Hendrickson PRIMAAX EX

Quick Facts

Manufacturer: Hendrickson
Product Name: PRIMAAX EX
Suspension Type: Severe-duty vocational rear air suspension
Axle Configurations: Single, tandem, and tridem
Published Capacities: 23,000 to 78,000 pounds
Ride Heights: Approximately 8.5 to 15.5 inches, depending on configuration
Vertical Axle Travel: Up to 8 inches
Diagonal Wheel Articulation: Up to approximately 12.5 inches
Alignment System: Hendrickson QUIK-ALIGN
Lift-Axle Compatibility: Approved when correctly specified
Engine Torque Restrictions: None published for the listed configurations
Common Applications: Dump, concrete mixer, logging, crane, platform, fire and rescue, heavy-haul, and other vocational vehicles

Overview

The Hendrickson PRIMAAX EX is a severe-duty rear air suspension designed for vocational trucks, heavy-haul tractors, and specialized commercial vehicles. It combines air-ride comfort with the structural strength, stability, and axle articulation required for demanding on-road and job-site operations.

PRIMAAX EX uses large-volume air springs, structural beams, a rigid cross-brace arrangement, heavy-duty frame hangers, shock absorbers, torque rods, and the Hendrickson QUIK-ALIGN axle-alignment system.

The suspension is available in single-, tandem-, and tridem-drive axle configurations. Published capacities range from 23,000 pounds for a single axle to 78,000 pounds for a tridem arrangement.

Key Characteristics

Severe-duty vocational rear air suspension
Available for single, tandem, and tridem drive axles
Published suspension capacities from 23,000 to 78,000 pounds
Large-volume air springs support the vehicle using relatively low air pressure
Up to 8 inches of vertical axle travel
Up to approximately 12.5 inches of diagonal wheel articulation
Optimized suspension geometry provides strong roll stability
Rigid beam-and-cross-brace structure controls suspension movement
Designed to reduce suspension-induced driveline vibration
QUIK-ALIGN system simplifies drive-axle alignment
Premium heavy-duty bushings require no routine lubrication
Approved for properly specified lift-axle applications
Available across several ride heights and axle spacings
No published engine-torque restrictions
Suitable for vocational, severe-duty, and heavy-haul operation

Major Components

Structural Beams: Connect the drive axles to the suspension and transfer vertical, braking, acceleration, and cornering forces.
Square Cross Brace: Connects the structural beams to create a rigid torsion system that supports stability and axle control.
Large-Volume Air Springs: Use compressed air to support the vehicle and help isolate the chassis, body, cargo, and driver from road shock.
Frame Hangers: Attach the suspension to the truck frame and establish the mounting position of the structural beams.
Pivot Bushings: Permit controlled suspension movement at the frame-hanger connections without requiring routine lubrication.
Shock Absorbers: Control suspension movement and help protect the air springs from excessive extension.
Longitudinal Torque Rods: Help control drive-axle windup during acceleration and braking.
Transverse Torque Rods: Restrict lateral axle movement and help keep the axles centered beneath the frame.
QUIK-ALIGN Connections: Allow drive-axle alignment adjustments at the suspension pivot connections.
Height-Control Valve: Adds or exhausts air to maintain the specified ride height as vehicle loading changes.
Air Lines and Fittings: Carry compressed air between the vehicle air supply, height-control valve, and suspension air springs.

How the Suspension System Works

PRIMAAX EX uses compressed air inside flexible air springs to support the rear of the vehicle. When weight is added, the frame moves closer to the axles and activates the height-control valve. The valve supplies additional air until the suspension returns to its specified ride height.

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

The structural beams locate the axles and transfer suspension forces into the frame. Their integrated end caps and square cross brace form a rigid structure that helps control roll and maintain stability.

Shock absorbers damp rapid suspension movement and help prevent the air springs from overextending. Torque rods control axle windup and lateral movement during acceleration, braking, cornering, and travel over uneven surfaces.

The suspension allows the drive axles to move vertically and articulate while maintaining controlled relationships among the axles, frame, air springs, and driveline.

Suspension Position and Function

PPRIMAAX EX is installed beneath the rear portion of a commercial truck or tractor. It connects the frame to a single, tandem, or tridem drive-axle arrangement.

Its primary functions include:

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

Common Specifications

23,000-Pound Configuration: Single axle, approximately 542 pounds installed weight, up to 150,000 pounds GCWR approval, 30,000-pound job-site travel rating, 8 inches of axle travel, approximately 10.75 inches of ground clearance, and available ride heights from approximately 8.5 to 15.5 inches.

