Exhaust Flex Pipe Cracks

M-252-001

(January 2009)

Valid for

All CXU,CHU,GU,TD models with MP7, MP8 built before May 2008

Case description

Effective May 9, 2008, a redesigned exhaust flex pipe and turbocharger outlet pipe (located between the turbocharger
cast diffuser and the exhaust flex pipe) were implemented into production on CXU, CHU and GU model chassis. Both the
turbocharger outlet pipe and the exhaust flex pipe were redesigned to improve exhaust pipe alignment, and the diameter
of the inside liner of the flex pipe was reduced by 6.35 mm (1/4") to prevent contact with the pipe bellows. These changes
were made to prevent the exhaust flex pipe from cracking. Should a cracked exhaust flex pipe be encountered on a
chassis manufactured prior to May 9, 2008, the existing flex pipe and turbocharger outlet pipe should be replaced with
these revised components.

Note: Not applicable to Mack Trucks Australia.

Parts

Revised Exhaust Flex and Turbocharger Outlet Pipes

ZS

Key

Qty.

Part number

Description

Replaces

1

1

21095726

Gasket, flex pipe-to-intermediate

pipe
2 1 21021850 Clamp, V-band, flex pipe-to-
intermediate pipe
3 1 21219442 Pipe, flex 4ME22043M
4 1 21095721 Gasket, flex pipe-to-turbocharger
outlet pipe
5 1 21021852 Clamp, V-band, flex pipe-to-
turbocharger outlet pipe
6* 1 21264530 Pipe, turbocharger outlet, MP7 with 4ME33177M
2.25-degree engine mounting angle 21202658
1 21202644 Pipe, turbocharger outlet, MP7 with 4ME33176M
4.00-degree engine mounting angle
1 21202646 Pipe, turbocharger outlet, MP8 with 4ME53230M
2.25-degree engine mounting angle
1 21202648 Pipe, turbocharger outlet, MP8 with 4ME53231M
4.00-degree engine mounting angle
7 1 20978469 Ring, alignment, exhaust pipe (refer
to NOTE below)
8 1 21095721 Gasket, turbocharger outlet pipe-to-
diffuser pipe
9 1 21060426 Clamp, V-band, turbocharger pipe-to-
diffuser pipe

* Turbocharger outlet pipe part number 21264530 were implemented into production during the July 21 through August 1,
2008 timeframe. Outlet pipe part Nos. 21202644, 21202646 and 21202648 were implemented into production on May 9,
2008.

Note: An exhaust pipe alignment ring (part number 20978469, key item 7 in the table above) was implemented into

production approximately mid-October 2006. The cast diffuser and turbocharger outlet pipe include a counterbore to
accept this ring. This ring is NOT used if the cast diffuser does not include the counterbore.

Repair procedure

The correct turbocharger outlet pipe depends upon the engine model and engine mounting angle. Refer to the following
chart to determine the engine mounting angle:

Chassis Model Condition Engine Mounting Angle
CXU All tandem axles (both vendor and MACK carriers) and single 2.25 degrees
rear axle with MACK carrier
Single rear axle with vendor carrier 4.00 degrees
CHU All tandem axles (both vendor and MACK carriers) and single 2.25 degrees
rear axle with MACK carrier
Single rear axle with vendor carrier 4.00 degrees
GU All tandem axles (both vendor and MACK carriers) and single 2.25 degrees

rear axle with MACK carrier

Single rear axle with vendor carrier 4.00 degrees

When installing the exhaust flex pipe and turbocharger outlet pipe, alignment of the exhaust system must be verified as
outlined in the following steps.
Note: Alignment of the turbocharger diffuser pipe to the turbine housing, as well as alignment of the turbocharger outlet
pipe to the diffuser pipe is critical to prevent the exhaust flex pipe from cracking.

Torque specification for the V-band clamps is 6.8 Nem (60 Ib-in).

1. Verify that the alignment marks on the cast diffuser and the turbocharger turbine housing are directly opposite each
other as shown below.

Diffuser Pipe-to-Turbine Housing Alignment

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YL ae > LY | | \ \ ( \
= Ph | | | | | L | ‘
Jf he S || || | || | | !
AQ > MW | |
= Pg! tay ) | |
a md hg NI 3 ] | | |
sy —, | — * |
Las : — : NG | Is J | |
‘ \ \\ _ >) ” i } \ | | } / ‘ 4| L ,
+e] BE yy \ | ae ede
he Pt K\ JY
{ M ¢ 1] i= is Mo Le - eee get
1. Cast Diffuser 3. Diffuser Pipe-to-Turbine Housing

Alignment Marks

2. Aftertreatment Fuel Injector (AFI) 4. Turbine Housing

2. Verify that the alignment marks on the front of the turbocharger outlet pipe and the rear of the cast diffuser are
directly opposite each other as shown in the following illustration.

Turbocharger Outlet Pipe-to-Diffuser Pipe Alignment

an \ 4 |
ES a) ||
a (