NHTSA ID Number: 10083596
Manufacturer Communication Number: PI 0827
TSB/Document Date: 2016-10-26
Summary
A NUMBER OF PRE PRODUCTION VEHICLES HAVE BEEN BUILT EQUIPPED WITH THE TWIN Y AIR SUSPENSION. UPON REVIEW OF THESE VEHICLES IT HAS BEEN DETERMINED THAT SOME HAVE DEFECTIVE BUSHINGS WITHIN THE TOP PLATE AND SPRING SEAT.
Mack Trucks
, Inc.
Greensboro, NC USA
Service Program
Trucks
Date
Group
No.
Release
Page
8.2013
722
002
1
1(32)
Top Plate and Spring Seat, Replacement
CHU, CXU
PI0827, Top Plate and Spring Seat, Replacement
(August 2013)
Note: Information is subject to change without notice.
Illustrations are used for reference only and may differ slightly from the actual vehicle being
serviced. However, key components addressed in this information are represented as
accurately as possible.
A number of Pre Production vehicles have been built equipped with the Twin Y Air
Suspension. Upon review of these vehicles it has been determined that some have defective
bushings within the top plate and spring seat. To address the defective bushings, this bulletin
as been created which covers parts involved (Table 1 and Figure 1) , a procedure for
inspection and a procedure for replacement of the top plate and spring seat, if replacement is
found necessary.
PV729-PI0827
USA60163
Mack Trucks, Inc.
Service Program
Date
8.2013
Group
No.
Release
722
002
1
Table 1 contains a complete list of service parts that may be required to the fix the bushing
problem. Figure 1 shows the location of the these parts.
Service Parts (Table 1)
Part Number
Description
Quantity
21799969
Top Plate (LH)
1 per Wheel
21799970
Top Plate (RH)
1 per Wheel
21947030
Spring Seat (LH)
1 per Wheel
21947031
Spring Seat (RH)
1 per Wheel
21759985
Service U Bolts
2 per Wheel
947971
U Bolt Fasteners
4 per Wheel
995681
Y Blade to Seat Fasteners
(M18)
4 per Wheel
22035866
Y Blade to Seat Fasteners
(Nuts)
4 per Wheel
22039810
Y Blade to Seat Fasteners
(Spring Washer)
4 per Wheel
990861
S Cam Tube Support
Bracket Fastener
1 per Wheel
996522
Set Screw for Pressure
Plate
1 per Wheel
Page
2(32)
Mack Trucks, Inc.
Service Program
Date
8.2013
Group
No.
Release
722
002
1
W7083166
Figure 1 Location of Service Parts
1 — Y Blade (Shown for reference only not listed as a replacement part)
2 — Top Plate (Shown in table 1 as LH and RH)
3 — Spring Seat (Shown in table 1 as LH and RH)
4 — Service U bolts
5 — Fasteners for Service U bolts
6 — Bushing within Y blade at hanger bracket (Shown for reference only not listed as a
replacement part)
7 — Fasteners for Top Plate and Spring Seat (M18)
8 — Fasteners for Top Plate and Spring Seat (Nuts)
9 — Fasteners for Top Plate and Spring Seat (Spring Washers)
10 — Pressure Plate (Shown for reference only not listed as a replacement part)
11 — Set Screw for Pressure Plate
12 — Spring Seat Bushings (If bushings are found defective the Spring Seat will be replaced
which includes new bushings)
13 — Top Plate Bushings (If bushings are found defective the Top Plate will be replaced
which includes new bushings)
Page
3(32)
Mack Trucks, Inc.
Service Program
Date
8.2013
Group
No.
Release
722
002
1
Inspection Procedure
TWIN Y AIR SUSPENSION BUSHING INSPECTION
1. Visual inspection, do the Y blades make contact with the outer shell of the bushing? See
figures for pass or fail. If passes, continue with Step 2. If fails, proceed to the Top Plate and
Spring Seat, Replacement procedure on page 7.
W7083167
PASS
W7083168
FAIL
Page
4(32)
Mack Trucks, Inc.
Service Program
Date
8.2013
Group
No.
Release
722
002
1
2. Measure the distance between the Y blades as close as possible to top plate and spring
seat (dimension A). If the distance is less than 64.7 mm (2.55 in) it fails. If fails, proceed to the
Top Plate and Spring Seat, Replacement procedure on page 7. If test passes, continue with
Step 3.
W7083170
Page
5(32)
Mack Trucks, Inc.
Service Program
Date
8.2013
Group
No.
Release
722
002
1
3. Check torque on top plate and spring seat fasteners with torque wrench set to
135 Nm (100 ft-lb). If the torque wrench moves more than approximately 10 degrees the test
fails. If test fails, proceed to the Top Plate and Spring Seat, Replacement procedure on
page 7. If test passes, continue with Step 4.
W7083169
4. Check torque on top plate and spring seat fasteners with torque wrench set to
271 Nm (200 ft-lb). If the torque wrench moves more than approximately 10 degrees the test
fails. If test fails, proceed to the Top Plate and Spring Seat, Replacement procedure on
page 7. If test passes, continue with Step 5.
5. Check torque on top plate and spring seat fasteners with torque wrench set to
407 Nm (300 ft-lb). If the torque wrench moves more than approximately 10 degrees the test
fails. If test fails, proceed to the Top Plate and Spring Seat, Replacement procedure on
page 7.
Note: If the bushings pass this final torque test, the bushings are not defective and the
procedure is complete and no further action will be required.
Page
6(32)
Mack Trucks, Inc.
Service Program
Date
8.2013
Group
No.
Release
722
002
1
Top Plate and Spring Seat, Replacement
REMOVAL
1. Park the vehicle on a flat level surface. Place the shift lever in neutral. Apply the parking
brake. Chock the front wheels.
2. Disconnect all cables from the negative (ground) battery terminals to prevent personal
injury from electrical shock and prevent damage to electrical components.
3.
DANGER
Failure to properly support the front of the axle housing may result in the axle rolling
forward, causing serious injury or death.
Following safe lifting guidelines, lift and support both the frame and the axle housing.
4. Remove the wheels and tires.
5. Release the parking brake.
6. Cage the brake chamber.
7. Back-off the brake slack adjuster so that the brake drum can be removed.
8. Remove the brake drum.
W5072399
Page
7(32)
Mack Trucks, Inc.
Service Program
Date
8.2013
Group
No.
Release
722
002
1
9. Remove the brake shoes.
W7072862
Hub Removed For Illustration Purpose Only
10.
CAUTION
The weight of the axle housing is not distributed evenly. Make sure the jack can safely
support the axle housing before removing the trailing blade bolts. If the axle housing is not
supported properly, the housing can fall off the jack and result in component damage.
Before loosening the trailing blade fastener (left side), mark the adjusting washers for reinstallation.
Loosen the fastener securing the trailing blade to the hanger bracket (right side).
Note: Use care when loosening the trailing blade fastener, so that the fastener is not
damaged.
Page
8(32)
Mack Trucks, Inc.
Service Program
Date
8.2013
W6072195
Left Side Shown
W7072863
Right Side Shown
Group
No.
Release
722
002
1
Page
9(32)
Mack Trucks, Inc.
Service Program
Date
8.2013
Group
No.
Release
722
002
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TSB/Document ID: PI 0827
Replacement Service Bulletin Number:
MFR Communication Date: 2013-08-12
MFR Internal Campaign ID/Software Version:
Communication Type: Service Bulletin/Repair Instructions
NHTSA Components: SUSPENSION
MFR Component System:
MFR Component Subsystem:
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