26,000-Pound Configuration: Single axle, approximately 651 pounds installed weight, up to 150,000 pounds GCWR approval, 33,000-pound job-site travel rating, 8 inches of axle travel, approximately 10.5 inches of ground clearance, and available ride heights from approximately 8.5 to 15.5 inches.

46,000-Pound Configuration: Tandem axle, approximately 1,078 pounds installed weight, up to 200,000 pounds GCWR approval, 60,000-pound job-site travel rating, 8 inches of axle travel, approximately 10.75 inches of ground clearance, available ride heights from approximately 8.5 to 15.5 inches, and axle spacings from approximately 52 to 72.5 inches.

52,000-Pound Configuration: Tandem axle, approximately 1,292 pounds installed weight, up to 250,000 pounds GCWR approval, 66,000-pound job-site travel rating, 8 inches of axle travel, approximately 10.5 inches of ground clearance, available ride heights from approximately 8.5 to 10.5 inches or 12.5 to 15.5 inches, and axle spacings from approximately 54 to 72.5 inches.

69,000-Pound Configuration: Tridem axle, approximately 1,629 pounds installed weight, up to 300,000 pounds GCWR approval, 90,000-pound job-site travel rating, 8 inches of axle travel, approximately 10.75 inches of ground clearance, available ride heights from approximately 8.5 to 15.5 inches, and axle spacings from approximately 52 to 72.5 inches.

78,000-Pound Configuration: Tridem axle, approximately 1,931 pounds installed weight, up to 400,000 pounds GCWR approval, 99,000-pound job-site travel rating, 8 inches of axle travel, approximately 10.5 inches of ground clearance, available ride heights from approximately 8.5 to 15.5 inches, and axle spacings from approximately 54 to 72.5 inches.

Published installed weights are based on standard configurations using a 10-inch ride height. Other configurations may have different installed weights.

Capacity, Ride Height, and Axle Travel

PRIMAAX EX capacities range from 23,000 pounds for a single drive axle to 78,000 pounds for a tridem-drive axle arrangement.

The suspension must be paired with axles, tires, wheels, brakes, frame components, and driveline equipment rated for the intended load. Installing a higher-capacity suspension does not independently increase the legal or structural capacity of the complete vehicle.

Ride height is measured from the drive-axle centerline to the bottom of the truck frame. The correct ride height affects axle travel, air-spring position, shock-absorber travel, driveline angles, ground clearance, and stability.

PRIMAAX EX provides up to 8 inches of vertical axle travel. The suspension can also provide approximately 12.5 inches of diagonal wheel articulation.

Actual travel may be restricted by the truck manufacturer’s axle stops, shock stroke, frame, body, tires, driveline, or auxiliary equipment.

Ride Quality and Load Distribution

TThe large-volume air springs help isolate the truck frame, body, mounted equipment, cargo, and driver from road impacts. This generally provides a smoother unloaded and loaded ride than a traditional steel-spring or rubber mechanical suspension.

The height-control valve adjusts air pressure as vehicle weight changes. This allows the suspension to maintain a consistent frame-to-axle position across varying load conditions.

In tandem and tridem configurations, the suspension helps distribute weight among the drive axles. Balanced loading depends on correct air pressure, ride height, axle alignment, tire pressure, and vehicle loading.

PRIMAAX EX uses optimized suspension geometry to increase roll stiffness and control body movement. This is particularly important for dump trucks, mixers, cranes, refuse trucks, and other vehicles with high or shifting centers of gravity.

Suspension Controls and Adjustment Options

PRIMAAX EX may use 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
Electronic suspension controls on certain chassis

A driver-operated air-dump control may be included on some vehicles. The suspension may need to be exhausted before certain loading, unloading, towing, stabilizer, or outrigger operations.

Drivers and technicians should follow the procedures supplied by Hendrickson, the truck manufacturer, and the body or equipment manufacturer.

Alignment and Suspension Geometry

Correct alignment helps protect the tires, suspension, driveline, and wheel-end components.

The Hendrickson QUIK-ALIGN system allows technicians to adjust drive-axle alignment at the suspension pivot connection. This helps correct axle thrust angle without using a conventional bar-pin shim arrangement.

Important alignment and geometry measurements 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 position
Frame-hanger location
Axle-bracket location
Air-spring alignment
Shock-absorber travel
Tire and brake clearance

Ride height should be corrected before completing a final axle alignment. An incorrect height can change suspension geometry and driveline angles.

Alignment should also be checked after collision damage, axle replacement, suspension repairs, worn-bushing replacement, abnormal tire wear, or changes in vehicle tracking.

