FSB 252-034 Service Bulletin/Repair Instructions

Mack Trucks

Greensboro, NC USA
Field Service Bulletin

Trucks

Date
Group
No.
Release
Page
4.2021
252
034
04
1(9)
Cab Mounted Exhaust Bracket, Replacement

CHU, CXU, GU, PI, AN, GR
FSB 252-034, Cab Mounted Exhaust Bracket,

Replacement

(April 2021).

An improved exhaust support bearing, and bracket has been introduced into production

starting November 2020. This improved design will now be the repair solution for all trucks

built with the on-cab exhaust support design. The following information is a compliment to

TPI 252–051.
Required Parts

Part Description
Part number
Quantity
O-rings
977890
2
Bearing
23682580
1
Snap ring
23710292
2
Bracket
23706631
1
Note: If applicable upgraded shaft may be needed, reference step 10.
PV729-FSB252-034_M
USA155942070
Mack Trucks

Field Service Bulletin
Date

4.2021
Group
No.
Release
252
034
04
Procedure

1 Remove the nut securing the rubber mount isolator rod at upper stack mount..
C2171692
2 Loosen the upper exhaust stack mounting strap nut
C2171693
Page

2(9)
Mack Trucks

Field Service Bulletin
Date

4.2021
Group
No.
Release
252
034
04
3 Slide the upper mounting bracket and upper rubber isolator rod bushing up the exhaust

pipe.

Note: Inspect the upper and lower rubber isolator rod bushings for excessive wear.

Replace as necessary.
C2171694
4 Remove the spherical mounting bracket bolts.
C2171695
Page

3(9)
Mack Trucks

Field Service Bulletin
Date

4.2021
Group
No.
Release
252
034
04
5 Remove the spherical bearing and bracket from the isolator rod and discard.
C2171696
6 Assemble the new bearing assembly.

Note: Install the O-rings onto the Bearing, two most center groves.
C2171697
Page

4(9)
Mack Trucks

Field Service Bulletin
Date

4.2021
Group
No.
Release
252
034
04
7 Lubricate the bearing.

8 install bearing into the bracket.

Note: Recommend lubricant, Waylube oil, Light weight oil, Petroleum based grease or 3in-1 oils, do not use WD-40, PFTE sprays Fluorocarbons, Silicon oils grease or spray.
C2171698
9 Install Snap rings.
C2171699
C2171700
Page

5(9)
Mack Trucks

Field Service Bulletin
Date

4.2021
Group
No.
Release
252
034
04
10 Install the assembled exhaust bearing assembly by sliding over the insulator rod and

attaching to the existing mounting bracket on the cab side, (TOP) Lettering facing up.

Note: Do not lubricate the shaft.

Note: If unit was built with guide shaft part number 21398996, (which can be identified

with a 15.8 mm isolator rod diameter) it will need to be upgraded to the most current part

number before installing the new bearing assembly.

11 Install the mount bracket bolts

12 , Torque tighten to 48± 8Nm (35+-6 lb-ft).
C2171701
Page

6(9)
Mack Trucks

Field Service Bulletin
Date

4.2021
Group
No.
Release
252
034
04
13 Install the upper mounting bracket and upper rubber isolator rod bushing.

Tighten the mounting nut for the upper rubber mount isolator rod to 35±2Nm.

Note: Do not tighten the exhaust strap fastener at this time.
C2171702
C2171703
14 Connect the batteries.

15 Start the engine allow system air pressure to build. Turn the engine off.

16 Verify the cab ride height is correct. Refer to 8181-05-02-06 Rear Cab Mount Alignment,

Adjustment
Page

7(9)
Mack Trucks

Field Service Bulletin
Date

4.2021
Group
No.
Release
252
034
04
17 Measure the distance from the bottom of the bearing mounting bracket to the bottom of

the upper isolator rod bushing should be a maximum of 58 mm (2.3 in).

Note: If an adjustment must be made, loosen the lower exhaust stack mounting strap

fastener and adjust the upper and/or lower mounting bracket and isolator rod bushing up

or down so that the correct distance is obtained.
C2171704
18 Torque tighten the mounting strap fastener(s) to 40 ±5 Nm (30 ±4 lb-ft).
C2171705
19 Remove the wheel chocks return to service.
Page

8(9)
Mack Trucks

Field Service Bulletin
Date

4.2021
Group
No.
Release
252
034
04
Reimbursement

This repair may be eligible for reimbursement if a product failure

was experienced within time and mileage limits of the applicable

Warranty coverage. Reimbursement is obtained via the normal

claim handling process.
Reimbursement

UCHP
Claim Type (used only when uploading from the Dealer Bus.

Sys.)
01
Labor Code

Primary Labor Code
2527–03–0901

(0.5 hrs)
Causal Part
21900242
Mack Trucks Inc. reserves the right to make any changes in design or to make additions to or

upon its products without incurring any obligations to install the same on vehicles previously

built.
Page

9(9)

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