Parking brake cable had pulled loose from the clip that holds it to the rear axle, allowing it to wear against the rear shock absorber. This caused a weak spot in the rubber boot that holds compressed air for the load levelling function. This caused the boot to rupture as the vehicle was being loaded, and the load levelling system was pumping up the shocks. Since this was an ongoing wear process, it could have caused a failure at highway speed with the vehicle heavily loaded, causing a loss of control to the vehicle. Poor fitup between the cable and the axle mounts appears to be a contributing factor, as it springs the cable in a direction that may cause the separation from its clip.

- Boxford, MA, USA