Restoring Front Axle Brakes on the Kenworth W900A

[MikePhua]

The Kenworth W900A and Its Mechanical Heritage
The Kenworth W900A is a classic long-hood conventional truck that helped define heavy-duty hauling in North America during the 1970s and 1980s. Built by Kenworth, a division of PACCAR founded in 1923, the W900A was known for its modular construction, robust frame rails, and customizable drivetrain options. With tens of thousands sold across the U.S. and Canada, it became a favorite among owner-operators and fleet haulers alike.
The W900A’s front axle braking system was typically equipped with drum brakes, actuated by air-over-mechanical linkage. These systems were simple, durable, and field-serviceable, but they require careful setup and maintenance to ensure proper stopping power—especially when paired with heavy loads and steep grades.
Understanding the Front Axle Brake Configuration
Most W900A trucks used a steer axle rated between 12,000 and 14,600 pounds, fitted with S-cam drum brakes. The brake assembly includes:

• Brake shoes
  
• S-cam shaft and bushings
  
• Return springs
  
• Slack adjusters
  
• Brake chambers
  
• Anchor pins and rollers
  

Terminology annotation:

• S-Cam Brake: A rotating shaft with an S-shaped cam that pushes brake shoes outward against the drum.
  
• Slack Adjuster: A lever that converts linear pushrod motion into rotational cam movement, also used to adjust brake clearance.
  
• Brake Chamber: A pneumatic actuator that converts air pressure into mechanical force to apply the brakes.
  

In some configurations, the front axle brakes were deactivated or removed entirely, especially on trucks used in off-road or logging applications. This was done to reduce steering effort or prevent brake lockup on loose terrain. However, for highway use, functional front brakes are essential for balanced stopping and compliance with federal safety regulations.
Challenges in Reinstating Front Brakes
Restoring front axle brakes on a W900A that has had them disabled or removed involves several steps:

• Verifying that the axle is drilled and tapped for brake components
  
• Sourcing compatible brake spiders and backing plates
  
• Installing new brake chambers and plumbing air lines
  
• Matching slack adjusters to camshaft length and angle
  
• Ensuring proper drum-to-shoe clearance and cam rotation direction
  

Recommendations:

• Use OEM or DOT-approved aftermarket components
  
• Replace both sides simultaneously to maintain balance
  
• Torque anchor bolts to spec and use thread-locking compound
  
• Test air pressure delivery and chamber stroke before road use
  

In one restoration project in Montana, a W900A used for oilfield hauling was retrofitted with Bendix brake hardware after decades of operating without front brakes. The technician had to fabricate custom brackets to mount the chambers due to frame modifications made in the 1980s.
Brake Balance and System Integration
Adding or restoring front brakes requires careful attention to brake balance. The W900A’s brake system is split between front and rear axles, with a proportioning valve or quick-release valve managing air delivery. If the front brakes engage too aggressively, they can cause steering instability or premature wear.
Solutions:

• Install a pressure-limiting valve to reduce front brake force
  
• Use matched brake linings with consistent friction ratings
  
• Test brake timing with a stopwatch and air gauge
  
• Adjust slack to achieve equal shoe-to-drum contact across axles
  

In Ontario, a fleet manager retrofitted five W900As with front brakes and noticed a 20% improvement in stopping distance during loaded runs. However, he had to recalibrate the rear brake timing to prevent nose-diving under hard stops.
Legal and Safety Considerations
Federal Motor Carrier Safety Regulations (FMCSR) require that all axles on highway trucks be equipped with functional brakes unless exempted for specific vocational use. Operating without front brakes on public roads can result in fines, insurance denial, or liability in the event of an accident.
Best practices:

• Document all brake modifications and component specs
  
• Perform annual brake inspections and record chamber stroke measurements
  
• Train drivers to recognize brake imbalance and report issues
  
• Use certified mechanics for brake system installation and testing
  

In 2015, a trucking company in Idaho was cited after a DOT inspection revealed disabled front brakes on three W900As. The company had to retrofit the brakes and undergo compliance audits, costing over $30,000 in fines and repairs.
Conclusion
Restoring front axle brakes on a Kenworth W900A is a worthwhile investment in safety, legality, and performance. While some older trucks were configured without them for niche applications, modern road conditions and regulatory standards demand full braking capability. With proper parts, installation, and calibration, the W900A can regain its full stopping power—preserving its legacy while meeting today’s expectations. Whether hauling timber or crossing the Rockies, balanced brakes are the foundation of control.