Meritor 14X Tandem Drive Axle

Quick Facts

Manufacturer: Meritor, now part of Cummins
Official model family: MT-14X
Equipment type: Tandem rear-drive axle
Drive configuration: 6×4 tandem drive
Available ratings: 34,000, 40,000, and 44,000 pounds
Available axle ratios: 2.28:1 through 7.17:1, depending on model
Ring-gear diameter: 15.31 inches
Inter-axle differential: Standard tandem power-divider configuration
Maximum inter-axle differential torque capacity: Up to 2,050 pound-feet
Differential lock: Optional driver-controlled differential lock
Primary applications: Highway, construction, utility, fire and rescue, heavy haul, and vocational trucks
Related high-efficiency version: Meritor 14X HE

Overview

The Meritor 14X Tandem Drive Axle, officially identified in the current Cummins product catalog as the MT-14X Tandem Rear Drive Axle, is a widely used tandem-drive system for heavy commercial trucks.

The family includes configurations rated at 34,000, 40,000, and 44,000 pounds. Its available gearing extends from fuel-efficiency-focused highway ratios to deeper ratios for vocational and heavy-haul applications.

The forward-rear axle receives torque from the transmission through the main driveshaft. Its inter-axle differential divides torque between the forward-rear and rear-rear drive axles. Each axle contains a wheel differential that distributes torque between its left and right wheels.

Cummins lists the MT-14X for truck, construction and utility, fire and rescue, and heavy-haul applications. The family offers 22 published axle ratios ranging from 2.28:1 through 7.17:1, although the exact range depends on the selected axle rating and configuration.

Key Characteristics

Single-reduction tandem-drive architecture
34,000-, 40,000-, and 44,000-pound tandem ratings
Twenty-two available axle ratios across the complete family
Large inter-axle differential
Inter-axle torque capacity up to 2,050 pound-feet
High-torque gear design
Premium Amboid gearing on applicable configurations
Rugged single-piece differential carrier
Optional driver-controlled differential lock
Optional forward-and-reverse lubrication pump
Standard-track, DualTrac, and wide-track housing options
Compatibility with dual and wide-base-single tires
Highway, vocational, and heavy-haul configurations
Related 14X HE high-efficiency version

How the Axle or Differential Works

Power from the engine passes through the transmission and main driveshaft to the input yoke on the forward-rear 14X axle.

Inside the forward carrier, the power divider and inter-axle differential direct torque along two paths. Part of the torque passes through the forward-rear wheel differential and axle shafts to the first set of drive wheels.

The remaining torque travels through the output shaft and short inter-axle driveshaft to the rear-rear axle. Its pinion turns the ring gear, and the rear wheel differential distributes torque through the axle shafts to the second set of drive wheels.

The inter-axle differential allows small differences in rotational speed between the two drive axles. Each wheel differential allows the left and right wheels on its axle to rotate at different speeds during turns.

Engaging the inter-axle differential lock connects the forward-rear and rear-rear drive axles so torque continues reaching both axles during low-traction operation.

An optional driver-controlled wheel differential lock can provide another level of traction by connecting the left and right axle shafts within the equipped axle.

Axle Position and Function

The Meritor 14X tandem consists of a forward-rear axle and a rear-rear axle.

The forward-rear axle is the first axle in the tandem group. It receives power directly from the transmission and contains the inter-axle differential and power divider that distribute torque between both drive axles.

The rear-rear axle is positioned behind the forward-rear axle. It receives power through the short inter-axle driveshaft and transfers that power through its ring-and-pinion gearset, wheel differential, axle shafts, and wheel ends.

Major forward-rear components include:

• Main input yoke
• Input shaft
• Inter-axle differential
• Power-divider assembly
• Output shaft and yoke
• Ring-and-pinion gearset
• Wheel differential
• Axle shafts
• Wheel ends

Major rear-rear components include:

• Input yoke
• Pinion shaft
• Ring-and-pinion gearset
• Wheel differential
• Axle shafts
• Wheel ends

Common Specifications

• MT-34-14X tandem rating: 34,000 pounds
• MT-34-14X published highway GCW rating: Up to 80,000 pounds
• MT-34-14X standard ratios: 2.28 through 4.11, with optional ratios available
• MT-40-14X tandem rating: 40,000 pounds
• MT-40-14X published highway GCW rating: Up to 145,000 pounds depending on operating grade
• MT-40-14X standard ratios: 2.28 through 7.17
• MT-44-14X tandem rating: 44,000 pounds
• MT-44-14X published GCW rating: Up to 145,000 pounds in applicable paved-road conditions
• MT-44-14X standard ratios: 3.70 through 5.86
• Ring-gear diameter: 15.31 inches
• Axle-shaft spline: 2.10 inches with 41 teeth
• Axle-shaft body diameter: 1.88 or 2.00 inches, depending on configuration
• Housing box size: 5.25 × 4.62 inches
• Wheel-end series: Meritor R-series
• Housing options: Standard track, DualTrac, and wide track
• Differential lock: Optional on applicable configurations
• Lubrication pump: Optional for demanding vocational applications

Published ratings depend on the exact axle model, grade, gearing, vehicle configuration, and manufacturer approval. They do not establish universal legal operating limits.

