Solution K28501552
Friday, March 27, 2020 4:07:11 PM CET

** SOLUTION **
Title

Mack Chassis - Models GU / GR, CHU, CXU, AN - Constant Correction To Center

Mack Models
Mack Model

AN - Anthem , CHU - Pinnacle, Axle back , CXU - Pinnacle, Axle front , GU - Granite

Emission Standard
Emission Standard

US10+OBD13 , US14 , US14+OBD15 , US14+OBD16 , US14 CNG , US17 , US17+
OBD16

Engine family
Engine family

MP7 , MP8 , MP10

** SOLUTION **
Cause

There have been reports of certain Mack Trucks - Models GU / GR experiencing
Constant Correction To Center.

Solution

GU/GR, CHU, CXU, AN Constant Correction To Center
Often times perceived as riding on a cam lobe and having to correct the steering
wheel back to center or not holding a true line.

Vehicle Checks
(CHECKS MUST BE PERFORMED 1ST)
Tire design and pressure.
All tire pressures should be reduced to 80lbs.-90lbs. and vehicle driven,
bobtail, as a test.
Tire damage, uneven or extreme tread wear or mismatched tires/sizes.
High tread block tires (ex. Bridgestone 426EL) may ride on the center sip
of the tire causing the truck to drive from the ‘rear’ causing a need to
constantly correct with the steering wheel.
If vehicle has a 5th wheel, is it lubed properly, does wandering only happen with
a trailer?
Basic alignment specs i.e. toe, thrust line and caster.
Turning torque at the steering wheel nut, depending on surface area tested on,
tires pressures, etc. avg. 60-75in lbs. or less.
Diagnosis can be completed by breaking the system into smaller sections
(upper vs. lower, etc.).
Looseness or binding in the following components:
Steering wheel or steering column
U-joints or slip joints in upper steering system
Steering gear (diagnose per manufacturer’s specifications i.e. flow
/pressure)
Pitman arm
Draglink ends and adjustment areas
Kingpins/bushings

Tie rod ends
Spindles
Wheel bearings
Lug nuts
Springs/spring hanger brackets
Front and rear axles and u-bolts
Steering box mounting, miss mounting may result in distortion of gear

GU Alternate Cab Wall Boot
For GU vehicles produced prior to 1st week of January 2017. A change of the
upper steering column happened in November of 2014 (4mm shorter). With this
change we believe an interference may be present with the column boot on the
cab wall. This may create undue pressure on the column shaft as it comes out of
the cab wall.

Pressure from the boot may be applied to the steering column shaft restricting it
from turning freely. To check, disconnect upper steering shaft at base of column
shaft. Remove boot (there may be a noticeable movement upward of the shaft).
Reassemble steering shaft to steering column and test drive. If problem is
resolved replace boot with 84723313 (Introduced into production 2017w01).
Test drive after boot replacement to ensure problem is resolved before returning
truck to customer.

GU / GR Without Assist Gear - Alternate Steering Gear/Shaft Configuration
An e-service case to Reliability must be submitted with results of previous
checks prior to installation of gear and shaft.
On non-assist gear trucks we have a steering gear from Sheppard with a 90°
miter box on top. This can be used with an Anthem 1 piece steering shaft.
Sheppard steering gear part # 8148-SD110PAE3.
Steering shaft 84703023 x 1.
Screw 25106380 x 2.

Nut 25098472 x 2.
Follow Impact service procedures for gear and shaft replacement.
Clearance to any component must be a minimum of 1”.
Pillow block bearing bracket may be left in place and trimmed off or not.
Slightly stiffer steering may result. May improve as components wear in.
Use 84734967 as the causal part in the claim.

Solution visibility

Dealer distribution

Function(s)/component(s) affected
Function affected

steering , tires/wheels

Function Group
Function Group

641 steering wheel, column lock, steering column, shaft

Customer effect
Main customer effect

Poor straight-line directional stability , diagnostics/methodology , efficiency/abnormal
behavior

Road behaviour

driveability

Conditions
Vehicle operating mode
Frequency of occurrence of
problem

when driving , cornering
always

Administration
Author

RU1991v

Last modified by

A241298

Creation date

21-02-2017 22:02

Date of last update

24-03-2020 19:03

Status

Published

Average score

0

Number of scores

1

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