Hendrickson PRIMAAX

Quick Facts

Manufacturer: Hendrickson
Product Name: PRIMAAX
Suspension Type: Heavy-duty vocational rear air suspension
Product Status: Earlier-generation suspension largely succeeded by PRIMAAX EX
Axle Configurations: Single, tandem, and tridem configurations were produced
Common Capacities: Approximately 23,000 to 78,000 pounds, depending on the original configuration
Primary Suspension Medium: Large-volume air springs
Alignment System: Hendrickson QUIK-ALIGN
Common Applications: Vocational trucks, heavy-haul tractors, dump trucks, concrete mixers, logging trucks, cranes, refuse trucks, and specialty vehicles
Brake Compatibility: Drum and application-specific air disc brake configurations
Replacement Parts: Available according to the original vehicle, suspension, axle, and production configuration
Important Identification Note: PRIMAAX and PRIMAAX EX are different suspension generations, and parts should not be assumed interchangeable

Overview

The Hendrickson PRIMAAX is an earlier-generation heavy-duty rear air suspension developed for vocational, severe-service, and heavy-haul commercial vehicles. It was designed to combine air-ride comfort with the axle control, stability, durability, and articulation required for demanding truck applications.

PRIMAAX uses air springs, structural support beams, a cross-tube assembly, pivot connections, torque rods, shock absorbers, frame hangers, and the Hendrickson QUIK-ALIGN axle-alignment system.

The suspension was produced in several vehicle-specific configurations for single-, tandem-, and tridem-drive axles. Exact specifications vary considerably because PRIMAAX systems were engineered around individual truck manufacturers, chassis models, axle capacities, ride heights, axle spacings, and brake packages.

PRIMAAX was followed by the updated Hendrickson PRIMAAX EX, which introduced revised components and suspension geometry. The original PRIMAAX remains important because many trucks equipped with it are still operating and require correct identification, maintenance, and replacement parts.

Key Characteristics

Heavy-duty vocational rear air suspension
Earlier generation of the PRIMAAX suspension family
Available in single-, tandem-, and tridem arrangements
Designed for vocational and heavy-haul vehicles
Large-volume air springs
Structural support beams and cross-tube assembly
QUIK-ALIGN axle-alignment system
Longitudinal and transverse torque rods
Heavy-duty shock absorbers
Non-lubricated rubber suspension bushings
Designed to control axle windup and frame rise
Multiple capacities, ride heights, and axle spacings
Truck-manufacturer-specific configurations
Drum and application-specific air disc brake compatibility
Requires accurate model identification before ordering parts

Major Components

Support Beams: Connect the drive axles to the suspension pivot points and transfer vehicle loads into the frame.
Cross Tube: Joins the support beams and contributes to the suspension’s roll control and structural stability.
Air Springs: Support the vehicle and payload with compressed air while helping isolate the frame and body from road impacts.
Frame Hangers: Attach the suspension pivot connections to the vehicle’s frame rails.
QUIK-ALIGN Pivot Connections: Connect the support beams to the frame hangers and provide the adjustment used for drive-axle alignment.
Pivot Bushings: Permit controlled suspension movement without requiring routine lubrication.
D-Pin Connections: Form part of the beam-to-axle connection used on applicable PRIMAAX configurations.
Top Pads and Bottom Caps: Secure and position the suspension and axle components within the clamp group.
U-Bolts and Clamp Hardware: Attach the axle to the support-beam assembly on applicable configurations.
Longitudinal Torque Rods: Control axle windup and help maintain the proper pinion-angle relationship.
Transverse Torque Rods: Restrict side-to-side axle movement beneath the chassis.
Shock Absorbers: Control suspension movement and protect the air springs from excessive extension.
Height-Control Valve: Adds or releases air to maintain the specified suspension ride height.
Air Lines and Fittings: Carry compressed air between the vehicle air supply, height-control valve, and air springs.

How the Suspension System Works

PRIMAAX uses compressed air within flexible air springs to support the rear of the truck. When the vehicle is loaded, the suspension compresses and activates the height-control valve. The valve supplies additional air until the frame returns to the specified ride height.

When weight is removed, the height-control valve exhausts excess air and lowers the frame to its designed position.

The support beams locate the axles and transfer vertical, braking, acceleration, and cornering forces through the suspension. The cross tube connects the beams and helps the system resist roll and twisting movement.

Longitudinal torque rods help control axle windup during acceleration and braking. Transverse torque rods restrict lateral axle movement and help maintain the correct axle position beneath the chassis.

