PACCAR DX-40 Tandem Drive Axle

Quick Facts

Manufacturer: PACCAR Inc.
Product Name: PACCAR DX-40
Axle Type: Tandem rear drive axle
Primary Drivetrain Configuration: 6×4
Gross Axle Weight Rating: 40,000 pounds
Published Gross Combination Weight Rating: Up to 80,000 pounds for standard linehaul applications
Published Ratio Range: 2.47 to 3.70
Straight-Torque Compatibility: Up to approximately 1,650 lb-ft
Multitorque Compatibility: Up to approximately 1,750 lb-ft
Primary Applications: Class 8 linehaul and regional-haul tractors
Common Truck Brands: Kenworth and Peterbilt
Key Design Feature: Thru-shaft pinion design
Carrier Construction: Laser-welded carrier design
Published Weight Reduction: Up to approximately 150 pounds compared with heavier traditional configurations
Product Page Slug: paccar-dx-40-tandem-drive-axle

Overview

The PACCAR DX-40 is a 40,000-pound tandem drive axle developed primarily for Class 8 linehaul and regional-haul Kenworth and Peterbilt trucks. It is designed to reduce weight, improve drivetrain efficiency, and provide reliable power transfer in conventional 6×4 tractor configurations.

A thru-shaft pinion design transfers torque through the forward axle and into the interaxle driveline. PACCAR uses advanced manufacturing techniques, including laser-welded carrier construction, to reduce the axle’s weight and eliminate certain internal fasteners.

The DX-40 can be integrated with a PACCAR MX engine and PACCAR automated transmission as part of a complete PACCAR Powertrain specification. PACCAR states that combining these components can provide total powertrain weight savings of up to approximately 500 pounds, depending on the truck configuration.

Key Characteristics

The DX-40 uses a thru-shaft pinion arrangement designed to transfer engine power efficiently through the tandem axle system. This design differs from traditional arrangements that route power through additional internal components before reaching the interaxle driveline.

Spiral-bevel gearing helps optimize the interaxle driveline angle between the forward and rear axles. Proper driveline geometry can reduce vibration and improve universal-joint durability.

High-efficiency pinion and differential bearings are intended to reduce internal power losses. The laser-welded carrier eliminates certain internal fasteners while helping reduce component weight.

A driver-controlled differential lock for the forward axle may be included, depending on the truck specification.

How the Axle or Differential Works

Engine torque travels through the transmission and main driveshaft to the input of the forward tandem axle. The thru-shaft pinion arrangement transfers torque into the forward axle’s gearing and through the interaxle drivetrain.

The interaxle differential divides torque between the forward and rear drive axles while allowing them to rotate at slightly different speeds. This is necessary during turns, suspension movement, and normal differences in tire circumference.

Each axle contains a wheel differential that distributes torque between its left and right wheels. These differentials allow the wheels on opposite sides of the truck to rotate at different speeds while cornering.

When additional traction is needed, the driver can engage approved differential-lock functions. These locks reduce differential action and help distribute torque to additional wheel positions.

Axle Position and Function

The PACCAR DX-40 is installed as the tandem rear drive axle group on compatible Kenworth and Peterbilt trucks. In a standard 6×4 configuration, both rear axles receive engine torque.

The tandem supports the rear portion of the tractor, carries cargo-related fifth-wheel loading, provides final gear reduction, and transfers propulsion and braking forces between the tires and chassis.

The front axle within the tandem is commonly called the forward drive axle. The second unit is called the rear-rear axle. An interaxle driveshaft connects the two.

Common Specifications

Axle Configuration: Tandem rear drive axle
Drivetrain Layout: 6×4
Tandem GAWR: 40,000 pounds
Published Standard GCW Rating: Up to 80,000 pounds
Published Ratio Range: 2.47 to 3.70
Straight-Torque Rating: Up to approximately 1,650 lb-ft
Multitorque Rating: Up to approximately 1,750 lb-ft
Carrier Design: Advanced laser-welded construction
Pinion Design: Thru-shaft pinion
Interaxle Gearing: Spiral-bevel design
Differential Lock: Driver-controlled forward axle differential lock on applicable configurations
Published Axle Weight Reduction: Up to approximately 150 pounds
Potential Complete Powertrain Weight Reduction: Up to approximately 500 pounds when combined with selected PACCAR engine and transmission components
Primary Vehicle Class: Class 8
Primary Truck Brands: Kenworth and Peterbilt

Actual specifications, ratios, torque approvals, brakes, hubs, track widths, suspension compatibility, and warranty coverage depend on the truck’s model year and original build configuration.

