ATRO offers a full line of long-lasting polyurethane replacement parts for the Hendrickson HN suspension systems. We made this video to show you key points in identifying these suspensions, along with details for maintenance, and specs for ATRO parts.

The Hendrickson HN suspension is the forerunner to the HAULMAXX® suspension. In both, the steel leaf springs of the original walking beam design are replaced by rubber or polyurethane bolster springs. Bar pin end bushings are used, but there are no center bushings for the beams to pivot on. Typical applications include dump, refuse, mixer, logging, and military.

The original HN 400/460 positioned the bolsters low inside the walking beam assembly. The HN 402/462 design brings the bolsters to a position above the walking beam. This raises the center of gravity for the suspension and can create added stress and instability. When the load is elevated overhead, for example, in a dump truck or front loader. With the bolsters positioned higher, the stress concentrates on the bond lines within the bolsters themselves.

Due to this stress concentration on bond lines, it's important to note that rubber bolsters have four plates, top and bottom endplates, and two central plates. Rubber is made of long fibers of material, so the center plates are necessary to limit the elongation of the material and provide stability against shear stresses. As a result, rubber bolsters have six surfaces to potentially suffer de-bonds.

In contrast, since ATRO's proprietary polyurethane is poured as a homogenous liquid, there is no need to add the metal center plates to limit movement. This means ATRO's bolsters are limited to just two potential de-bond areas. The higher center of gravity also puts significant stress on the transverse torque rods, and ATRO's robust torque rods and polyurethane bushings result in superior performance in these high-stress situations.

The important guidelines to remember when inspecting or replacing bolster springs are that bolsters should be replaced in pairs minimally. An important installation note, never mix ATRO with rubber or other polyurethane bolsters. Bolsters will require replacement if the material is split or cut three inches in length and one inch or more in-depth, or if a bond separation is more than one and a half inches deep.

The de-bond may be a secondary failure with separations at the top plate being related to torque rod bushing wear and separations at the bottom plate often related to the walking beam and bushing condition. Other common causes of bolster spring failure are a misalignment of the tandem axles, the outboard bracket is loose or the saddle mounting bolts are loose, the vehicle is being overloaded, or the auxiliary spring is worn.

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ATRO Suspension Schematics and Suspension Parts Lists:
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ATRO Torque Rod Finder / Quickly Find the Rod That’s Right for You:
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ATRO Field Manual / Suspensions:
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