Axle, Brake, and Wheel-End Options

PRIMAAX EX is a suspension system and does not include one universal axle, brake, or wheel-end package. Compatible components are selected by the truck manufacturer for the vehicle’s capacity and application.

Possible configurations include:

Single drive axles
Tandem drive axles
Tridem drive axles
Drum brakes
Air disc brakes
Conventional wheel ends
Preset or unitized wheel ends
Dual rear tires
Approved wide-base single tires
Inter-axle differential locks
Driver-controlled differential locks
Electronic traction control
Tire-pressure monitoring systems

The suspension rating must be matched with appropriate axle, brake, wheel, tire, and driveline ratings. Clearance must be verified throughout the suspension’s complete range of movement.

Common Applications

Vocational trucks
Heavy-haul tractors
Dump trucks
Front-discharge concrete mixers
Rear-discharge concrete mixers
Logging trucks
Crane-mounted trucks
Boom trucks
Platform trucks
Fire and rescue vehicles
Specialty vehicles
Vehicles equipped with outriggers
Medium-duty trucks
Certain bus and recreational-vehicle chassis
Construction and infrastructure vehicles

Vehicle, Axle, and Frame Compatibility

PRIMAAX EX is intended for approved commercial chassis using single-, tandem-, or tridem-drive axles.

Compatibility depends on:

Truck manufacturer and model
Suspension capacity
Drive-axle configuration
Drive-axle ratings
Gross vehicle weight rating
Gross combination weight rating
Frame width and rail dimensions
Ride height
Axle spacing
Wheelbase
Tire and wheel dimensions
Brake configuration
Driveline geometry
Body installation
Lift-axle position
Outrigger installation
Air-system capacity
Available frame and equipment clearance

PRIMAAX EX may be offered as a factory option on selected vocational and heavy-haul trucks. Availability depends on the model, production year, chassis specification, and application approval.

Advantages

Air-ride comfort in vocational service
Available in single-, tandem-, and tridem-axle configurations
Capacities from 23,000 to 78,000 pounds
Up to 8 inches of vertical axle travel
Approximately 12.5 inches of diagonal articulation
Optimized geometry for roll stability
Designed to control suspension-related driveline vibration
Large-volume air springs
QUIK-ALIGN axle-alignment system
Non-lubricated pivot bushings
Approved lift-axle compatibility
Multiple ride heights and axle spacings
No published engine-torque restrictions
Suitable for heavy-haul and severe-duty applications
Helps protect vocational bodies and mounted equipment

Limitations or Considerations

More pneumatic components than a mechanical suspension
Air springs can leak or suffer physical damage
Height-control valves and air lines require inspection
Incorrect ride height can affect driveline geometry
Air-system contamination may interfere with valve operation
Pivot bushings and torque rods remain wear components
High-capacity versions add suspension weight
Vehicle articulation may be restricted by axle stops
Air springs require adequate component clearance
Suspension dump controls must be operated correctly
Alignment and ride-height service require proper procedures
Improper lift-axle operation can overload the drive suspension
Job-site ratings apply only under limited conditions
Not every configuration is available on every chassis

Driver and Operator Experience

PRIMAAX EX generally provides a smoother ride than traditional steel-spring and rubber mechanical suspensions, especially when the vehicle is empty or lightly loaded.

The suspension is designed to retain the roll stability needed for vocational bodies, high payloads, and uneven job-site surfaces. Drivers may experience reduced road shock without the excessive body movement that can occur with an air suspension not designed for severe-duty service.

Drivers should watch for:

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

Changes in normal ride or handling should be inspected before the truck returns to demanding service.

Maintenance and Ownership Notes

PRIMAAX EX uses non-lubricated suspension bushings, but the suspension still requires scheduled inspection.

Maintenance areas include:

Air springs
Height-control valve
Air lines and fittings
Shock absorbers
Structural beams
Square cross brace
Frame hangers
Pivot bushings
QUIK-ALIGN connections
Longitudinal torque rods
Transverse torque rods
Axle brackets
Mounting fasteners
Suspension ride height
Drive-axle alignment
Tire-clearance areas
Brake hoses
ABS wiring

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

Ride height should be measured using the applicable Hendrickson procedure rather than estimated visually.

