NHTSA ID Number: 10200219
Manufacturer Communication Number: FSB 722 004
TSB/Document Date: 2021-08-09
Summary
Twin Y Suspension, Trailing Blade, Replacement. Some MACK
CHU and CXU trucks built 06/13/2013 through 09/25/2015 and equipped with Twin-Y suspension may require replacement of the Twin-Y trailing blades with a more robust design. The new Twin-Y trailing blades have a new profile with a stronger material thickness of 7.0 mm (0.28 in). All four trailing blades will require replacement in this repair procedure.
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TSB/Document ID: FSB 722 004
Replacement Service Bulletin Number:
MFR Communication Date: 2015-10-30
MFR Internal Campaign ID/Software Version:
Communication Type: Service Bulletin/Repair Instructions
NHTSA Components: ELECTRONIC STABILITY CONTROL:AUTOMATIC (ASC)
MFR Component System:
MFR Component Subsystem:
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Mack Trucks, Inc.
Greensboro, NC USA
Field Service Bulletin
Trucks
Date
Group
No.
Release
Page
10.2015
722
004
01
1(21)
Twin-Y Suspension, Trailing Blade,
Replacement
CHU, CXU
(Meritor/Dana Axles)
FSB 722-004, Twin Y Suspension, Trailing Blade,
Replacement
(October 2015)
Some MACK CHU and CXU trucks built 06/13/2013 through 09/25/2015 and equipped with
Twin-Y suspension may require replacement of the Twin-Y trailing blades with a more robust
design. The new Twin-Y trailing blades have a new profile with a stronger material thickness
of 7.0 mm (0.28 in). All four trailing blades will require replacement in this repair procedure.
Follow the repair procedure outlined in this Field Service Bulletin (FSB) for replacement of the
existing Twin-Y trailing blades with the newly designed trailing blades and hardware. See the
tables on pages 2 and 3 for required parts.
This bulletin does not apply to MACK Trucks Australia.
PV729-FSB722-004_M
USA72260
Mack Trucks, Inc.
Field Service Bulletin
Date
10.2015
Group
No.
Release
722
004
01
W7104594
Required Parts
Twin-Y Suspension, Trailing Blade, Replacement Parts
Item
Description
Part Number
Qty
1
Trailing Blade **
22491332
2
1
Trailing Blade ***
22491343
2
1
Trailing Blade ****
22491338
2
2
Pivot bolt, M22 X220, Huck 360 Bolt
22496392
4
3
Pivot Bolt Collar, M22 X 26.4, Huck 360 Nut
22496430
4
4
Axle Seat Bolts, M18 X 110, Huck 360 Bolt
22356967
16
5
Axle Seat Bolt Collar, M18 X 21.6, Huck 360
Collar
22356966
16
6
Washer M19*34*3
60110294
16
7
Hanger Bracket
21684150
As
Required
** Applies to all front axles
*** Applies to all Meritor / Dana Axles (RT1850SE)
**** Applies to all Meritor / Dana Axles (RTS1850D)
Page
2(21)
Mack Trucks, Inc.
Field Service Bulletin
Date
10.2015
Group
No.
Release
722
004
01
Twin-Y Suspension, Trailing Blade, Replacement Parts (Continued)
Item
Description
Part Number
Qty
8
Hanger Bracket Bolt, 14 87-64
21475330
2#
9
Hanger Bracket Bolt, 14 97-74
21638411
2#
10
Hanger Bracket Bolt 14 107-84
21475333
2#
11
Hanger Bracket Bolt 14 142-119
21710877
2#
12
Hanger Bracket Bolt 20 115-68
22438561
2#
13
Hanger Bracket Bolt Collar 14*21
21475706
8#
14
Hanger Bracket Bolt Collar 20*29
22410765
2#
Note: # These quantities listed in this table are per hanger bracket.
Decommissioning the Truck for Repair
You must read and understand the precautions and guidelines in Service Information,
group 70, "General Safety Practices, Frame, Springs, Shocks & Wheels" before performing
this procedure. If you are not properly trained and certified in this procedure, ask your
supervisor for training before you perform it.
NOTE: Information is subject to change without notice. Illustrations are used for reference
only and can differ slightly from the actual vehicle being serviced. However, key
components addressed in this information are represented as accurately as possible.
1 Park the vehicle on a flat and level surface.
2 Apply the parking brake.
3 Place the transmission in neutral or park.
4 Install the wheel chocks.
W7086748
Page
3(21)
Mack Trucks, Inc.
Field Service Bulletin
Date
10.2015
Group
No.
Release
722
004
01
5 Disconnect the cable from the battery’s negative terminal.
W3086747
Twin-Y Suspension, Trailing Blade, Replacement
Procedure
1 Following safe lifting procedures, lift and support both the frame and axle housings.
2 Remove the wheel nuts.
3 Remove the wheels.
W7104595
Page
4(21)
Mack Trucks, Inc.
Field Service Bulletin
Date
10.2015
Group
No.
Release
722
004
01
4 Release the park brake.
5 Back off the brakes (slack adjusters).
W7104596
6 Cage the brake chambers.
W7104597
Page
5(21)
Mack Trucks, Inc.
Field Service Bulletin
Date
10.2015
Group
No.
Release
722
004
01
7 Remove the brake drums.
W7104598
8 Remove the brake linings, brake springs and rollers.
W7104599
Page
6(21)
Mack Trucks, Inc.
Field Service Bulletin
Date
10.2015
Group
No.
Release
722
004
01
9 Loosen the pivot bolt (1) securing the trailing blade to the frame hanger bracket (left side).
Note: Before loosening the pivot bolt (left side), mark the cam adjustment washers (2) for
re-installation.
W7104600
10 Loosen the pivot bolt and collar securing the trailing blade to the frame hanger bracket
(right Side).
W7104601
Page
7(21)
Mack Trucks, Inc.
Field Service Bulletin
Date
10.2015
Group
No.
Release
722
004
01
11 Remove the fasteners securing the trailing blade to the top plate and spring seat.
Note: Discard the fasteners. Do not reuse.
W7104602
12 Remove the loosened pivot bolt collars (1), pivot bolts (2) and cam adjustment washers at
frame hanger brackets (left side).
Note: Discard the pivot bolt collars and pivot bolts. Do not reuse.
W7104603
Page
8(21)
Mack Trucks, Inc.
Field Service Bulletin
Date
10.2015
Group
No.
Release
722
004
01
13 Remove the pivot bolt (1), collar and washers (2) at the frame hanger bracket (right side).
Note: Discard the pivot bolt collars and pivot bolts. Do not reuse.
W7104604
14 With assistance, remove the trailing blades from the axle and frame hanger brackets.
W7104605
Page
9(21)
Mack Trucks, Inc.
Field Service Bulletin
Date
10.2015
Group
No.
Release
722
004
01
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