Shock absorbers damp repeated suspension movement and help prevent the air springs from overextending.

The suspension’s geometry allows the axles to move over uneven surfaces while helping maintain proper driveline angles and vehicle stability.

Suspension Position and Function

PRIMAAX is installed beneath the rear section of the vehicle frame and connects the chassis to its drive axle or drive-axle group.

Its primary functions include:

Supporting the rear chassis and payload
Maintaining the specified ride height
Connecting the drive axles to the frame
Absorbing road and job-site impacts
Allowing controlled axle travel
Helping maintain drive-tire contact
Controlling axle windup
Restricting lateral axle movement
Improving ride quality
Helping protect the body and mounted equipment
Providing roll control for vocational applications

Common Specifications

PRIMAAX was produced in multiple OEM-specific versions, so exact specifications must be confirmed using the truck manufacturer’s build information and Hendrickson service literature.

Common original configurations included:

Single-drive axle arrangements in approximately 23,000- and 26,000-pound classes
Tandem-drive axle arrangements in approximately 40,000-, 46,000-, and 52,000-pound classes
Tridem-drive axle arrangements reaching approximately 69,000 to 78,000 pounds in certain applications
Multiple loaded ride heights
Multiple tandem and tridem axle spacings
Drum-brake configurations
Application-specific air disc brake configurations
Vocational and heavy-haul approvals
Hendrickson QUIK-ALIGN axle adjustment
Large-volume air springs
Heavy-duty shock absorbers

Available specifications changed according to truck manufacturer, model, production year, frame width, brake system, and intended application.

Capacity, Ride Height, and Axle Travel

PRIMAAX capacity depends on the exact suspension and axle configuration installed by the vehicle manufacturer. The suspension identification and vehicle build information should be checked before using any published capacity figure.

The suspension must be paired with appropriately rated:

Drive axles
Truck frame
Tires and wheels
Brakes
Wheel ends
Driveline components
Body and mounted equipment

Ride height is measured from the drive-axle centerline to the bottom of the truck frame. The correct measurement varies by the original vehicle and suspension configuration.

An incorrect ride height can affect:

Air-spring position
Available axle travel
Shock-absorber movement
Driveshaft operating angles
Axle pinion angles
Ground clearance
Vehicle roll stability
Tire and component clearance

The truck manufacturer’s axle stops, body installation, driveline, tires, and auxiliary equipment may limit the suspension’s available travel.

Ride Quality and Load Distribution

PRIMAAX was designed to provide improved ride quality compared with traditional vocational steel-spring suspensions while maintaining the stability required for heavy truck applications.

The air springs adjust to changes in vehicle loading. The height-control valve increases or decreases suspension air pressure to maintain the designed frame-to-axle relationship.

In tandem and tridem configurations, the suspension helps distribute load across the drive axles. Correct load distribution depends on proper ride height, air pressure, axle alignment, tire inflation, and vehicle loading.

The suspension’s structural arrangement also helps control axle windup and frame rise during acceleration and braking. This can reduce suspension-related driveline vibration and improve vehicle handling.

Suspension Controls and Adjustment Options

PRIMAAX may include several pneumatic and mechanical controls.

Height-control valve
Suspension air-dump valve when specified
Air-pressure protection components
Air-supply lines and fittings
QUIK-ALIGN axle adjustment
Transverse torque-rod shims
Available ride-height settings
Application-specific axle stops
Application-specific shock absorbers
Single or dual height-control valve arrangements
Driver-operated dump controls on certain vehicles

The availability and operation of these controls depend on the truck manufacturer and original vehicle specification.

A suspension dump control should only be used according to the instructions provided by the vehicle, body, and suspension manufacturers.

Alignment and Suspension Geometry

The QUIK-ALIGN system allows technicians to adjust axle alignment at the suspension pivot connection. The system uses an eccentric alignment collar to reposition the axle and correct thrust angle.

Important alignment and geometry considerations include:

Drive-axle thrust angle
Axle-to-axle alignment
Lateral axle position
Suspension ride height
Axle pinion angle
Driveshaft operating angle
Pivot-bushing position
Torque-rod length and position
Frame-hanger location
Axle-bracket position
Air-spring alignment
Shock-absorber travel
Tire and brake clearance

Ride height should be checked before final axle alignment because an incorrect height can change suspension and driveline geometry.

PRIMAAX systems were produced with different pivot fastener sizes and component configurations. The existing hardware should be physically identified before replacement parts or torque specifications are selected.

