Manlift Rollaway Incident and Drive System Recovery

[MikePhua]

The Simon Trailblazer and Its Evolution into Terex
The Simon Trailblazer series, later absorbed into the Terex aerial lift family, was designed for rugged jobsite mobility and elevated work access. These machines featured four-wheel drive, hydraulic outriggers, and platform heights ranging from 40 to 60 feet. By the late 1990s, Simon had become a recognized name in the aerial lift market, particularly in North America. After Terex acquired Simon, the Trailblazer models were gradually integrated into Terex’s broader product line, though many units remain in service today.
The Trailblazer 40, a mid-sized manlift, was equipped with hydraulic travel motors, fail-safe braking systems, and diesel engines from various suppliers—including Isuzu, Perkins, and Continental. These machines were built for reliability, but like all aging equipment, they require careful attention to hydraulic integrity and brake function.
Incident Overview and Immediate Symptoms
In one case, a Trailblazer 40 was parked on a slight slope after returning from a jobsite. Overnight, it rolled approximately 60–70 yards down a hill, despite being powered off. The next day, the machine could move on flat ground but failed to climb inclines. Eventually, it stopped moving altogether, though all other functions—boom lift, rotation, and engine—remained operational.
This behavior points to a failure in the drive system, most likely involving the rear axle brakes or travel motor. The machine’s front wheel motors were already non-functional, leaving the rear axle as the sole source of propulsion.
Terminology Annotation

• Travel Motor: A hydraulic motor that drives the wheels or tracks of mobile equipment.
  
• Fail-Safe Brake: A spring-applied, hydraulically released brake system that engages automatically when hydraulic pressure is lost.
  
• Planetary Hub: A gear reduction unit mounted at the wheel, increasing torque and reducing speed.
  
• Yoke Coupling: A mechanical connector between the motor shaft and the hub input shaft.
  

Brake System Design and Failure Modes
The Trailblazer 40 uses hydraulic disc brakes mounted on the rear axle, with fail-safe actuators that apply braking force when hydraulic pressure is absent. For the machine to roll freely downhill, both brake units would have to fail simultaneously or be improperly adjusted.
Possible failure modes include:

• Broken Belleville washers inside the brake assembly
  
• Worn or misadjusted brake disks
  
• Hydraulic contamination or water ingress
  
• Rusted or seized actuator components
  

A retired electrician who owned the machine noted that the hydraulic fluid had previously contained significant water, which he had flushed. However, residual moisture may have compromised seals or corroded internal brake components.
Diagnostic Steps and Field Testing
To isolate the issue, the owner jacked up the rear axle and ran the travel motor. The wheels rotated freely, and the brakes appeared to engage when the drive control was released. However, on a 10% grade, the machine slowly rolled backward when stationary—indicating insufficient brake holding force.
Recommended diagnostic steps:

• Inspect brake actuator housings for corrosion or mechanical damage
  
• Check adjustment nuts and spring preload settings
  
• Perform a drain test on the travel motor to assess internal leakage
  
• Remove the yoke coupling and inspect splines for wear or stripping
  
• Verify hydraulic pressure at the brake release ports
  

If the brakes hold only on shallow slopes, they may require adjustment or complete rebuild. According to industry standards, aerial lift brakes should hold on grades up to 50% or until tipping occurs.
Repair Considerations and Liability Implications
Repairing the drive system and brakes on a Trailblazer 40 can be challenging due to part availability. Terex used multiple suppliers for hubs and motors, and some components are no longer supported. Seal kits may need to be matched manually at hydraulic shops, and actuator rebuilds require precision.
If selling the machine, full disclosure of the rollaway incident and brake condition is essential. Aerial lifts carry high liability, especially when transporting personnel. Any failure in the drive or brake system could result in serious injury or legal consequences.
One technician recalled servicing a JLG 80HX that had rolled downhill with a worker in the basket. The psychological impact on the operator was severe, and the repair involved complete disassembly of the drive motors, planetary hubs, and brake assemblies.
Engine Identification and Oddball Configurations
The Trailblazer in question featured an Isuzu diesel engine, which was not listed in the original manual. This suggests a factory variation or a later retrofit. Isuzu engines are known for reliability and fuel efficiency, but sourcing parts may require cross-referencing with similar Terex or Genie models.
Operators should document engine serial numbers and compare mounting patterns to confirm compatibility. In some cases, Terex used Isuzu engines for export models or special fleet orders.
Conclusion
A manlift rolling downhill unattended is a serious mechanical and safety failure. In the case of the Trailblazer 40, the incident likely stemmed from compromised brake assemblies and a degraded hydraulic system. While the machine may still function on level ground, its inability to hold position on a slope demands immediate attention.
Repairing the brakes and verifying motor integrity are essential before returning the lift to service or transferring ownership. With aging aerial equipment, mechanical vigilance is not just a matter of performance—it’s a matter of responsibility.