Axle Ratios and Gearing

The PACCAR DX-40 has been published with axle ratios ranging from 2.47 to 3.70. The correct ratio depends on engine torque, transmission gearing, tire size, vehicle weight, terrain, cruising speed, and intended application.

Faster numerical ratios such as 2.47 or 2.64 can reduce engine speed at highway cruise. These ratios may support improved fuel efficiency when paired with the correct PACCAR engine and automated transmission.

Higher numerical ratios provide greater torque multiplication. They may be more appropriate for heavier loads, frequent starts, grades, or regional operations with lower average speeds.

The lowest numerical ratio is not automatically the best choice. An axle ratio that is too fast for the application can cause weak launch performance, excessive clutch work, frequent shifting, and difficulty maintaining speed on grades.

Differential and Traction Options

The DX-40 contains an interaxle differential and separate wheel differentials within the forward and rear axle assemblies.

The interaxle differential allows the two axles to compensate for small differences in rotational speed. A driver-controlled interaxle lock can improve torque distribution between the axles during low-traction operation.

A driver-controlled differential lock for the forward axle has been offered on the DX-40. Exact wheel-differential-lock availability should be confirmed using the truck’s build information.

Differential locks should be used according to Kenworth, Peterbilt, and PACCAR operating instructions. Engaging a full lock on dry pavement or during tight turns can cause tire scrub and driveline binding.

Brake and Wheel-End Options

The DX-40 can be configured with approved air drum or air disc brake systems, depending on the Kenworth or Peterbilt truck specification.

Wheel-end options may include conventional hubs, aluminum hubs, and extended-maintenance bearing systems. Exact availability depends on the model year, truck, suspension, wheels, and brake package.

Wide-base or dual-tire configurations may be used when approved for the axle, hubs, wheels, tires, suspension, and vehicle application.

All brake and wheel-end components must support the axle’s 40,000-pound tandem rating and the vehicle’s certified gross axle weight ratings.

Common Applications

Long-haul tractors
Regional-haul tractors
Sleeper trucks
Day cab tractors
Dry van freight operations
Refrigerated freight operations
General freight fleets
Less-than-truckload operations
Dedicated contract carriage
High-mileage highway fleets
Distribution operations
Fuel-efficiency-focused fleets
Class 8 tractors operating near standard legal weights

Truck, Suspension, and Drivetrain Compatibility

The PACCAR DX-40 is designed primarily for compatible Kenworth and Peterbilt Class 8 trucks. Availability depends on truck model, production year, suspension, engine, transmission, and vocation.

The axle may be paired with PACCAR Air Leaf, Low Air Leaf, Flex Air, and other application-approved tandem suspensions. Axle spacing, ride height, torque rods, interaxle driveline angles, and suspension mounts must match the truck specification.

The DX-40 can be paired with a PACCAR MX-13 engine and PACCAR automated transmission as part of an integrated PACCAR Powertrain. Other approved engine and transmission combinations may also be available.

Driveshafts, universal joints, yokes, and transmission output components must be rated for the engine torque and selected axle ratio.

Advantages

40,000-pound tandem capacity
Designed for Class 8 linehaul operation
Up to approximately 150 pounds of axle weight reduction
Potential complete PACCAR Powertrain weight savings of up to 500 pounds
Thru-shaft pinion design
Efficient torque transfer
Laser-welded carrier construction
Reduced use of internal carrier fasteners
High-efficiency pinion and differential bearings
Optimized interaxle driveline angles
Ratios for highway fuel-efficiency applications
Driver-controlled differential-lock availability
Integration with PACCAR engines and transmissions
Kenworth and Peterbilt dealer support
Potential payload and fuel-efficiency benefits

Limitations or Considerations

Primarily intended for highway and regional applications
Not designed to replace heavier vocational tandem axles
Standard published tandem rating is 40,000 pounds
Published standard gross combination weight rating is approximately 80,000 pounds
Ratio range is narrower than some vocational axle families
Availability is concentrated within Kenworth and Peterbilt trucks
Differential-lock configurations vary by truck specification
Specialized PACCAR parts or service information may be required
Tire circumference must remain closely matched across the tandem
Improper differential-lock use can cause driveline damage
Fast ratios require correct engine and transmission matching
Axle capacity does not override tire, wheel, suspension, brake, or frame ratings
Used assemblies must have matching forward and rear axle ratios

Driver and Operator Experience

A correctly specified DX-40 should provide smooth power delivery and low drivetrain noise during highway operation. The optimized interaxle driveline geometry can help reduce vibration through the chassis and cab.

