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REAR AXLE

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Title : Suspension Lean Diagnostics
Applies To : All Vehicles

Change Log
Dealers: Please refer to the change log text box below for recent changes to this article:
09/09/2034 - Updated article with MV & HV parts
07/15/2018 - Added new information to include CV Model units, also added a note that changing seats and plates can effect driveline
angles, so measurements need to be taken.
11/06/2018 - Reassigning to different owner
06/09/2016 - Information added about induced leans under the "CAUTION:" tab.
12/14/2015 - Part number change to show correct shim thickness.

Description
This article addresses chassis lean conditions on all chassis. This does not include any diagnostics for body leans such as a
cab lean. Keep in mind that a chassis lean may cause or accentuate a cab lean. Filling out the printable form and using the
notes in blue will help you to determine the source of the lean and identify the action and parts required to correct the lean.
If you are not able to come to a repair direction after completely following the article and filling out the form, please attach
the form and requested photos to a case file for further assistance.
For any lean issues with a front suspension rating of 8,000 LBS or less please refer to IK0300061 - 8,000 LBS Front
Suspension Lean Correction.
Some trucks are intentionally manufactured with different front axle spring rates on the driver and passenger sides. The
Parts Catalog will illustrate this. Many MV's have this design feature.
If a chassis has a front lean complaint of less than 1/2 inch, AND there is no body installed, AND the parts catalog
shows that it has different part number springs on front drivers side versus front passenger side, then DO NOT
troubleshoot the lean until the body is installed or significant weight is installed on the chassis
IROS 4x2 chassis require the most measurements. A front shim, rear seat or frame issue are the possible repair paths
depending on the measurements in all steps of the diagnostic form. It is critical to take accurate measurements for all
steps to determine if the issue is being caused by the rear suspension.
IROS 6x4 diagnostics does not include the pin bar height measurement. This is due to 4 points of contact to the
frame for the rear suspension. Changing rear seats in an IROS equipped 6x4 will have minimal impact on a chassis
lean.

Other air suspensions designs do not allow the rear suspension to impact a front lean the way an IROS suspension can.
As a result it has been found that a front shim or frame issue are the most common repair practices based on the results
of the measurements.
Vari-Rate rear spring suspension can be shimmed in the front or rear to correct a lean. A shim or a frame repair are the
most common repair practices based on the results of the measurements.
If you are unable to resolve the lean after completely following the iKNow article, please open a case file with the
form completely filled out. Attach the form and the 4 requested photos to the case file.
CAUTION :
Shimming is not an acceptable practice for chassis lean created by the addition of auxiliary equipment or loading
practices resulting in vehicle lean. These procedures are intended to assist the service technician in making industry
acceptable corrections for nominal lean issues and are not intended to compensate for over/uneven loading or unrepaired vehicle damage - regardless of cause.
There is an orderable option that will in fact create a lean for a purpose to compensate a heavy body install (Cement
Mixers, Snow Plows). If the unit is leaning, refer to the component section of the unit in Service Portal. This feature is
added for most DuraStars with 8k front ends with batteries, DEF tank, Air Tanks, and Fuel Tank all on the Left side.
0003WAM - Typically a 1" spacer is installed on the Front Left.
0503013 - May be built with different rate springs on left versus right or a 1/2" spacer is installed on the Front Left.
NOTE:
On an air ride suspension, replacing the air spring or the MSM (main support member, aka – rear spring) will not have
any effect on lean.
Warranty will NOT COVER replacing a spring for the following complaints:
Weak spring

Leaning

Bottoming out

Lost arch

Service Parts Information
Springs are very rarely found to be the cause of a lean. As a result, the most common springs that are replaced with no
issue found upon review have been listed at the bottom of this article. To review the spring information CLICK HERE
Figure

Kit Description

Part Number

Quantity
Required

Notes

1

3 Inch Wide x 1/2 Inch Thick Front Spacer (has
center dowel in it)

2512808C1

1

As Needed

2

4 Inch Wide x 5.8 x 1/8 Inch Thick Front Spacer

442078C2

1

As Needed

2

4 Inch Wide x 5.8 x 3/8 Inch Thick Front Spacer

322019C4

1

As Needed

2

4 Inch Wide x 8.8 x 1/8 Inch Thick Front Spacer

442388C1

1

As Needed

2

4 Inch Wide x 8.8 x 3/8 Inch Thick Front Spacer

1618382C1

1

As Needed

3

4 Inch Wide x 1/4 Inch Thick Rear Spacer

493720C3

1

As Needed

3

4 Inch Wide x 3/8 Inch Thick Rear Spacer

540069C3

1

As Needed

3

4 Inch Wide x 1/2 Inch Thick Rear Spacer

493721C3

1

As Needed

500871c2 = 1 inch spacer, 3956545c2= 2 inch
spacer, 3894346c2= 1.5 inch spacer

Figure 1

Figure 2

Figure 3

Diagnostic Steps
The diagnostic steps vary based on suspension type.
The locations the chassis should be measured are the same on all types of suspensions.
This will allow for the most accurate results.
Proper locations to measure for chassis lean (All suspension types).
Figure 4
Right Front Spring Shackle Bolt

