Bendix® TW-7 Valve Differential Lock Field Maintenance Kit
DESCRIPTION

KIT CONTENTS

The Bendix® TW-7 Valve Differential Lock Field Maintenance
Kit, Bendix® part number K288580, is available to service two
variants of the TW-7 valve, Bendix part numbers 285508 and
284388. See Figure 1.

Refer to Table 1 for the contents of the TW-7 maintenance kit.
Quantity

Description

Item No.

1

Rubber Boot

2

1

O-ring

4

1

O-ring

10

1

Inlet and Exhaust Valve

12

1

Tube of Lubricant

Not Shown

Table 1 – Kit Contents

TW-7 Valve Part Number 284388

TW-7 Valve Part Number 285508
1

1

TW-7 Valve Part Number 285508
2*

2*
3
4*

4*
6

19

5

6

18

7

9

10*

17

11
16

16

13

No.

No.

Item

No.

Item

1

Plunger

6

Washers

11

Valve Body

16

Spring

2*

Rubber Boot

7

Lock Washer

12*

Inlet and Exhaust Valve

17

Exhaust Breather

3

Cap Nut

8

Piston

13

Retainer

18

Spring

4*

O-ring

9

Piston Spring

14

O-ring

19

Retaining Ring

5

Mounting Nut

10*

Piston O-ring

15

Cap Nut

Figure 1 – TW-7 Maintenance Kit

1

Item

12*

14
15

15
Item

10*

11

14
No.

7

17

12*

13

5

8

8
9

3

*: Included in Kit K288580

GENERAL SAFETY GUIDELINES

WARNING! PLEASE READ AND
FOLLOW THESE INSTRUCTIONS
TO AVOID PERSONAL INJURY OR DEATH:

When working on or around a vehicle, the following
guidelines should be observed AT ALL TIMES:
▲Park the vehicle on a level surface, apply the parking
brakes and always block the wheels. Always wear personal
protection equipment.
▲Stop the engine and remove the ignition key when working
under or around the vehicle. When working in the engine
compartment, the engine should be shut off and the ignition
key should be removed. Where circumstances require that
the engine be in operation, EXTREME CAUTION should be
used to prevent personal injury resulting from contact with
moving, rotating, leaking, heated or electrically-charged
components.
▲Do not attempt to install, remove, disassemble or
assemble a component until you have read, and thoroughly
understand, the recommended procedures. Use only the
proper tools and observe all precautions pertaining to use
of those tools.
▲If the work is being performed on the vehicle’s air brake
system, or any auxiliary pressurized air systems, make
certain to drain the air pressure from all reservoirs before
beginning ANY work on the vehicle. If the vehicle is
equipped with a Bendix® AD-IS® air dryer system, a Bendix®
DRM™ dryer reservoir module, a Bendix ® AD-9si ®, AD-HF®,
or AD-HFi ® air dryer, be sure to drain the purge reservoir.
▲Following the vehicle manufacturer’s recommended
procedures, deactivate the electrical system in a manner
that safely removes all electrical power from the vehicle.
▲Never exceed manufacturer’s recommended pressures.
▲Never connect or disconnect a hose or line containing
pressure; it may whip and/or cause hazardous airborne
dust and dirt particles. Wear eye protection. Slowly open
connections with care, and verify that no pressure is
present. Never remove a component or plug unless you are
certain all system pressure has been depleted.
▲Use only genuine Bendix ® brand replacement parts,
components and kits. Replacement hardware, tubing, hose,
fittings, wiring, etc. must be of equivalent size, type and
strength as original equipment and be designed specifically
for such applications and systems.
▲Components with stripped threads or damaged parts should
be replaced rather than repaired. Do not attempt repairs
requiring machining or welding unless specifically stated
and approved by the vehicle and component manufacturer.
▲Prior to returning the vehicle to service, make certain all
components and systems are restored to their proper
operating condition.
▲For vehicles with Automatic Traction Control (ATC), the ATC
function must be disabled (ATC indicator lamp should be
ON) prior to performing any vehicle maintenance where
one or more wheels on a drive axle are lifted off the ground
and moving.
▲The power MUST be temporarily disconnected from the
radar sensor whenever any tests USING A DYNAMOMETER
are conducted on a vehicle equipped with a Bendix ®
Wingman ® system.
▲You should consult the vehicle manufacturer's operating
and service manuals, and any related literature, in
conjunction with the Guidelines above.