The axle’s lighter design may contribute to increased payload capacity or reduced vehicle weight. Drivers may not feel the weight savings directly, but fleets can benefit through loading flexibility and fuel consumption.

Fast axle ratios used with an automated transmission can produce lower cruising engine speeds. Drivers may notice different shift patterns and greater reliance on the engine’s low-speed torque.

Differential-lock controls should be used only when conditions require additional traction and according to the truck manufacturer’s instructions.

Maintenance and Ownership Notes

Routine maintenance includes checking lubricant levels, inspecting axle breathers, examining pinion and carrier seals, checking wheel ends, and inspecting the interaxle driveshaft.

The correct PACCAR-approved axle lubricant and service interval should be used. Lubricant requirements can vary according to model year, duty cycle, and warranty coverage.

Tire circumference should remain closely matched across the tandem. Mixing tires with substantially different tread depths, sizes, inflation pressures, or constructions can cause continuous interaxle differential activity and premature wear.

Technicians should investigate whining, humming, clunking, vibration, abnormal heat, or visible lubricant leakage before significant damage develops.

Common Axle or Differential Problems

Pinion seal leakage
Carrier or housing lubricant leaks
Wheel-end seal leakage
Restricted axle breathers
Low or contaminated lubricant
Ring-and-pinion gear wear
Pinion-bearing wear
Differential-bearing wear
Interaxle differential damage
Power-divider wear
Differential-lock engagement problems
Axle-shaft damage
Excessive gear backlash
Whining or humming at highway speed
Clunking during acceleration or deceleration
Interaxle driveshaft vibration
Universal-joint or yoke wear
Tire scrub caused by mismatched tire circumference
Wheel-bearing wear or overheating
Brake contamination caused by leaking wheel seals

Identification Information

Manufacturer: PACCAR Inc.
Product Model: DX-40
Product Type: 40,000-pound tandem drive axle
Primary Identification Sources: Axle tags, stamped assembly numbers, and vehicle build records
Forward Axle Information: Model, serial number, assembly number, ratio, and differential-lock configuration
Rear Axle Information: Model, serial number, assembly number, ratio, and differential configuration
Vehicle Information: Kenworth or Peterbilt VIN and original build sheet
Important Drivetrain Information: Ratio, input yoke, interaxle driveline, torque rating, and engine-transmission combination
Important Chassis Information: Suspension, axle spacing, track width, brakes, hubs, wheels, and tires

Both axle assemblies must be identified before ordering gears, bearings, seals, differential components, axle shafts, carriers, or complete replacement axles.

Buying Considerations

Confirmed PACCAR DX-40 identification
Truck make, model, year, and VIN
Forward and rear axle assembly numbers
40,000-pound tandem rating
Original axle ratio
Engine torque rating
Transmission model and gearing
Straight-torque or multitorque configuration
Gross combination weight
Tire size and cruise speed
Suspension model
Axle spacing
Track width
Air drum or air disc brakes
Hub and wheel-end configuration
Interaxle differential-lock arrangement
Forward axle differential-lock availability
Input and interaxle yoke dimensions
Condition of gears, bearings, seals, shafts, and housings
Evidence of overheating, impact damage, overloading, or lubricant contamination
Parts and service availability

Variants and Configurations

Kenworth factory installations
Peterbilt factory installations
Different ratios from 2.47 to 3.70
Straight-torque configurations
Multitorque configurations
Standard wheel differentials
Driver-controlled interaxle differential lock
Forward axle differential-lock configurations
Air drum brake configurations
Air disc brake configurations
Dual-tire configurations
Approved wide-base tire configurations
Steel hub configurations
Aluminum hub configurations
Different PACCAR suspension arrangements
Complete PACCAR Powertrain installations

Comparison to Similar Equipment

The PACCAR DX-40 competes with other 40,000-pound tandem drive axles developed for Class 8 highway tractors.

The Dana Spicer AdvanTEK 40 Tandem Axle offers a broad range of downsped ratios and is available across multiple commercial truck manufacturers.

The Dana Spicer AdvanTEK 40 Pro Tandem Axle provides additional drivetrain-efficiency and powertrain-integration features.

The Detroit Tandem Rear Axle offers multiple highway and vocational ratings and integrates with Detroit engines and DT12 transmissions.

The Meritor 14X HE Tandem Drive Axle is another highway-focused axle designed to support efficient and downsped powertrains.

The DX-40’s main advantage is its integration with Kenworth and Peterbilt trucks and the broader PACCAR Powertrain.

