Lower Frame Flange Cracks, Repair
M-712-004
(January 2009)

Valid for
All Mack MRU models

Case description
In certain applications, cracks may develop in the lower frame flange of the right-hand frame rail on MR model
chassis. The crack will be located underneath the outer frame bracket, just behind the front spring front hanger
bracket.
Note: Does not apply to Mack Trucks Australia.

Repair
Area Where Crack Can Occur in Frame Flange

1. Cab Tilt Hinge Bracket

4. Area Where Cracks Can Develop

2. Outer Frame Bracket

5. Front Spring Front Hanger Bracket

3. Frame Rail
Should a lower frame flange crack be encountered, the frame flange must be repaired, and the existing outer frame
bracket must be replaced. The replacement frame bracket will include four mounting holes for additional mounting
fasteners. It will be necessary to drill the four additional holes in the frame rail when replacing the outer mounting
bracket.
Outer Frame Bracket

1. Four Additional Mounting Holes in Frame Bracket

Required Parts
Part numbers for the replacement outer frame bracket are as follows:
Note: Refer to the chassis build records to determine the correct outer frame bracket.
Qty.

Part No.

Description

1

37QL4191P7

Outer frame bracket, MRU
models

37QL4191P6

Outer frame bracket, MR
models with Meritor model
636 air compressor and
power steering pump
mounted on engine timing
cover

37QL4191P5

Outer frame bracket, MR
models

4AM11 or

Pin, Huck-Spin® Metric
Frame Fastener, 16 mm,
14–26 mm grip range

4

4AM11M2

Pin, Huck-Fit® Metric Frame
Fastener, 16 mm, 15–25
mm grip range
4

159AM2

Collar, Huck® Metric Frame
Fastener, 16 mm

Procedure
1. Secure the chassis for service, apply the parking brakes and block the wheels to prevent the vehicle from
moving.
2. Disconnect the batteries by disconnecting the negative battery cable first, and then the positive cable.

3. Disconnect the harness connectors from all electronic control units (i.e., engine ECU, vehicle ECU, ABS
module, etc.)

Caution
Failure to disconnect the electronic control units or the battery cables may result in damage to sensitive
electronic components due to welding on the frame rail.
4. Tilt the cab fully forward.
5. Remove and discard the right-hand outer frame bracket.

Caution
Removing the outer frame bracket involves removing the right-side cab hinge bracket. To do this, the
cab must be properly supported to eliminate any potential for injury.
6. Drill a 1/8" hole at the end of the crack in the frame flange to stop the crack from progressing.
7. Grind the crack into a V-shape, and then fill with weld as outlined in the Frame, Axle and Suspension Service
and Total Vehicle Alignment Manual, 14–103.
8. Grind the weld smooth and then paint the welded area with a suitable chassis paint.
9. Position the replacement outer frame bracket (part no. 37QL4191P5, 37QL4191P6 or 37QL4191P7, determine
correct part number from the chassis build records).
10. Using the bracket as a template, mark the location where the four additional mounting holes must be drilled in
the frame rail.
Mark and Drill Four Additional Mounting Holes in Frame

11. Remove the bracket and drill the four 11/16″ diameter holes in the frame at the marked locations.
12. Install the replacement right-hand outer frame bracket on the frame rail. Use four Huck® pins and collars (part
no. 4AM11 for Huck-Spin® or 4AM11M2 for Huck-Fit® pins and part no. 159AM2 collars). Part numbers for all
other fasteners can be obtained from the MACKnet Parts System.
13. Cut the upper two Huck® pins flush with the collars to allow clearance for the cab tilt support bracket.
Cut Upper Huck® Pins Flush with Collar

14. Reconnect the harness connectors, which were disconnected from the electronic control units in step 3.
15. Reconnect the batteries by connecting the positive battery cable first, and then the negative cable.

Warranty information
Reimbursement
This Repair may be eligible for reimbursement if a product failure was experienced within the time and
mileage limits of the applicable warranty coverage. Reimbursement is obtained via normal claim
handling process.
Claim Type (used only when uploading from the Dealer Bus. Sys.)

01

Labor Code
Primary Labor Code

121 2G 00 80 — 6.5
hrs., Time allowed to
remove right-side
outer frame bracket,
weld-repair crack in
lower frame flange,
drill additional
mounting holes and
install replacement
bracket on MRU and
MR model chassis.
Does not include
“take-charge” time.

Causal Part

—

Issued by
Technical Service
Mack Trucks, Inc. engages in a continuous program of testing and evaluating to provide the best possible product.
Mack Trucks, Inc., however, is not committed to, or liable for updating existing chassis.