IK0300071 - Non-IROS Rear Air Suspension Ride Height Specifications and Adjustment... Page 1 of 6

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SPRINGS AND SUSPENSION

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12/12/2018

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Title : Non-IROS Rear Air Suspension Ride Height Specifications and Adjustment Procedures
Applies To : All Vehicles

CHANGE LOG
Please refer to the change log text box below for recent changes to this article:
12/17/2018 - Removed CV from vehicle list
12/17/2018 - Initial Article Release

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DESCRIPTION
This document will guide the user to determine the correct ride height specifications for non-IROS rear air suspensions for single,
tandem and tridem axle configurations. The ride height measurement is often required for a variety of different diagnostics. Truck
specific ride height procedures can be found on the truck's service manual. If this information is not included in the truck's service
manual, please refer to the instructions in this article.

SYMPTOM(s)
Not Applicable

SPECIAL TOOL(s) / SOFTWARE
- Measuring Tape
- Marker Pen

SERVICE PARTS INFORMATION

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IK0300071 - Non-IROS Rear Air Suspension Ride Height Specifications and Adjustment... Page 2 of 6

Not Applicable

DIAGNOSTIC STEP(s)

Step Action
DIAGNOSTIC: Can the ride height be measured following the truck's service
manual based on the specific air suspension feature code ride height
specifications?

Yes. Proceed to Step 2

No. The information is not included in the
truck's service manual.
Proceed to the "Ride Height Measurement
and Adjustment procedure" within this
iKnow article.

1

Step Action
2

Decision

Decision

DIAGNOSTIC: Is the ride height adjustment instructions in the truck's service 1. Yes. If the ride height does not meet
manual?
the specifications, please proceed with
adjusting the vehicle's ride height
following the manual's procedure.
2. No. The information is not included in
the truck's service manual. Proceed to the
"Ride Height Measurement and
Adjustment procedure" within this iKnow
article.

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Ride Height Measurement Procedure
IMPORTANT: It is very important that the height valve be cycled completely before and after any ride height adjustments.
Cycling of the height valve will help make the adjustment more accurate.
1. With air system pressure over 100 psi, deflate rear suspension to lowest level.
2. Re-inflate rear suspension allowing it to return to ride height with air system pressure over 100 psi.

Figure 1: Axle tube front center line
Item 1: Axle tube front vertical measurement
Item 2: Axle tube center line mark
Item 3: Axle tube

3. At wheel end of axle tube (3), closest to leveling valve, measure vertically on front of axle tube (1) and find the center of the axle
tube. See figure 1.
4. Mark a line on the front of the axle tube indicating the center measurement of the axle tube (2). See Figure 1.

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IK0300071 - Non-IROS Rear Air Suspension Ride Height Specifications and Adjustment... Page 4 of 6

Figure 2: Axle tube rear center line
Item 1: Axle tube center line mark
Item 2: Axle tube rear vertical measurement
Item 3: Axle tube

5. At same wheel end of axle tube (3), measure vertically on the rear of the axle tube (2) and find the center of the axle tube. See
Figure 2.
6. Mark a line on the rear of the axle tube indicating the center measurement of the axle tube (1). See Figure 2.

Figure 3: Ride Height Measurement
Item 1: Bottom of frame rail
Item 2: Marked line on front of axle tube
Item 3: True center of axle tube
Item 4: Marked line on rear of axle tube

7. Measure vertical distance from marked line on front of axle tube (2) to bottom of frame rail (1). See figure 3. Record measurement.
8. Measure vertical distance from marked line on rear of axle tube (4) to bottom of frame rail (1). See Figure 3. Record measurement.

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9. Average recorded measurements made from front and rear of axle tube. Averaged measurement will indicate proper ride height from
true center of axle tube (3) to bottom of frame rail (1).
10. Ensure measurement average reads the same as stated in the Feature Code description (see Table 1.
11. If measurements are out of specification, perform follow-on procedure to make necessary adjustments.

Table 1: Non-IROS Ride Height Specification by Air Suspension Feature Code
Single Axle Rear Air suspension
Hendrickson Air Suspension (HAS)
Feature Code Ride Height (bottom of frame to center of wheel)
14TAX
9.5 ±1/8"
14TAY
10.6 ±1/8"
Hendrickson Primaax HS (PAX)
Feature Code Ride Height (bottom of frame to center of wheel)
14TBZ
9.0 ±1/8"
14TCJ
13.0 ±1/8"
14TCL
9.0 ±1/8"
14TCZ
13.0 ±1/8"
Tandem Axle Rear Air suspension
Hendrickson Air Suspensions (HAS)
Feature Code Ride Height (bottom of frame to center of wheel)
14UKZ
9.5 ±1/8"
14ULA
9.5 ±1/8"
14ULU
9.5 ±1/8"
14ULV
9.5 ±1/8"
14XAL
10.6 ±1/8"
14ULB
9.5 ±1/8"
14ULC
9.5 ±1/8"
14ULS
9.5 ±1/8"
14ULT
9.5 ±1/8"
14XAM
10.6 ±1/8"
Hendrickson Primaax EX Air Suspensions
Feature Code Ride Height (bottom of frame to center of wheel)
14UNW
9.0 ±1/8"
14UPS
13.0 ±1/8"
14UNX
9.0 ±1/8"
14UNY
9.0 ±1/8"
14UPU
10.0 ±1/8"
14UPV
9.0 ±1/8"
14UPW
9.0 ±1/8"
14UPX
10.0 ±1/8"
14UPL
10.5 ±1/8"
Hendrickson HTB Air Suspensions
Feature Code Ride Height (bottom of frame to center of wheel)
14UNV
9.25 ±1/8"
Raydan Air Link™ Suspensions
Feature Code Ride Height (bottom of frame to center of wheel)
14VKL
10.5 ±1/8"
Tridem Axle Rear Air suspension
Hendrickson Primaax Air Suspensions
Feature Code Ride Height (bottom of frame to center of wheel)
14UPC
9.5 ±1/8"
14UPP
12.5 ±1/8"

Ride Height Adjustment Procedure
IMPORTANT: It is very important that the height valve be cycled completely before and after any ride height adjustments.
Cycling of the height valve will help make the adjustment more accurate.
For Ride Height Specifications, please refer to Table 1.
If travel exceeds specification:
1. Do not bend height control system brackets or rods to adjust suspension height.

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IK0300071 - Non-IROS Rear Air Suspension Ride Height Specifications and Adjustment... Page 6 of 6

2. Loosen lever arm bolt that holds arm to height control valve.
3. Pivot lever arm down to exhaust air from suspension, lowering chassis to some point below correct air ride spring height.
4. Final air ride spring height must be achieved by adding air to suspension, not exhausting.
5. Add air until axle travel reaches proper value according to specifications table.
6. When correct axle travel value has been achieved, retighten lever arm bolt.
If travel is less than specification:
1. Do not bend height control system brackets or rods to adjust suspension height.
2. Loosen lever arm bolt that holds arm to height control valve.
3. Push lever arm up to add air to suspension, raising chassis, until axle travel reaches proper value according to specifications table.
4. When correct axle travel value has been achieved, retighten lever arm bolt.

WARRANTY INFORMATION
Warranty Claim Coding:
Refer to the Warranty Coding Manual for Group and Noun Codes.

Standard Repair Time(s):
Refer to the SRT Manual for Repair Times

OTHER RESOURCES
Master Service Information Site

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