Fasteners identified as non-reusable by Hendrickson or the truck manufacturer should be replaced instead of 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
Drive-axle misalignment
Lateral axle misalignment
Worn torque-rod bushings
Bent or damaged torque rods
Leaking shock absorbers
Loose mounting fasteners
Damaged structural beams
Damaged cross brace
Cracked frame hangers
Damaged axle brackets
Air-spring misalignment
Restricted axle travel
Incorrect pinion angle
Driveline vibration
Uneven tire wear
Excessive vehicle lean
Harsh or unstable ride
Brake-hose or ABS-wire interference
Insufficient tire or component clearance

Identification Information

PRIMAAX EX can be identified by its large rear air springs, structural beams, square cross brace, frame hangers, torque rods, shock absorbers, and QUIK-ALIGN pivot connections.

Before ordering replacement parts, identify:

Truck manufacturer
Truck model
Production year
Vehicle identification number
Suspension family
Suspension capacity
Single-, tandem-, or tridem-axle configuration
Loaded ride height
Axle spacing
Frame width
Drive-axle manufacturer and model
Brake configuration
Structural-beam design
Air-spring part number
Shock-absorber part number
Height-control valve configuration
QUIK-ALIGN connection
Torque-rod arrangement
Axle-bracket design
Frame-hanger design
Original component numbers

PRIMAAX and PRIMAAX EX components should not be assumed interchangeable. The exact suspension model, capacity, configuration, and component number must be verified.

Buying Considerations

Required suspension capacity
Single-, tandem-, or tridem-axle arrangement
Vehicle gross-weight rating
Gross combination weight
Primary vehicle application
Expected job-site operation
Required ride quality
Roll-stability requirements
Ride height
Axle travel
Ground clearance
Axle spacing
Frame dimensions
Drive-axle compatibility
Brake and wheel-end clearance
Air-system capacity
Lift-axle configuration
Outrigger installation
Body-builder requirements
Installed suspension weight
Payload requirements
Replacement-parts availability
Dealer and service support
Warranty coverage
Total lifecycle cost

The complete specification should be reviewed by the truck manufacturer, Hendrickson, axle supplier, and body builder before ordering.

Variants and Configurations

23,000-Pound Single-Axle Configuration: Designed for single-drive-axle vehicles requiring a heavy-duty rear air suspension.
26,000-Pound Single-Axle Configuration: Provides additional suspension capacity for approved single-drive-axle vocational vehicles.
46,000-Pound Tandem Configuration: Supports common heavy vocational and heavy-haul tandem-drive axle arrangements.
52,000-Pound Tandem Configuration: Provides increased capacity for demanding tandem-drive axle applications.
69,000-Pound Tridem Configuration: Supports three-drive-axle vocational and heavy-haul vehicles.
78,000-Pound Tridem Configuration: Represents the highest-capacity configuration in the published North American PRIMAAX EX range.
Bus, RV, and Medium-Duty Configuration: Hendrickson offers application-specific single-drive-axle versions for certain bus, recreational-vehicle, and medium-duty chassis.

Comparison to Similar Equipment

PRIMAAX EX vs Hendrickson HAULMAAX EX

PRIMAAX EX uses air springs and a height-control system. Hendrickson HAULMAAX EX is a rubber mechanical suspension using bolster and progressive load springs.

PRIMAAX EX generally provides better air-ride comfort and automatic ride-height control. HAULMAAX EX eliminates suspension air springs and may be preferred where mechanical simplicity and loaded stability are higher priorities.

PRIMAAX EX vs Hendrickson PRIMAAX

PRIMAAX EX is an updated severe-duty development of the PRIMAAX suspension design. Hendrickson PRIMAAX remains important for identifying and servicing earlier vehicles.

Components should not be assumed interchangeable between PRIMAAX and PRIMAAX EX.

PRIMAAX EX vs Hendrickson HN

PRIMAAX EX uses air springs to support the vehicle and maintain ride height. Hendrickson HN Vocational Suspension uses a rubber mechanical spring design without suspension air bags.

PRIMAAX EX vs Hendrickson RT/RTE

PRIMAAX EX emphasizes air-ride quality, articulation, and vocational stability. Hendrickson RT/RTE Mechanical Suspension uses a traditional steel-spring walking-beam design.

Best Fit For

Vocational fleets seeking air-ride comfort
Heavy-haul tractors
Dump trucks
Concrete mixers
Logging trucks
Crane and boom vehicles
Fire and rescue vehicles
Platform trucks
Vehicles equipped with outriggers
Single-, tandem-, and tridem-drive axle vehicles
Applications requiring up to a 78,000-pound suspension rating
Trucks requiring increased roll stability
Fleets wanting simplified axle alignment
Vehicles carrying sensitive bodies or equipment
Applications requiring substantial axle articulation

Related Vehicle and Trailer Types

Dump Trucks
Concrete Mixer Trucks
Logging Trucks
Heavy-Haul Trucks
Crane and boom trucks
Platform trucks
Fire and rescue vehicles
Specialty vocational vehicles
Heavy-duty buses
Recreational-vehicle chassis

Related Truck and Trailer Models

Related Suspension Types

Related Equipment Systems

Related Guides

Regulatory and Compliance Notes

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

Liftable pusher and tag axles change the weight carried by the drive suspension. An auxiliary axle should not be raised or unloaded when doing so would overload the PRIMAAX EX suspension, drive axles, frame, tires, or wheels.

