Technical
Procedure

Trailer Suspension Systems

ZMD® ZERO MAINTENANCE DAMPING®

SUBJECT: INTRAAX®/VANTRAAX® Retrofit Kit
Installation Procedures
LIT NO: T81001 
DATE: October 2018
REVISION: D

TABLE OF CONTENTS

Important Safety Notices........................................................................................................................ 1
Introduction........................................................................................................................................... 1
Remove Original Components................................................................................................................. 2
ZMD® Down Stop................................................................................................................................... 2
Installing Self-tapping Reinforcement Bolt..................................................................................................... 2
Installing ZMD® Down Stop........................................................................................................................... 2
Installing ZMD® Air Spring..................................................................................................................... 3
Appendix A: Lower Mount Repair, if required.......................................................................................... 4
Down stop

ZMD®
air springs

Down stop

INTRAAX®

VANTRAAX®

Figure 1: ZMD installed on INTRAAX and VANTRAAX suspensions

IMPORTANT SAFETY NOTICES

Hendrickson literature number T12007 Technical
Procedure General Safety Precautions and Information,
available at www.Hendrickson-intl.com/TrailerLit,
includes important preparation, precautionary and
safety information pertaining to the procedures
included in this document. Warnings, cautions and
other relative statements included in T12007 should
be read carefully to help prevent personal injury and
equipment damage.
Improper maintenance, service or repair can cause
damage to the vehicle and other property, personal
injury, unsafe operating conditions and potentially void
the manufacturer’s warranty.

INTRODUCTION

ZMD® ZERO MAINTENANCE DAMPING® Technology
includes two major components: ZMD air springs and
down stops (Figure 1). DO NOT mix ZMD air springs
with standard air springs on a trailer. Retrofit kits1 are
currently available for select VANTRAAX® and INTRAAX®
models.
To install the retrofit kit, use the procedures in this
document and installation drawing D-25266 2 Common
Component Installations.

1

2

Refer to L1073 or L1074 for applicable OEM unassembled installation
drawings.
Installation drawing D-25266 is provided with each ZMD down stop and
available online at www.Hendrickson-intl.com/TrailerLit. Where duplication
exists, refer to the installation drawing.

INTRAAX®/VANTRAAX® RETROFIT KIT Installation Procedures
REMOVE ORIGINAL COMPONENTS

Install the self-tapping reinforcement bolt, provided with
the kit1, as follows:

During this procedure, original air springs and shocks
must first be removed from the suspension or slider.

1.

1. Support trailer at the ride height position.

Verify the self-tapping bolt is not present (Figure 2).

If present, it is not necessary to replace the bolt.
Continue with INSTALLING ZMD® DOWN STOP.

2. Exhaust air from air springs.
2.

Insert the self-tapping bolt into the upper clevis hole, as
shown in Figure 2.

3.

Ensure the bolt head is fully seated against the clevis.

4. Remove existing air springs and shocks.

4.

5. Discard the original air springs, shocks and
mounting hardware.

To avoid cross threading, thread the nut onto the selftapping bolt two full turns, by hand.

5.

Tighten the lock nut to a torque of 25 ft. lbs. (34 Nm).

ZMD® DOWN STOP

After the reinforcement self-tapping bolt is installed, the
ZMD down stop can be installed in the next procedure.

3. Disconnect air spring air lines and remove fittings
(unless damaged or unusable, do not discard
fittings)

Installation of ZMD down stops is identical to installing
standard shock absorbers on INTRAAX® suspensions or
VANTRAAX® sliders. However, INTRAAX suspensions with
winged frame brackets require a reinforcement bolt.

INSTALLING ZMD® DOWN STOP
The ZMD down stop is installed using existing upper
and lower mount locations (Figure 4 and Figure 5) and
the hardware provided with the kit.

INSTALLING SELF-TAPPING REINFORCEMENT BOLT
This procedure is only required for INTRAAX AANT 23K
suspensions with winged frame brackets (Figure 2). For
INTRAAX suspensions with wingless frame brackets (Figure 3),
a gusset in front of the wing provides adequate upper clevis
support.

Upper clevis
ZMD down stop

NOTICE: DO NOT install self-tapping reinforcement
bolt on VANTRAAX or INTRAAX AAT 23K
suspensions.

