Hendrickson Trailer Parts Catalog

ZMD ® Frequently Asked Questions


10. Is ZMD ® technology compatible with lift kits or lift systems? ULTRAA-K ® UTKNT 40K and VANTRAAX ® HKANT 40K suspensions equipped with ZMD technology are incompatible with Hendrickson lift systems. INTRAAX ® AANT and AAT 23K / 25K suspensions equipped with ZMD technology are compatible with Hendrickson’s recommended lift kits. Refer to Hendrickson Literature Number L801 Liftable Application Guide for more

information on lift kit availability for AANT 23K and AAT 23K / 25K suspensions. 11. Is ZMD technology compatible with RCA Raised-Center Axles?

INTRAAX AAT 23K / 25K suspensions equipped with ZMD are compatible with RCA. AAT 23K / 25K models specified with standard travel and 14-inch through 17-inch ride heights are available. AAT 23K / 25K models specified with limited rebound travel and 14-inch or 16-inch ride heights are available. RCA is recommended with limited rebound travel. 12. Are replacement ZMD air springs available in the aftermarket? YES. ZMD air springs and down stops are available in the aftermarket. Contact your Hendrickson Customer Service Representative for more details. 13. Why is ZMD limited to specific ride heights on ULTRAA-K, HKANT 40K and select top-mount INTRAAX models? ZMD is currently limited because this patented air spring is rated for 20K axle applications. Additionally, the down stop has been rigorously tested for these specific applications. 14. How are ZMD air springs installed? ZMD air spring installation procedures and mounting hardware are identical to standard air spring and shock installation procedures. To install ZMD air springs as a retrofit, simply remove the existing shocks and air springs and replace with ZMD air springs and down stops. The select INTRAAX AANT 23K models that are available with ZMD require an additional bolt to be added to the shock clevis on winged hangers only. Follow all applicable Hendrickson installation, service, maintenance and repair procedure publications. 15. Can standard air springs be mixed with ZMD air springs? NO. Mixing ZMD air springs with standard air springs is not recommended.While the load curves for each product are somewhat similar, they provide different damping performance to the suspension system. Mixing ZMD and standard air springs on the same suspension can adversely affect the operation and life of other integral suspension components. 16. Can ZMD air springs equipped on VANTRAAX ® and INTRAAX suspensions be interchanged? NO. Both ZMD and standard air springs are specially designed to meet the needs and geometry of the specific application. It is important to use only the exact air springs specified by Hendrickson for each model to ensure maximum operation performance and life of components. 17. How can customers tell the difference between a ZMD air spring and a standard air spring? The customer must visually inspect the air spring to verify the type of air spring. Identifiers include: • ZMD embossed on the bellows • Part number • Down stop instead of shocks Similar to today’s standard air springs, the Hendrickson part number will be located on the ZMD air spring bellows. 18. Is there slack in the down stop on ZMD? • Sealed piston bottom • Black plastic on ULTRAA-K

YES. There is slack in the down stop to allow 3 to 4 inches of suspension travel on ULTRAA-K ® and VANTRAAX HKANT 40K models. The select top-mount INTRAAX models available with ZMD will allow for 2 inches of suspension travel. 19. Will the down stop kink or twist? The down stop cover helps prevent the down stop from twisting and kinking at installation and while the trailer is in service.



Refer to Hendrickson Literature No. L1212 - ZMD ® Zero Maintenance Damping ® FAQ Brochure

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