Hendrickson Primaax Suspension Parts List: Complete Guide

The Hendrickson Primaax suspension is a lightweight, integrated air-ride system used on heavy-duty trailers. It combines the axle beam, air springs, and shock absorbers into a single, maintenance-friendly unit. Knowing the parts list is essential for ordering replacements, performing repairs, or simply understanding how the system works. This guide covers every major component you’re likely to encounter, with practical notes on selection and installation.

Major Components of the Hendrickson Primaax Suspension

The Primaax system is modular. Each axle position uses a set of parts that work together to provide ride comfort and durability. Here’s a breakdown of the key groups.

Axle Beam Assembly

The axle beam is the central structural member that connects the wheel ends to the suspension hangers. On the Primaax, the beam is a forged, lightweight design that also serves as the lower mount for the air springs and shocks. The beam itself is typically not serviced separately; if damaged, the entire axle-beam assembly may need replacement. However, individual components like the beam end bushings are replaceable.

• Axle Beam – Part numbers vary by axle capacity and track width. Common capacities: 22,500 lb, 25,000 lb.
• Beam End Bushings – Pressed into the beam ends to interface with the hanger brackets. Typical part: Primaax beam bushing kit (e.g., 64770-003).

Hanger Brackets

Hanger brackets attach the suspension to the trailer frame. They provide the pivot point for the axle beam. The Primaax uses a cast steel hanger with a removable bushing cartridge.

• Hanger Bracket Assembly – Left and right, specific to frame width and axle spacing. Part numbers often start with 64770.
• Hanger Bushing and Pin Kit – Includes the elastomeric bushing and the hardened pin that goes through the beam end. Example kit: 64770-012.

Air Springs

Air springs (air bags) support the load and provide ride height adjustment. The Primaax uses a rolling lobe air spring mounted between the axle beam and the frame bracket. Each axle position uses two air springs (one per side).

• Air Spring – Standard part: Firestone or Goodyear rolling lobe. Example part: W01-358-9200 (Firestone). Always check the height and load rating.
• Air Spring Piston – The lower part of the air spring that attaches to the beam. Some kits include the piston; others require it separately.
• Air Spring Mounting Hardware – Bolts, washers, and spacer plates (part numbers vary).

Shock Absorbers

The Primaax uses a single shock absorber per side, mounted between the axle beam and the frame. Shocks control oscillation and improve ride quality.

• Shock Absorber – Heavy-duty gas-charged. Part numbers: Monroe 72100 series or Hendrickson specific (e.g., 64770-027). Length and valving vary by application.
• Shock Bushing Kit – Upper and lower bushings for the shock mounts.

Torque Rods (Control Arms)

Torque rods locate the axle fore and aft and control braking torque. The Primaax typically uses a single torque rod on each side, connecting the axle beam to the frame.

• Torque Rod Assembly – Solid or tubular, with bonded rubber bushings at each end. Example: 64770-045 (length depends on wheelbase).
• Torque Rod Bushings – Replaceable; available as a kit. Common kit: 64770-046.

Height Control Valve and Linkage

The height control valve maintains the correct ride height regardless of load. It connects to the axle beam via a linkage rod.

• Height Control Valve – Typically a Haldex or Wabco unit. Example: 64770-060.
• Height Control Valve Linkage – Rod and clevis assembly. Part numbers vary by length.
• Dual Height Control Valve – Some configurations use two valves for better leveling.

Bump Stops and Spring Pads

Bump stops prevent metal-to-metal contact in a full-compression event. Spring pads distribute load.

• Bump Stop – Rubber or urethane, mounted on the frame above the axle beam. Part: 64770-070.
• Axle Beam Spring Pad – Located between the air spring piston and the beam. Example: 64770-075.

Fasteners and Hardware Kits

Many suspension bolts are torque-to-yield and should not be reused. Hardware kits include all necessary fasteners for a specific repair.

• Air Spring Mounting Bolts – Grade 8 bolts with lock nuts. Example kit: 64770-080.
• Hanger Bolt Kit – Includes bolts for attaching hanger to frame. Torque specific.
• Shock Mount Bolts – Typically ½-inch grade 8.

How to Identify the Correct Parts

The Primaax suspension has been produced in several generations (e.g., Primaax EX, Primaax L). Part numbers can differ. Always verify:

• Axle capacity (stamped on beam or axle tag)
• Axle track (standard or wide)
• Ride height (usually 6–8 inches)
• Year of manufacture

Cross-reference your trailer VIN or suspension serial number with Hendrickson’s online catalog for the most accurate list.

Common Replacement Scenarios

Air Spring Replacement

Air springs are the most frequently replaced component. If the suspension sags or fails to lift, inspect the air spring for cracks or leaks. Replace both sides at the same time. Use genuine Hendrickson or equivalent brand.

Bushing Wear

Worn hanger bushings cause loose steering and clunking. Replace the bushing and pin kit (64770-012). Note that the beam end bushings require a press for removal and installation.

Height Control Valve Malfunction

If the suspension does not maintain ride height or continuously exhausts air, the valve or linkage may be faulty. Check the linkage for binding and the valve for internal damage.

Practical Buying and Installation Guidance

• Always buy from a heavy-duty truck parts dealer. Avoid used parts for critical safety components.
• Compare prices on genuine Hendrickson vs. aftermarket. Aftermarket bushings and shocks can be acceptable, but air springs and torque rods are best from OEM to ensure fit and durability.
• If replacing the entire suspension, consider the Primaax EX upgrade kit for improved payload.
• Installation requires proper tools: torque wrenches, press for bushings, and jack stands. If you’re not experienced, have a certified shop do the work.

Final Recommendation

Keep a spare parts kit on hand for common failures: a pair of air springs, a hanger bushing kit, and a height control valve. Always consult the Hendrickson Primaax parts manual for your specific model year and axle capacity. Proper maintenance of these components extends trailer life and improves safety. For a full list of part numbers, download the Primaax parts catalog from Hendrickson’s website.