2/17/25, 4:59 PM SS 770 WST 47X/49X Dual Power Steering Gear Orific... - DTNA Solutions

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SS 770 WST 47X/49X Dual Power Steering Gear
Orifice Fittings EalS

Applicable Vehicles

Western Star 47X, 48X, 49X vehicles configured with dual power steering gears.

Symptoms

Western Star 47X/48X/49X vehicles with dual power steering gears include orifice fittings within
the power steering hydraulic fluid circuit.

For vehicles fitted with orifice fittings, the following symptoms may be observed:

e Steering effort increase when increasing speed of steering input
e Slower rate of steering wheel return-to-center from near full lock
e Most noticeable at low vehicle speed

For vehicles without orifice fittings installed in the power steering fluid circuit, the following
symptoms may be observed:

e Noticeable steering vibration, hydraulic “shudder”, or auxiliary steering gear noise/vibration
when static steering the vehicle. See attached video file as reference.

The location of the orifice fittings can be identified by the diagrams below. Set Forward Axle
vehicles have the fittings installed below the front engine cross member. Set Back Axle vehicles
have the fittings installed at the auxiliary steering gear.

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2/17/25, 4:59 PM SS 770 WST 47X/49X Dual Power Steering Gear Orific... - DTNA Solutions

Set Forward Axle Configuration

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2/17/25, 4:59 PM SS 770 WST 47X/49X Dual Power Steering Gear Orific... - DTNA Solutions

Set Back Axle Configuration

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2/17/25, 4:59 PM SS 770 WST 47X/49X Dual Power Steering Gear Orific... - DTNA Solutions

Due to variations in steering gear hydraulic assist, tolerance stack-up of steering components
and/or flowrate of power steering fluid between main and auxiliary steering gears, the above-
mentioned symptoms can be displayed on some vehicles.

An incorrect diagnosis of the reported issue can lead to unnecessary replacement of steering
components (steering gears, pumps, coolers) and extended labor hours to resolve the issue.

Solution

As the reported symptoms are dealt with on a vehicle-to-vehicle basis depending on application
and the specific symptom reported, this Service Solution serves as a troubleshooting guide to
resolve the reported issue.

The attached troubleshooting flowchart shows the relevant path to isolate the reported issue and
provides suggested solutions.

Relevant orifice fitting part numbers are:

235-14535-000 CONN-37FLARE,3/4-16,.094"0RFC
23-14535-001 CONN-37FLARE,3/4-16,.047°0RFC

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https://www.dtnasolutions.com/t5/tkb/articleprintpage/tkb-id/westernstar-service/article-id/770 4/4

Are any of these the reported
symptoms?
* Steering effort increase
when increasing speed of
steering input
* Slower rate of steering
wheel return-to-center from
near full lock
* Most noticeable at low
vehicle speed

No

Bleed
‘ hydraulic
steering No system of air
hydraulic per
circuit been Workshop
Manual

Yes

Remove orifice fittings
from hydraulic circuit and

retighten hoses.

y

Make note of the orifice
size in the fitting and the

part number

Complete the power
steering gear air bleeding
procedure per Workshop

Manual

Test drive the vehicle and
check that the symptoms
are no longer present .

Is the power
steering
performance
acceptable?

No o™

A

steering vibration,
hydraulic “shudder”,
or auxiliary steering
gear noise/vibration
when static steering
the vehicle?
See video file!

Yes

Is there a noticeable

No

Install larger
orifice
fittings into
circuit per
install
diagram

Install smaller orifice
fittings into circuit per
install diagram

Follow troubleshooting procedures to isolate front axle,
Yes steering linkage, steering shaft/column, power steering
gears, pump, fluid reservoir/filter or cooler as the cause
of symptom?

A