Hendrickson HAULMAAX

HAULMAAX was the evolution of HN that brought lower costs and lighter weight. It also brought the “virtual center point” down. HAULMAAX has the bolsters down the side, as opposed to HN bolsters on top of the beam. This was important for high center of gravity vehicles. This made the HAULMAAX much more roll stable than the HN for these applications. 

Hendrickson upgraded the HAULMAAX with the PLS (Progressive Load Spring) about in 2013. This eliminated the need for the frequent maintenance of shimming (you still need to check the shims because they will still wear over time), as it eliminated the strike through events. When a truck flies over the intersection or crown of the road the suspension will “slap” down (the auxiliary spring striking the shim plates) creating a jarring event, and potentially a strike through.

The PLS is engaged at all times (unloaded and loaded). In the unloaded state, it provides a smooth rate curve – meaning a nice spring rate for a comfortable ride. As the truck is loaded, the PLS will compress into the second state providing high roll stability. Because the PLS is always engaged, this also protects the bolster springs because it shares in carrying the load, resulting in longer bolster life. 

Many people don’t change out the auxiliary spring or PLS when below 3 inches in the free state. This leads to all of the load getting carried on the bolsters which leads to premature failures – or short bolster life. Refer to the maintenance schedule.

This suspension is meant to be in tension. There are a set of straps, previously on the inboard side of the bolster center, now outboard as standard. These are not the double-rebound straps. If your vehicle will ever be elevated like in a crane using outriggers, or potentially even towed, these extra straps (double-rebound) are needed to keep the suspension from dropping away from the vehicle. This means an additional set of straps should be used on both sides of the suspension.