete set of new
gaskets and O-rings for replacement.

Disassembly of the Impactool

1. Grasp tool in copper-covered or leather-covered vise jaws with
square drive upward.

2. Squeeze sides of the Exhaust Deflector (32) and remove from Motor
Housing Assembly (26). Remove the Exhaust Silencer (33).

3. Using a hex wrench, unscrew and remove the four Hammer Case
Cap Screws (41) and remove Dead Handle Bracket (42).

4. While lightly tapping on the end of Anvil (38) with a plastic hammer,
lift off Hammer Case (39).

5. Remove the Hammer Case Gasket (34).

6. Remove Anvil by rotating it as it is lifted out of the assembly.

7. Lift remaining hammer assembly off rotor shaft.

8. Push two Hammer Pins (36) out of the Hammer Frame
Assembly (35) and slide two Hammers (37) out of the Frame.

Disassembly of the Impact Mechanism

1. Set mechanism, driver end up, on a workbench.

NOTICE

Note the twin hammers within the Hammer Frame.
These are identical, but must be placed in the Hammer
Frame in a certain relationship. Using a felt-tipped pen,
mark the top hammer “T↑” and the bottom hammer
“B↑” with the arrows pointing upward. Mark both
Hammers on the same end.

2. With mechanism sitting upright on a workbench, slowly rotate Anvil in
a clockwise direction until it comes up solid.

NOTICE

If you continue to rotate the Anvil, it will cam the
Hammers out of engagement. Do not allow this to
happen; merely rotate the Anvil until it comes up solid.

3. Hold Hammer Frame firmly and, without disturbing hammers, gently
lift Anvil, simultaneously rotating it clockwise about 1/8 of a turn, from
the Hammer Frame.

NOTICE

The twin hammers will be free to slide from the Hammer
Frame when the Hammer Pins are removed. Do not drop
the Hammers.

4. With Anvil removed, lift out the two Hammer Pins.

5. Remove the Hammers.

Disassembly of the Reverse Valve

1. Lightly clamp Motor Housing Assembly (26) in leather-covered or
copper-covered vise jaws with Handle Assembly (1) upward.

NOTICE

Excessive clamping pressure will distort the Motor
Housing and make motor removal extremely difficult. Do
not insert the hammer case end of the Motor Housing
more than 1” (25 mm) into the vise jaws.

2. Using a hex wrench, unscrew and remove the four Handle Cap
Screws (15). Lift assembled handle and Handle Gasket (17) off
Motor Housing and set them aside.

3. Lift Motor Clamp Washer(s) (16) off Housing.

4. Move Reverse Lever (12) to center position and using a drift pin to
push from below, grasp Lever and lift Reverse Valve Assembly (13)
out of Housing.

NOTICE

Make certain the Lever is in the center position to avoid
jamming the Reverse Lock Plunger (30) when the
Reverse Valve Assembly is removed.

5. Pull Lever off Reverse Valve and remove Reverse Valve Bushing
Seal (14) from groove on Valve.

6. Using needle nose pliers, remove Reverse Lock Plunger and
Reverse Lock Plunger Spring (31) from Motor Housing.

Disassembly of the Motor

1. Remove assembled motor and Motor Housing from vise jaws and
using a plastic hammer, tap splined shaft of Rotor (22) to dislodge
Rotor from Front Rotor Bearing (25).

2. Lift Motor Housing (26) off Rotor, Rear End Plate (20) and Rear Rotor
Bearing (18) which will remain together as a unit.

3. Remove Vanes (23) from Rotor.

4. Pull Rear End Plate off Rotor.

5. Open a set of vise jaws wide enough to clear hub of Rear End Plate
and sharply rap hub end of end plate on top of jaws to dislodge Rear
Rotor Bearing.

6. Remove Cylinder Dowel (19).

7. For 3940 and 3942 Series: To remove Cylinder (21) and Front End
Plate (24), thread four 1/4”-20 thread socket head cap screws that
are at least 3” (75 mm) long into handle end of Housing. Grasping
Housing with installed screws downward, sharply strike heads of
screws on a sturdy table to dislodge Cylinder. Cylinder should drop
out of Housing after a few impacts. If it does not, proceed as follows:
For 3955 Series: To remove Cylinder (21) and Front End Plate (24),
thread four 5/16”-18 thread socket head cap screws that are at least
3” (75 mm) long into handle end of Housing. Grasping Housing with
installed screws downward, sharply strike heads of screws on a
sturdy table to dislodge Cylinder. Cylinder should drop out of Housing
after a few impacts. If it does not, proceed as follows:

10569408_ed1 3

WARNING

The following procedure requires the use of heat. Take
all necessary precautions to prevent burns. Carefully
heat alternate sides of Housing until it is very warm.
Using thick, heavy gloves to avoid being burned, grasp
Housing and repeat attempt to dislodge Cylinder.

8. Open a set of vise jaws wide enough to clear hub of Front End Plate
and sharply rap hub end of end plate on top of jaws to dislodge Front
Rotor Bearing.

9. Remove two Air Port Gaskets (29) and Air Port Gasket
Retainers (28) from Housing.

Disassembly of the Handle

1. Clamp Trigger Handle Assembly in leather-covered or copper­covered vise jaws with the Straight Inlet (10) upward.

2. Using a wrench, unscrew and remove Inlet as well as Air Strainer
Screen (9) and valve Spring (8).

3. Remove Throttle Valve Assembly (6) and Valve Plunger (5) from
Handle.

4. If Trigger (3) must be removed, use an arbor press to push Trigger
Pin (4) from the Handle and slide Trigger out of slot in Handle.