Axle, Brake, and Wheel-End Options

PRIMAAX is a suspension system and does not include one universal axle, brake, or wheel-end package.

Depending on the original truck specification, it may be paired with:

Single drive axles
Tandem drive axles
Tridem drive axles
Drum brakes
Application-specific air disc brakes
Conventional wheel ends
Preset wheel ends
Unitized wheel ends
Dual rear tires
Approved wide-base single tires
Inter-axle differential locks
Driver-controlled differential locks
Electronic traction-control systems

PRIMAAX applications using air disc brakes may require different longitudinal torque rods or other components to provide adequate brake clearance.

Axle, brake, wheel-end, tire, and suspension capacities must be compatible with the complete vehicle rating.

Common Applications

Vocational trucks
Heavy-haul tractors
Dump trucks
Concrete mixer trucks
Refuse trucks
Logging trucks
Crane-mounted trucks
Boom trucks
Platform trucks
Fire and rescue vehicles
Construction vehicles
Specialty trucks
Vehicles equipped with outriggers
Certain medium-duty vehicles
Certain bus and motorhome chassis

Vehicle, Axle, and Frame Compatibility

PRIMAAX was installed on selected commercial chassis from several truck manufacturers. Compatibility depends on the exact factory-designed configuration.

Important compatibility factors include:

Truck manufacturer
Truck model
Production year
Vehicle identification number
Suspension capacity
Single-, tandem-, or tridem-axle arrangement
Drive-axle manufacturer and model
Frame width
Frame-rail dimensions
Ride height
Axle spacing
Wheelbase
Brake configuration
Tire and wheel dimensions
Driveline geometry
Body installation
Lift-axle position
Outrigger installation
Air-system capacity
Available component clearance

A used PRIMAAX suspension should not be transferred to another chassis without engineering approval from the appropriate manufacturers.

Advantages

Air-ride comfort for vocational trucks
Designed for heavy-duty and severe-service applications
Single-, tandem-, and tridem configurations
Multiple capacity ranges
Automatic ride-height control
Controlled axle movement
Strong roll stability
Reduced suspension-related driveline vibration
QUIK-ALIGN axle adjustment
Non-lubricated pivot bushings
Large-volume air springs
Multiple axle-spacing options
Vocational and heavy-haul compatibility
Replacement support remains available for many existing systems

Limitations or Considerations

An earlier-generation suspension rather than Hendrickson’s current PRIMAAX EX design
Exact specifications vary by truck manufacturer and configuration
Air springs, valves, fittings, and lines can leak
Incorrect ride height can affect driveline geometry
Pivot bushings and torque rods are wear components
QUIK-ALIGN hardware must remain correctly tightened
Different pivot fastener sizes were used
Brake configurations may require different components
PRIMAAX and PRIMAAX EX parts may not be interchangeable
Legacy parts may require additional identification work
Not every component remains available as an individual replacement
Complete beam or service kits may replace earlier individual components
Air springs can be damaged by abrasion, heat, debris, or incorrect alignment
Improper dump-valve use can damage the suspension

Driver and Operator Experience

PRIMAAX generally provides a smoother ride than traditional mechanical vocational suspensions, especially when the truck is empty or lightly loaded.

The air springs help reduce road shock reaching the cab, body, cargo, and mounted equipment. The suspension’s structural geometry helps maintain stability when the truck is loaded.

Drivers should watch for:

Vehicle leaning
Incorrect rear ride height
Continuous height-control valve activity
Audible air leaks
Harsh or bouncy ride
Increased body roll
Driveline vibration
Vehicle pulling or dog-tracking
Uneven drive-tire wear
Suspension clunks or knocks
Air springs rubbing nearby components
Slow suspension recovery after loading

A noticeable change in ride height, handling, or vibration should be inspected before the truck returns to severe-duty operation.

Maintenance and Ownership Notes

PRIMAAX requires regular inspection even though its pivot bushings do not require routine lubrication.

Important maintenance areas include:

Air springs
Height-control valve
Air lines and fittings
Shock absorbers
Support beams
Cross tube
Frame hangers
Pivot bushings
QUIK-ALIGN connections
D-pin connections
U-bolts and clamp hardware
Longitudinal torque rods
Transverse torque rods
Axle brackets
Mounting fasteners
Suspension ride height
Drive-axle alignment
Brake-hose clearance
ABS wiring
Tire-wear patterns

Technicians should inspect for air leaks, rubber deterioration, loose fasteners, damaged brackets, worn bushings, shock-absorber leakage, and evidence of component movement.