2

REMOVAL
See Figure 1.
Ensure the vehicle is safe to work on before beginning. Follow
all General Safety Guidelines in this document.
1. Block and hold the vehicle on a level surface by means
other than the air brakes.
2. Drain the air pressure from all reservoirs.
3. Mark the airlines and their connections to the TW-7 valve
and disconnect them.
4. Remove and discard the rubber boot (2).
5. Loosen, remove, and retain the mounting nut (5), washers
(6), and lock washer (7).

DISASSEMBLY
See Figure 1.
1. Remove and retain the cap nut (3).
2. If after removing the cap nut a spring is present, remove
and retain the spring (18) from the plunger. This step
applies only to TW-7 valve part number 285508.
3. Remove and retain the plunger (1) and remove and
discard the o-ring (4).
4. Remove and retain the piston (8) from the valve body (11).
5. Remove and discard the piston o-ring (10).
6. Remove and retain the piston spring (9).
7. Remove and retain the cap nut (15) and o-ring (14).
8. Remove and retain the spring (16) and retainer (13).
9. Remove and discard the inlet and exhaust valve (12).
10. Do not remove exhaust breather (17).
11. If applicable, do not remove retaining ring (19) from the
plunger (1). This step applies only to TW-7 valve part
number 285508.

ASSEMBLY

OPERATING AND LEAKAGE TESTS

See Figure 1.
1. Prior to assembly, lubricate the o-rings and bearing
surfaces with the lubricant included in the maintenance kit.
2. Install the new o-ring (10) on the piston (8).
3. Install the new o-ring (4) on the plunger (1).
4. Install the new inlet and exhaust valve (12), the retained
spring (16), and the retained retainer (13) in the valve
body (11).
5. Install the o-ring (14) on the cap nut (15), then install both
in valve body (11) and torque to 50-150 in-lbs (6-17 N•m).
6. Install the piston spring (9) and piston (8) into the valve
body (11).
7. Install the plunger (1) into the cap nut (3).
8. If applicable, install the plunger spring (18) in the valve
body (11) along with the plunger (1) and cap nut (3).
Torque to 150-400 in-lbs (17-45 N•m). The spring (18)
installation step applies only to TW-7 valve part
number 285508.

IMPORTANT
It is recommended that the operating and leakage tests
be performed prior to installation on the vehicle.
1. Connect a 120 psi air source to the supply. An accurate
test gauge should be tee'd into each airline and a means
of controlling the air pressure provided.
2. A small volume with a gauge should be connected to
the delivery port.
3. With 120 psi supply pressure and the valve in the released
position (plunger up), the gauge at the delivery port
should read 0 psi.
4. Leakage at the exhaust port should not exceed a 1-in.
bubble in five (5) seconds. No leakage is permitted
between the body and the lower cap nut (15).
5. With 120 psi supply pressure, operate the valve (push
plunger down). The gauge at the delivery port should
read 120 psi.
6. Leakage at the exhaust port and between the body and
the upper cap nut (3) should not exceed a 1-in. bubble
in five (5) seconds.
7. The valve must return to the release position without
assistance when the manual force is removed.

INSTALLATION
See Figure 1.
1. Mount the TW-7 valve using the retained lock washer
(7), washers (6), and mounting nut (5).
2. Install the new rubber boot (2).
3. Connect the airlines to the proper ports of the TW-7 as
marked during their removal.

TECHNICAL ASSISTANCE
For additional assistance, the Bendix Tech Team can
be reached by email at techteam@bendix.com or by
phone at 1-800-AIR-BRAKE (1-800-247-2725), option 2.
Representatives are available Monday through Thursday,
8:00 a.m. – 6:00 p.m., and Friday, 8:00 a.m. – 5:00 p.m. ET.

24/7/365 ACCESS
FULL SERVICE AT YOUR FINGERTIPS

24/7/365 ACCESS
FULL SERVICE AT YOUR FINGERTIPS

3

1-800-AIR-BRAKE (1-800-247-2725)
TECHTEAM@BENDIX.COM

1-800-AIR-BRAKE (1-800-247-2725)
TECHTEAM@BENDIX.COM

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