Assembly
General Instructions

1. Always press on the inner ring of a ball-type bearing when installing
the bearing on a shaft.

2. Always press on the outer ring of a ball-type bearing when installing
the bearing into a bearing recess.

3. Whenever grasping a tool or part in a vise, always use leather­covered or copper-covered vise jaws. Take extra care with threaded
members and housings.

4. Always clean every part and wipe every part with a thin film of oil
before installation.

5. Apply a film of O-ring lubricant to all O-rings before final assembly.

Assembly of the Handle

1. Position Trigger (3) in Handle (1) and using an arbor press, push
Trigger Pin (4) full length into Handle so that it captures Trigger.

2. Clamp Handle in leather-covered or copper-covered vise jaws with
air inlet opening upward.

3. Coat Throttle Valve Plunger (5) with oil and insert it, rounded end
leading, into the inlet hole in Handle.

4. Install a new Throttle Valve Seal (7) on Throttle Valve (6) and insert
assembly, Valve Seal leading, into inlet hole in Handle.

5. Encircle cone end of Air Strainer Screen (9) with large end of Throttle
Valve Spring (8) and insert both parts, Spring leading, into the inlet
hole in Handle.

6. Install Straight Inlet (10) over Strainer Screen in Handle and tighten
Inlet between 50 and 60 ft-lb (68 and 81 Nm) torque.

7. Remove Handle from vise and test Trigger. If Trigger functions
properly, place assembled Handle aside. If it does not function
properly, disassemble Handle to determine cause of problem.

Assembly of the Motor

1. Lightly clamp Motor Housing (26) in leather-covered or copper­covered vise jaws with handle end upward.

NOTICE

Excessive clamping pressure will distort the Motor
Housing and make motor installation extremely difficult.
Do not insert the hammer case end of the Motor
Housing more than 1” (25 mm) into the vise jaws.

2. Grease Front Rotor Bearing (25) and install it in recess of Front End
Plate.

3. Coat inside surface of Housing and outer edge of
Front End Plate (24) with a light film of oil.

4. Using a long tee hex wrench as an alignment pin, insert Front End
Plate, copper face trailing, into Motor Housing. Align dowel hole in
End Plate with dowel hole at the bottom of motor bore.

5. Lubricate and insert a new fiber Air Port Gasket Retainer (28) in one
of the air ports inside Motor Housing.

6. Install an Air Port Gasket (29) in the air port against Gasket Retainer
with flat end of Gasket away from Retainer.

7. Repeat Steps 5 and 6 to install remaining Gasket and Retainer in the
other air port.

8. Coat outside of Cylinder (21) with a light film of oil and using long tee
hex wrench as an alignment pin to align the holes in Cylinder with
holes in Front End Plate and Housing, insert Cylinder into Housing.

9. Coat inside of Cylinder and Rotor (22) with a light film of oil and insert
the splined hub of Rotor through Cylinder into Front End Plate.

10. Coat each Vane (23) with a light film of oil and insert a Vane into each
slot in the Rotor. Vanes must be installed with curved edge toward
center of Rotor. Spin the Rotor to settle Vanes in position.

11. Using long tee hex wrench to align hole in Rear End Plate (20) with
hole in Cylinder, insert the Rear End Plate, bronze face leading, into
Motor Housing against the Cylinder. End Plate is properly seated
when large trailing face of End Plate is slightly below face of Motor
Housing.

12. Grease Rear Rotor Bearing (18) and install it in recess of Rear End
Plate.

13. Remove alignment pin from assembled motor and install Cylinder
Dowel (19). The Dowel is properly seated when end of Dowel does
not protrude above End Plate.

14. Install Motor Clamp Washer(s) (16) against Rear End Plate so that
large outer edge of Washer contacts End Plate.

Assembly of the Reverse Valve

1. Inject a small amount of grease into hole in Motor Housing (26)
where Reverse Lock Plunger (30) will be installed. With grease to
hold them in position, install Reverse Lock Plunger Spring (31) and
Lock Plunger.

2. Install a new Reverse Valve Bushing Seal (14) in annular groove on
Reverse Valve (13).

3. Coat Reverse Valve with a light film of oil and install it in Motor
Housing with the side hole nearest to Seal pointed toward Rotor (22).

4. Position Reverse Lever (12) on Reverse Valve and while using a thin
blade screwdriver to depress Reverse Lock Plunger, push Lever onto
Reverse Valve.

5. Place a new Handle Gasket (17) on the Motor Housing.

6. Examine Reverse Valve Seal (11) located inside Handle and if it is
nicked, deformed or worn, remove it and install a new Seal.

7. Fill rotor cavity in Handle with recommended grease and position
Handle on the Motor Housing.

8. For 3940 and 3942 Series: Install four Handle Cap Screws (15) and
using an alternate tightening pattern, tighten Screws to between 10
and 12 ft-lb (14 and 16 Nm) torque.
For 3955 Series: Install four Handle Cap Screws (15) and using an
alternate tightening pattern, tighten Screws to between 25 and 28 ft­lb (34 and 38 Nm) torque.

9. Move Reverse Lever through the forward and reverse positions to
make certain the Lever locks in position.

10. Turn assembly in vise jaws and clamp on Handle with rotor shaft
upward.

11. Pack Front Rotor Bearing with additional grease and rotate rotor
shaft. If shaft does not rotate smoothly, rap end of rotor shaft with a
soft hammer to set motor and try to rotate shaft again.