NHTSA ID Number: 11020949
Manufacturer Communication Number: SI10-800-160
TSB/Document Date: 2025-07-29
Summary
Suspect Population: Certain 2021 through 2026 Blue Bird BBCV buses, equipped with a 217” WB flat floor & Ford
7.3L powered engine. Condition:Chassis web fractures in or around the vicinity of the LF shock mount Root Cause Identification and Justification: • FEA modeling shows elevated regions of stress in proximity of the upper fastener hole for the LH shock mount resulting from several external influences. The highest stress stemming from shock extension forces in curb hop scenarios. • Bearing in mind the absence of this failure mode on standard floor chassis designs with substantially higher usage, the projected stress in this region of 4582 PSI is used as an objective bench mark of the acceptable upper limit. • Two corrective solutions are being executed as pragmatic countermeasures to correct this failure mode, based on the severity and frequency of the crack, if present. Repair plate 1 being the latest evolution. FEA analysis & ref chart below • Installation of this repair plate decreases the stress in this region to less than the standard floor chassis baseline allowing us to predict this solution to last the expected life of the chassis.
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TSB/Document ID: SI10-800-160
Replacement Service Bulletin Number:
MFR Communication Date: 2025-07-29
MFR Internal Campaign ID/Software Version:
Communication Type: Service Bulletin/Repair Instructions
NHTSA Components: UNKNOWN OR OTHER
MFR Component System:
MFR Component Subsystem:
Previous TSB | Next TSB |
Service
Instructions
SI10-800-160 – Frame Web Cracks, 217” WB Flat Floor
Suspect Population: Certain 2021 through 2026 Blue Bird BBCV buses, equipped with a 217” WB flat floor & Ford 7.3L
powered engine.
Condition: Chassis web fractures in or around the vicinity of the LF shock mount
Root Cause Identification and Justification:
• FEA modeling shows elevated regions of stress in proximity of the upper fastener hole for the LH shock mount resulting from
several external influences. The highest stress stemming from shock extension forces in curb hop scenarios.
• Bearing in mind the absence of this failure mode on standard floor chassis designs with substantially higher usage, the
projected stress in this region of 4582 PSI is used as an objective bench mark of the acceptable upper limit.
• Two corrective solutions are being executed as pragmatic countermeasures to correct this failure mode, based on the severity
and frequency of the crack, if present. Repair plate 1 being the latest evolution. FEA analysis & ref chart below
• Installation of this repair plate decreases the stress in this region to less than the standard floor chassis baseline allowing us to
predict this solution to last the expected life of the chassis.
Modeled Stress in Failure Region
Baseline
Standard Floor
(psi)
Baseline Flat
Floor (psi)
Repair Plate 1
Model (psi)
Vertical 1G, Shock
Up
4,582
7,151
1,186
Vertical 1G, Shock
Down
2,438
15,247
2,012
Curb Hop, Shock
Up
4,129
4,615
1,586
Curb Hop, Shock
Down
3,226
20,009
3,037
Conditions
Service
Instructions
SI10-800-160 – Frame Web Cracks, 217” WB Flat Floor
Corrective Action: Perform an inspection of the area defined below. Reference page 3 for defining criteria on which repair option, if any, to affect.
Component Code: 10-800-160
SRTs:
•
•
•
Inspection- .2
Small Plate/Solution1- 3.12 HRS
Large Plate/Solution2- 4.90 HRS
Note:
Ensure that all federal & local safety protocol is followed. Park bus on appropriate flat/level surface, LOTO the vehicle, and chock the wheels.
Service
Instructions
SI10-800-160 – Frame Web Cracks, 217” WB Flat Floor
Repair Criteria:
Repair Criteria
Examples
Repair Plate 1
Repair Plate 2
101mm(4 inches)
Number of Cracks
1
1 or More
Region of Crack
A
B
Crack Length
Region A
Crack
Length
Crack
Region
Number of
Cracks
Repair
Solution
Example 1
60mm
A
1
A
Example 2
45mm
A
2
B
Example 3
105mm
B
1
B
Region B
Service
Instructions
Severity Detection Example
Crank Length- 45mm
Crack Quantity- 1
Solution- Repair Plate 1
SI10-800-160 – Frame Web Cracks, 217” WB Flat Floor
Service
Instructions
SI10-800-160 – Frame Web Cracks, 217” WB Flat Floor
Repair Options:
Repair Plate 1
Part Number 10086463
Repair Plate 2
Part Number 10083663