Figure 5

Left Front Spring Shackle Bolt

Figure 6
Aft Frame Straight Truck

Figure 7
Aft Frame Tractor

Clicking the links below will open a printable form in a new window and jump to the appropriate section of this iKNow
article.
Printable Form

IROS Suspension

Click Here

Other Air Suspension

Click Here

Vari-Rate Suspension

Click Here

IROS Suspension
1. Check front axle suspension weight rating.
For any lean issues with a front suspension rating of 8,000 LBS or less please refer to IK0300061 - 8,000 LBS Front
Suspension Lean Correction.
2. Check the unit for any offset loading.
Note any items that may cause offset loading.
If offset loading is present advise non-warrantable cause. Advise installing 14WAS – Dual leveling valves to correct
issue.
3. Inspect the suspension for any third party (bodybuilder) installed components such as stabilizer bars.
International does not install stabilizer bars on most suspensions.
Exceptions: BE Buses, Front suspension on CityStars, and the Multi-Link front air suspension (These will have
stabilizer bars).
Advise non-warrantable to remove components. Recommend removal of components to confirm they are causing
the lean.
Also, a 3rd party component could be an item causing an offset load. Keep that in mind.

4. Check the tire pressure for all tires.
Adjust pressures if needed.
Record current tire pressures.
It is recommended each axle be with 5% of each other. Especially if the lean is marginal.
5. Verify ride height is properly set per instructions below.
Park the vehicle unloaded on a level surface with a light application of the brakes.
Do not apply the parking brake. Chock wheels to prevent vehicle movement.
Make sure 120 psi is in the vehicle air system, and then shut off engine.
Dump air from system, then re-pressurize and allow it to return to the ride height.
Measurements are taken at the air spring assembly closest to the height control valve (usually forward left).
Measure the vertical distance from the bottom of the straight edge that is resting against the u-bolts, to the
bottommost position of the axle stop.
There should be no angle created between the two measurement points.
Figure 8

If you're outside the listed values on the table below, the height control valve will need to be adjusted. If
adjustment is needed CLICK HERE
IROS Suspension Height Adjustment Specification Chart
IROS Suspension Feature Code

Config

Model

Axle Travel in Inches
(measured from axle stop,
see Figure 2)

14UNN, 14UNM, 14UNL, 14UNS,
14UNT, 14UNU

6x4

All

2.75 ± 0.125 or 2 3/4 ± 1/8

14TBJ

4x2

7000, 8000, 9000

2.75 ± 0.125 or 2 3/4 ± 1/8

14TBJ, 14TBG, 14TBH, 14TBK,
14TBR, 14TBS, 14TBT
NOTE: For 14TBS, 14TBT Verify
Model

4x2

3200, 4000. CE 200, CE
300, FE 300

3.0 ± 0.125 or 3 ± 1/8

NOTE: Above Codes are not with
14WAW

14WAW (Flat Floor)

4x2

2.7 ± 0.125 or 2 11/16 ±

3000

1/

8

14TBS, 14TBT
NOTE: For 14TBS, 14TBT Verify
Model

4x2

RE 200, RE 300

14TBL, 14TBM, 14TBN
NOTE: Verify Build Date

14UNH

4x2

6x4

4000

9000

2.375 ± 0.125 or 2 3/8 ±
1/

8

4.6 ± 0.125 or 4 5/8 ± 1/8
Models built before
02/23/2004
3.2 ± 0.125 or 3 3/16 ± 1/8
Models built starting
02/23/2004
1.55 ± 0.125 or 1 9/16 ±
1/

8

14TBY

4x4

CXT, 7000

3.1 ± 0.125 or 3 3/32 ± 1/8

14TCH

4x2

TerraStar

3.0 ± 0.125 or 3 ± 1/8

14TCP, 14TCR

4x2

AE Bus

3.0 ± 0.125 or 3 ± 1/8

All dimensions are in inches

6. Once the proper ride height is set, and air bags are inflated with 120 psi, measure each corner of the vehicle as shown in
Figures 4-7 and record measurements.
The front tires MUST be pointed straight forward to prevent any influence to the lean from King Pin Inclination.
Measure the front suspension at the spring shackle bolt as shown in Figures 4 and 5. Mark the bolt with a paint
pen so you have a reference point for future measurements that may be required.
Measure the rear of the vehicle at the aft frame flange (bottom of the flange) as shown in Figures 6 and 7. Location
may vary slightly by application.
If the lean is less than or equal to 3/8” Front and/or Rear, the vehicle is in spec. The repair is not warrantable.
You can still advise on what repair would correct the lean, but at customer pay.