Hendrickson’s job-site travel ratings apply only under specific limited conditions. Job-site-rated operation is limited to no more than five percent of vehicle operation and speeds not exceeding five miles per hour.

The suspension must be paired with appropriately rated axles and installed in an application approved by Hendrickson and the vehicle manufacturer.

Real World Operating Notes

PRIMAAX EX is designed for fleets that need air-ride comfort without giving up the stability and durability required in vocational service.

The suspension can help reduce vibration reaching truck bodies, cranes, pumps, tanks, emergency equipment, cargo, and the cab. Its available articulation also helps the drive axles follow uneven job-site surfaces.

Ride quality depends on tire pressure, vehicle loading, body height, frame stiffness, wheelbase, axle spacing, cab suspension, and road conditions.

Frequent operation of the height-control valve may indicate an air leak, incorrect adjustment, unstable loading, or another suspension problem. A vehicle that suddenly sits unevenly or handles differently should be inspected before returning to service.

Frequently Asked Questions

Is Hendrickson PRIMAAX EX an air suspension?

Yes. PRIMAAX EX is a severe-duty rear air suspension that uses large-volume air springs and a height-control system.

What capacities are available?

Published capacities include 23,000 and 26,000 pounds for single axles, 46,000 and 52,000 pounds for tandems, and 69,000 and 78,000 pounds for tridems.

How much axle travel does PRIMAAX EX provide?

Hendrickson publishes up to 8 inches of vertical axle travel and approximately 12.5 inches of diagonal wheel articulation.

What is Hendrickson QUIK-ALIGN?

QUIK-ALIGN is an adjustable suspension connection used to correct drive-axle alignment at the pivot point.

Does PRIMAAX EX require suspension lubrication?

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

Can PRIMAAX EX be used with lift axles?

Yes. Hendrickson lists lift-axle compatibility for the published configurations. The vehicle must remain within all suspension, axle, tire, wheel, and legal weight limits.

Does PRIMAAX EX have engine-torque restrictions?

Hendrickson lists no engine-torque restrictions for the published configurations. All other drivetrain and chassis limits still apply.

How is PRIMAAX EX different from HAULMAAX EX?

PRIMAAX EX is an air suspension. HAULMAAX EX is a rubber mechanical suspension that does not use air springs to support the vehicle.

Can PRIMAAX and PRIMAAX EX parts be interchanged?

Parts should not be assumed interchangeable. The exact suspension model, capacity, configuration, and component number must be identified.

What happens when the ride height is incorrect?

Incorrect ride height can affect axle travel, air-spring position, shock travel, driveline angles, roll stability, and component clearance.

Availability and Where to Find

PRIMAAX EX is available as a factory-installed option on selected vocational trucks, heavy-haul tractors, buses, recreational-vehicle chassis, and specialty vehicles.

Availability depends on the vehicle manufacturer, model, production year, axle configuration, suspension capacity, ride height, axle spacing, frame dimensions, and application approval.

Replacement parts are available through Hendrickson-authorized dealers, commercial truck dealerships, heavy-duty parts suppliers, suspension specialists, and qualified repair facilities.

Before ordering parts, identify the suspension capacity, axle arrangement, ride height, axle spacing, truck model, and original component numbers.

Support Trucking Families

Truck Equipment Atlas supports the mission of Grey Cross, a nonprofit dedicated to helping families of truck drivers who lose their lives while on the road. As the site grows, part of its mission is to bring awareness and support to these families.

Podcast or Video Section

Learn More Through Audio and Video

Truck Equipment Atlas will continue expanding with podcast episodes, interviews, and equipment breakdowns to help drivers and fleets better understand trucks and equipment.

Follow the Growth of Truck Equipment Atlas

Truck Equipment Atlas continues to expand with new truck profiles, trailer coverage, diesel engine pages, equipment system resources, manufacturer information, and educational guides.

Visit our Site Updates page to explore recent additions, project milestones, and upcoming resources as we continue building one of the industry’s growing commercial trucking equipment reference libraries.

View the Latest Site Updates: Truck Equipment Atlas Site Updates