PRIMAAX service procedures and parts often differ according to the original truck manufacturer. The correct vehicle-specific Hendrickson technical publication should be used.

Fasteners identified as non-reusable should be replaced rather than reinstalled.

Common Suspension Problems

Air-spring leaks
Cracked or abraded air springs
Incorrect ride height
Damaged height-control valve
Leaking air lines or fittings
Worn pivot bushings
Loose QUIK-ALIGN hardware
Worn D-pin bushings
Loose U-bolts or clamp hardware
Drive-axle misalignment
Lateral axle misalignment
Worn torque-rod bushings
Bent or damaged torque rods
Leaking shock absorbers
Damaged support beams
Cracked or damaged cross tube
Damaged frame hangers
Damaged axle brackets
Air-spring misalignment
Restricted axle travel
Incorrect pinion angle
Driveline vibration
Uneven tire wear
Vehicle lean
Brake-hose or ABS-wire interference
Insufficient tire or component clearance

Identification Information

PRIMAAX can be identified by its large rear air springs, support-beam and cross-tube assembly, frame hangers, torque rods, shock absorbers, D-pin axle connections, and QUIK-ALIGN pivot hardware.

Before ordering replacement parts, record:

Truck manufacturer
Truck model
Production year
Vehicle identification number
Suspension name
Suspension capacity
Axle configuration
Ride height
Axle spacing
Frame width
Drive-axle manufacturer
Drive-axle model
Brake type
Support-beam part number
Cross-tube part number
Air-spring part number
Shock-absorber part number
Torque-rod configuration
Frame-hanger design
Axle-connection design
QUIK-ALIGN fastener size
Original casting and assembly numbers

The PRIMAAX name is sometimes used informally when referring to PRIMAAX EX. The installed system must be physically identified before parts are ordered.

Buying Considerations

Original suspension identification
Truck manufacturer and model
Production year and VIN
Suspension capacity
Single-, tandem-, or tridem arrangement
Ride height
Axle spacing
Frame width
Drive-axle compatibility
Brake configuration
Pivot fastener size
Support-beam and cross-tube design
Air-spring part numbers
Replacement-parts availability
Complete service-kit availability
Previous repairs or modifications
Vehicle alignment
Suspension air leaks
Condition of bushings and torque rods
Condition of frame and axle brackets
Dealer and technical support
Repair cost compared with vehicle value

When buying a used truck, the suspension should be inspected for mismatched components, previous welding, nonstandard fasteners, incorrect ride height, and air-spring interference.

Variants and Configurations

Single-Axle PRIMAAX: Produced for selected medium- and heavy-duty chassis requiring a vocational rear air suspension.
Tandem-Axle PRIMAAX: Used on many heavy vocational trucks and tractors, with several capacity, ride-height, and axle-spacing combinations.
Tridem-Axle PRIMAAX: Used on specialized heavy-haul and severe-duty vehicles requiring three rear drive axles.
Drum-Brake Configuration: Uses suspension and torque-rod components designed around drum-brake clearance.
Air Disc Brake Configuration: Certain applications use alternate torque rods, brackets, or other components to provide adequate air disc brake clearance.
Truck-Manufacturer-Specific Configuration: PRIMAAX systems were produced for specific chassis from Mack, Volvo, Kenworth, International, Freightliner, Western Star, and other manufacturers.

Comparison to Similar Equipment

PRIMAAX vs Hendrickson PRIMAAX EX

PRIMAAX is the earlier suspension generation. Hendrickson PRIMAAX EX uses revised structural components, axle connections, geometry, and application options.

Both are heavy-duty rear air suspensions, but replacement components should not be selected by appearance alone.

PRIMAAX vs Hendrickson HAULMAAX EX

PRIMAAX uses air springs and automatic ride-height control. Hendrickson HAULMAAX EX uses rubber bolster and progressive load springs without suspension air bags.

PRIMAAX generally provides a softer air-ride response. HAULMAAX EX eliminates several pneumatic suspension components.

PRIMAAX vs Hendrickson HAS

PRIMAAX was designed for severe-duty vocational and heavy-haul applications. Hendrickson HAS Air Suspension is a lighter vocational rear air-suspension family commonly used in 40,000- and 46,000-pound tandem applications.

PRIMAAX vs Hendrickson RT/RTE

PRIMAAX uses air springs and height-control valves. Hendrickson RT/RTE Mechanical Suspension uses steel springs and walking beams for traditional severe-duty mechanical operation.