Best Fit For

Kenworth and Peterbilt truck buyers
Fleets wanting a complete PACCAR Powertrain
Class 8 linehaul tractors
Regional-haul tractors
High-mileage highway operations
Fleets operating near standard legal weights
Applications requiring a 40,000-pound tandem rating
Fuel-efficiency-focused fleets
Operators seeking lower drivetrain weight
Trucks using PACCAR MX engines
Trucks using PACCAR automated transmissions
Fleets with access to PACCAR dealer service

Related Truck Types

Sleeper Trucks
Day Cab Trucks
Linehaul Trucks
Regional-Haul Trucks
Class 8 Trucks
Heavy-Duty Trucks

Related Truck Models

Related Axle and Differential Types

Related Equipment Systems

Related Guides

Regulatory and Compliance Notes

The DX-40’s 40,000-pound tandem rating does not independently determine the truck’s legal carrying capacity. Suspension, brakes, hubs, wheels, tires, frame, fifth wheel, and vehicle certification must support the intended load.

Federal, state, provincial, bridge, road, and permit regulations may limit the tandem load below the axle’s mechanical rating.

Both axle assemblies must use matching approved gear ratios. Operating mismatched ratios can create severe drivetrain binding and component damage.

Differential locks must be operated according to PACCAR, Kenworth, or Peterbilt instructions. Improper use can affect vehicle handling and damage gears, axle shafts, tires, or the interaxle driveline.

Real World Operating Notes

The DX-40 is most appropriate for highway tractors operating within its 40,000-pound tandem and approved gross combination weight limits. Fleets regularly operating above standard legal weights may require a heavier axle family.

The axle’s lighter construction can create additional payload capacity, but actual savings depend on the complete truck specification. Engine, transmission, suspension, brakes, wheels, tires, fuel tanks, and accessories all affect final vehicle weight.

Fast ratios can reduce engine rpm and fuel consumption when correctly matched to the powertrain. They may provide poor results if the truck regularly starts heavy loads on steep grades or operates primarily at low speeds.

Frequently Asked Questions

What is the PACCAR DX-40?

The DX-40 is a 40,000-pound tandem drive axle developed for Kenworth and Peterbilt Class 8 trucks, particularly linehaul and regional-haul tractors.

What is a thru-shaft pinion?

A thru-shaft pinion transfers power through the forward axle toward the rear axle while also driving the forward axle gearing. PACCAR uses this design to improve power transfer and axle efficiency.

What axle ratios are available?

The published ratio range is approximately 2.47 to 3.70. Exact availability depends on truck model, engine, transmission, and model year.

How much weight can the DX-40 carry?

The tandem axle group has a published gross axle weight rating of 40,000 pounds. Legal loading may be lower because of vehicle components or applicable regulations.

What engine torque can it handle?

Published information identifies compatibility up to approximately 1,650 lb-ft in straight-torque applications and 1,750 lb-ft in approved multitorque applications.

How much lighter is the DX-40?

PACCAR states that the axle can be up to approximately 150 pounds lighter. A complete PACCAR Powertrain configuration may provide total weight savings of up to approximately 500 pounds.

Does the DX-40 have differential locks?

A driver-controlled differential lock for the forward axle has been offered. Interaxle and wheel-differential-lock availability should be confirmed through the truck’s build records.

Is the DX-40 suitable for heavy haul?

It is primarily a 40,000-pound linehaul axle. Heavy-haul operations exceeding its axle, torque, or gross combination weight approvals generally require a heavier axle configuration.

Which trucks offer the DX-40?

The DX-40 is available on compatible Kenworth and Peterbilt trucks. Exact availability changes according to model and production year.

Can it be paired with a PACCAR MX-13?

Yes. The DX-40 can be integrated with the PACCAR MX-13 and a PACCAR automated transmission as part of a complete PACCAR Powertrain.

Why must tandem tires be matched?

Differences in tire circumference force the interaxle differential to compensate continuously. Excessive mismatch can cause heat, tire scrub, and premature driveline wear.

Can one DX-40 axle be replaced without replacing the other?

Potentially, but the replacement must match the original ratio, capacity, housing, differential configuration, suspension, brakes, wheel ends, and interaxle drivetrain.

Availability and Where to Find

The PACCAR DX-40 is available as original equipment on compatible Kenworth and Peterbilt trucks. Availability depends on the truck model, model year, engine, transmission, suspension, and application.

Replacement components and complete assemblies may be obtained through authorized Kenworth and Peterbilt dealers, PACCAR Parts locations, axle rebuilders, and qualified heavy-truck parts suppliers.

Used assemblies should be verified using both axle identification tags and the truck’s original build records. The forward and rear axle ratios must match.

Current product information is available from the PACCAR DX-40 product page.

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