Lower mount
with sheartype bolt

Lower mount
lock nut, tacked
to inside of
suspension beam

Nut

Lower air spring
mounting stud
and lock nut

Self-tapping bolt
Upper clevis
Frame bracket
View looking outward

Rear view

Air spring
INTRAAX (shown upside down)

Figure 2: INTRAAX winged frame bracket requiring upper clevis
reinforcement bolt

Spacer
Hardened washers (x2)
Shear-type bolt

Gusset

(Do not reuse)

Down stop
3
/4-10
lock nut

Upper clevis
Rear view

Upper
clevis
3

View looking outward

Figure 3: INTRAAX wingless frame bracket

/4-10 x 3.5"
hex bolt

VANTRAAX (shown upside down)

Figure 4: ZMD down stop mounting to existing shock mounts
®

NOTICE: Failure to follow these instructions
could result in damage to the
suspension and/or its components.

1

2

Refer to D-28108 for installing self-tapping bolt on unassembled INTRAAX
suspensions.
T81001 D

INTRAAX®/VANTRAAX® RETROFIT KIT Installation Procedures
INSTALLING ZMD® AIR SPRING

Replace the original air springs with the ZMD air springs
and hardware provided with the kit.
1. Install replacement ZMD air spring using
replacement top and bottom hardware.
2. Tighten the lower air spring lock nut (Figure 4) to a
torque of 58±2 ft. lbs. (79±2 Nm).

Upper clevis
Down stop

3. Tighten the upper air spring nuts to a torque of
90±10 ft. lbs. (125±10 Nm).

Lower
mount
Figure 5: ZMD® down stop connection (VANTRAAX® shown)

4. Reconnect air line fittings and hoses to the air
spring.

1. Install one eyelet of the down stop in the upper
clevis (Figure 4) using the 3/4-10 x 3.5 hex bolt and
lock nut provided with the kit.

5. Repeat this procedure for the other original air
springs on the trailer.
6. Return trailer to normal operating state.

2. Tighten to a torque of 225±10 ft. lbs. (300±10 Nm).

7. Check for air leaks.

3. Using the hardware provided with the kit, slide
a hardened washer onto the shear-type bolt
(Figure 4).

8. Refer to L459 to ensure the trailer is at proper ride
height.

4. Insert the shear-type bolt through the lower eyelet
of the down stop.

For assistance in the United States and Canada, call
Hendrickson Trailer Technical Services at 866‑RIDEAIR
(743‑3247) or email HTTS@Hendrickson-intl.com.

5. Slide the second hardened washer onto the sheartype bolt.
6. Thread the shear-type bolt into the lower mount nut
as shown in (Figure 4) and hand tighten.
NOTE: For the suspension beam lower mount, the
nut is tack welded inside the beam (Figure 4).
If the threads are damaged and the nut is not
reusable, refer to APPENDIX A: LOWER MOUNT
REPAIR, IF REQUIRED on page 4.

Figure 6: Shear bolt Torx head separation

7. Use an E20 Torx® socket to tighten the shear-type
bolt until the bolt’s Torx head shears off, as shown in
Figure 6.
8. Repeat this procedure for the other frame brackets
and suspension beams on the trailer.

T81001 D

3

Appendix A: LOWER MOUNT REPAIR, IF REQUIRED

If the nut on the inside of the suspension beam, lower mount, is damaged or cannot be reused (i.e., threads
are stripped, nut is cracked, etc.); drill out the threads in the lower mounting block inside the suspension beam
(Figure 7) and use the extra washer and nut provided in the hardware kit to complete the lower mount.
Drill out
these threads
with 3/4" bit

Before drilling

After drilling

Hardened washer
3

/4"-10 Hex nut

NOTE: Washer and nut are
placed on top of
existing mounting
after drilling.
Figure 7: Damaged thread hardware assembly for lower mounting bolt

For more details relative to this repair, refer to L635 provided with the kit and available at
www.Hendrickson-intl.com/TrailerLit.

Call Hendrickson at 866.RIDEAIR (743.3247) for additional information.
TRAILER COMMERCIAL VEHICLE SYSTEMS
2070 Industrial Place SE
Canton, OH 44707-2641 USA
866.RIDEAIR (743.3247)
330.489.0045 • Fax 800.696.4416

www.hendrickson-intl.com
T81001 Rev D 10-18 ECN 31426

Rev C 07-18 ECN 31427

Rev B 09-16 ECN 25587

Rev A 12-14 ECN 23613

Hendrickson Canada
250 Chrysler Drive, Unit #3
Brampton, ON Canada L6S 6B6
800.668.5360
905.789.1030 • Fax 905.789.1033

Hendrickson Mexicana
Circuito El Marqués Sur #29
Parque Industrial El Marqués
Pob. El Colorado, Municipio El Marqués,
Querétaro, México C.P. 76246
+52 (442) 296.3600 • Fax +52 (442) 296.3601

04-13 ECN 21817

Information contained in this literature was accurate at the time of publication. Product changes may have been made after the copyright date that are not reflected.

© 2018 Hendrickson USA, L.L.C. All Rights Reserved

Printed in United States of America