Best Fit For

Owners maintaining trucks originally equipped with PRIMAAX
Vocational fleets requiring air-ride comfort
Heavy-haul tractors
Dump trucks
Concrete mixers
Logging trucks
Refuse trucks
Crane and boom vehicles
Platform trucks
Specialty vocational equipment
Single-, tandem-, and tridem-drive axle vehicles
Fleets needing correct legacy suspension identification
Buyers evaluating used vocational trucks

Related Vehicle and Trailer Types

Dump Trucks
Concrete Mixer Trucks
Refuse Trucks
Logging Trucks
Heavy-Haul Trucks
Crane and boom trucks
Platform trucks
Fire and rescue vehicles
Specialty vocational trucks

Related Truck and Trailer Models

Related Suspension Types

Related Equipment Systems

Related Guides

Regulatory and Compliance Notes

The suspension’s original capacity does not independently determine the truck’s legal operating weight. The vehicle must remain within all applicable axle, tire, wheel, brake, gross vehicle weight, gross combination weight, and bridge-formula limits.

Repairs should preserve the truck manufacturer’s original suspension geometry, ride height, axle spacing, brake clearance, and driveline relationships.

Substituting PRIMAAX EX or unrelated components into an original PRIMAAX installation without approval may change the suspension’s performance and structural integrity.

Vehicles with liftable auxiliary axles must not be operated in a way that overloads the PRIMAAX drive suspension or other chassis components.

Real World Operating Notes

Many PRIMAAX-equipped trucks have been in service for years, making previous repairs and component substitutions important inspection considerations.

A truck may contain updated replacement assemblies while retaining other original PRIMAAX components. Parts should be identified individually instead of assuming the complete suspension remains in its original configuration.

Air leaks, incorrect ride height, worn pivot bushings, loose clamp hardware, and axle misalignment can produce similar handling or tire-wear symptoms.

When inspecting a used vehicle, compare components on both sides and across all drive axles. Mismatched air springs, beams, shocks, torque rods, or pivot hardware may indicate an incomplete or incorrect repair.

Frequently Asked Questions

Is Hendrickson PRIMAAX still a current suspension?

The original PRIMAAX is an earlier-generation system that has largely been succeeded by PRIMAAX EX. Replacement parts and service support remain relevant for trucks still equipped with PRIMAAX.

Is PRIMAAX an air suspension?

Yes. PRIMAAX is a rear air suspension that uses air springs and a height-control system to support the vehicle.

Is PRIMAAX the same as PRIMAAX EX?

No. PRIMAAX and PRIMAAX EX are different generations. They share some design concepts, but their components should not be assumed interchangeable.

What capacities were available?

PRIMAAX was produced in multiple configurations ranging from single-axle vocational applications to high-capacity tandem and tridem systems. The exact rating must be confirmed from the original vehicle and suspension information.

What is QUIK-ALIGN?

QUIK-ALIGN is Hendrickson’s adjustable pivot connection used to correct drive-axle alignment.

Does PRIMAAX require suspension lubrication?

Its rubber pivot bushings do not require routine lubrication. Other chassis, axle, brake, driveline, and wheel-end components may still require lubrication.

How is the ride height measured?

Ride height is generally measured from the drive-axle centerline to the bottom of the truck frame. The correct specification depends on the vehicle configuration.

Can PRIMAAX use air disc brakes?

Certain PRIMAAX configurations were designed for air disc brakes. These systems may use different torque rods, brackets, or suspension components for clearance.

Can PRIMAAX EX parts be installed on PRIMAAX?

Some service kits may update or replace earlier components, but interchangeability must be confirmed through the correct Hendrickson parts and service literature.

How can I identify PRIMAAX correctly?

Record the truck VIN, suspension capacity, ride height, axle spacing, beam numbers, air-spring numbers, pivot hardware, and axle configuration before ordering parts.

Availability and Where to Find

Original PRIMAAX suspensions are generally found on existing vocational trucks, heavy-haul tractors, specialty vehicles, and used chassis rather than being selected for new production.

Replacement parts may be available through Hendrickson-authorized dealers, commercial truck dealerships, heavy-duty suspension suppliers, salvage-equipment suppliers, and qualified repair facilities.

Some original components may have been superseded by updated service assemblies or replacement kits. The truck VIN, suspension model, axle arrangement, ride height, and original component numbers should be provided when locating parts.

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