Service
Instructions
SI10-800-160 – Frame Web Cracks, 217” WB Flat Floor
Relevant Repair Parts
REPAIR PLATE 2
REPAIR PLATE 1
BRACKET ASSY,SHOCK,SPRG SUSP,FRT,LH,SP BBCV
WASHER,FLAT,21/32 X 1 1/8 X 3/32,HDN,YEL ZN
NUT,HEX HD,5/8-11,GR 8,LOCK,CADMIUM WAX, (25)
CAPSCREW,HEXHD,3/8-16NCX1-1/2,GR8,YELZNDICH
WASHER,FLAT,3/8 SAE,HDN,BLK ZN
NUT,HEX HD,3/8-16 LOCK,YEL ZN DICH
CAPSCREW,HEX HD,1/2-13 X1 1/2,GR8,YELZNDICH
WASHER,FLAT,17/32 X 1 1/16 X 7/64,HDN,BLKZN
NUT,HEX HD,1/2-13,LOCKING,GR 8,CAD WAX
CAPSCREW,HEX HD,5/8-11 X 2 1/4,GR8
CAPSCREW,HEX HD,5/8-11 X1 3/4,GR8,YELZNDICH
NUT,HEX,3/4-10,PRVLG TORQ,GR8,CAD WAX
10086463
00929018
00939827
00803171
01107085
00826297
00803239
01003045
00850800
02604916
01107879
00933879
1
14
7
1
2
1
3
6
3
3
4
1
BRACKET ASSY,SHOCK,SPRG SUSP,FRT,LH,SP BBCV
WASHER,FLAT,21/32 X 1 1/8 X 3/32,HDN,YEL ZN
NUT,HEX HD,5/8-11,GR 8,LOCK,CADMIUM WAX, (25)
CAPSCREW,HEXHD,3/8-16NCX1-1/2,GR8,YELZNDICH
WASHER,FLAT,3/8 SAE,HDN,BLK ZN
NUT,HEX HD,3/8-16 LOCK,YEL ZN DICH
CAPSCREW,HEX HD,1/2-13 X1 1/2,GR8,YELZNDICH
WASHER,FLAT,17/32 X 1 1/16 X 7/64,HDN,BLKZN
NUT,HEX HD,1/2-13,LOCKING,GR 8,CAD WAX
CAPSCREW,HEX HD,5/8-11 X 2 1/4,GR8
CAPSCREW,HEX HD,5/8-11 X1 3/4,GR8,YELZNDICH
NUT,HEX,3/4-10,PRVLG TORQ,GR8,CAD WAX
10083663
00929018
00939827
00803171
01107085
00826297
00803239
01003045
00850800
02604916
01107879
00933879
1
14
7
1
2
1
13
26
13
3
4
1
Service
Instructions
SI10-800-160 – Frame Web Cracks, 217” WB Flat Floor
Tools/Materials Needed:
Item description
2x4 shoring lumber, 12 3/4" long
Mag Drill
Hammer
Annular Cutter, 9/16, Cobalt
Cutting Oil
4" Grinder w/ .065 abrasive cutoff wheel
17/32" Transfer Punch
#30(1/8) drill bit, cobalt/carbide
15/16" Open end wrench
1/2" Open end wrench
1/2" Torque wrench
Cold Chisel, 12"
Grainger P/N
811EE2
4WNL8
5HD99
22N816
4GB71
Quanity
1
1
1
1
1
1
1
Link To Purchase
Service
Instructions
SI10-800-160 – Frame Web Cracks, 217” WB Flat Floor
Recommended Preparatory Steps:
1.
2.
Power Wash LF fender well area
Apply penetrant oil to all 6 fender extension studs, WD-40 or equivalent
Instructions:
1.
2.
3.
4.
Start engine and turn steering wheel to full right lock. Shut down engine and install shoring lumber between LH engine mount and leaf spring.
LOTO(Lock Out Tag Out) the vehicle. Recommend disconnecting the J13 connector from the chassis PCB
Remove LH mudflap assy(if equipped) and fender extension from the cowl and place to the side. Save fasteners for re-use.
Remove LH shock assy from the upper bracket and fully compress for accessibility
Service
Instructions
5.
6.
7.
SI10-800-160 – Frame Web Cracks, 217” WB Flat Floor
Remove all fasteners as described in FIG1
Identify and center punch the end(s) of existing crack(s). Stop
drill with #30 drill bit.
Temp up the relevant repair plate, and using the proper
transfer punch, mark the holes required for drilling
Photo of crack stop drill
Photo of Transfer Punch
Service
Instructions
8.
9.
10.
SI10-800-160 – Frame Web Cracks, 217” WB Flat Floor
Setup Mag Drill with 9/16” annular Cutter, engage pilot into
marks made from transfer punch
Bore 3 holes, going slow with proper oil.
Cut & remove Huckspin™ collar and remove bolt.
Photo of marking holes
Photo of Mag Drill
Service
Instructions
11.
12.
SI10-800-160 – Frame Web Cracks, 217” WB Flat Floor
ONLY If installing the large repair plate per page 3, remove
the huck collars off the lower frame stiffener.
Remove Huck bolts then remove the stiffener
REMOVE
PAY ATTENTION!
ONLY DO THIS STEP IF INSTALLING
THE LARGE REPAIR PLATE
Service
Instructions
Instructions cont’d
13.
14.
15.
Install relevant repair plate, selecting and torquing the
fasteners defined on page 13.
Replace previously removed components.
Remove shoring lumber, LOTO, and return to service
Note:
Chassis repair plate is installed with threaded fasteners. These
fasteners require inspection and re-torque every 12 months or 12k
miles, whichever occurs first.
SI10-800-160 – Frame Web Cracks, 217” WB Flat Floor
Service
Instructions
SI10-800-160 – Frame Web Cracks, 217” WB Flat Floor
Fastener Selection & Torque Chart:
Bolt Description
Bolt p/n
Fastener
Location
Fastener
Torque(FT-lbs)
5/8x11x1 ¾
01107879
A
138-159
5/8x11x2 ¼
02604916
B
138-159
1/2x13x1 ½
00803239
C
70-80
3/8x16x1 ½
00803171
D
24-27
3/4x10x4”
00870873
E
210-220
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