Axle Ratios and Gearing

The complete MT-14X family offers 22 published axle ratios.

• 2.28
• 2.47
• 2.64
• 2.79
• 2.85
• 3.08
• 3.25
• 3.36
• 3.42
• 3.55
• 3.70
• 3.90
• 4.11
• 4.33
• 4.63
• 4.88
• 5.29
• 5.86
• 6.14
• 6.43
• 6.83
• 7.17

Not every ratio is available with every axle rating.

Lower numerical ratios are generally used in highway trucks configured for lower cruising engine speed and improved fuel efficiency.

Higher numerical ratios provide greater torque multiplication and are commonly selected for vocational, heavy-haul, off-highway, and lower-speed applications.

Axle-ratio selection should consider:

• Engine torque curve
• Transmission gearing
• Direct-drive or overdrive configuration
• Tire revolutions per mile
• Gross combination weight
• Required cruising speed
• Startability
• Gradeability
• Operating terrain
• Highway or vocational duty cycle

Both drive axles in the tandem must use matching ratios. A mismatch can cause continuous inter-axle differential operation, excessive heat, driveline windup, tire wear, and severe component damage.

Differential and Traction Options

The Meritor 14X uses an inter-axle differential to distribute torque between the forward-rear and rear-rear drive axles.

Cummins states that the MT-14X has an inter-axle differential that is 20% larger and supports torque capacity up to 2,050 pound-feet. This design is intended to improve reliability under high-input-torque conditions.

Available traction-related equipment may include:

• Inter-axle differential
• Driver-controlled inter-axle differential lock
• Open wheel differentials
• Optional driver-controlled wheel differential lock
• Antilock braking system integration
• Automatic traction-control integration

The inter-axle lock connects the two drive axles. A wheel differential lock connects the left and right axle shafts within an equipped axle.

The exact lock configuration should be confirmed using the truck’s build sheet, axle identification information, external actuators, and cab controls.

Brake and Wheel-End Options

The MT-14X may be configured with brake and wheel-end equipment selected according to the truck manufacturer, axle rating, suspension, tire arrangement, and duty cycle.

Available or commonly integrated options include:

• Air drum brakes
• Air disc brakes
• Conventional wheel bearings
• Preset wheel bearings
• Oil-lubricated wheel ends
• Meritor R-series wheel ends
• Dual rear tires
• Wide-base-single tires
• Standard-track housings
• DualTrac housings
• Wide-track housings
• ABS wheel-speed sensors
• Automatic traction-control integration
• Tire-pressure monitoring equipment

Common Applications

Long-haul highway tractors
Regional-haul tractors
Heavy-duty day cabs
Construction trucks
Dump trucks
Concrete mixers
Fire and rescue trucks
Heavy wreckers
Utility trucks
Refuse trucks
Logging trucks
Oilfield trucks
Heavy-haul tractors
Severe-service vehicles

Truck, Suspension, and Drivetrain Compatibility

The Meritor 14X is used in heavy commercial trucks with conventional tandem-drive layouts.

Compatibility depends on:

• Truck manufacturer
• Chassis model
• Model year
• Vehicle build specification
• Required axle rating
• Engine torque
• Transmission model
• Driveshaft configuration
• Suspension type
• Suspension ride height
• Frame width
• Brake package
• Wheel-end arrangement
• Tire size
• Track width
• Gross combination weight
• Intended duty cycle

The axle can be paired with mechanical and air-ride tandem suspensions when the housing, mounting brackets, torque rods, driveline angles, and ride height are correctly specified.

The truck’s VIN and original build information should be checked before assuming compatibility.

Advantages

Broad range of axle ratios
Three principal tandem capacity ratings
Suitable for highway and vocational applications
High inter-axle differential torque capacity
Optional driver-controlled differential lock
Optional forward-and-reverse lubrication pump
Rugged single-piece carrier construction
Standard- and wide-track configurations
Compatibility with dual and wide-base tires
Established replacement-parts availability
Extensive service support
Related high-efficiency version available
Multiple gross-combination-weight configurations
Long history in heavy commercial trucks

Limitations or Considerations

Heavier and more complex than a single-drive axle
More gears, bearings, seals, brakes, and wheel ends to maintain
Available ratios vary by axle rating
Both tandem carriers must use matching ratios
Differential locks require proper driver operation
Deep ratios can raise engine rpm during highway operation
Fast ratios require proper engine and transmission matching
Axle rating alone does not establish legal vehicle weight
Replacement carriers must match the exact axle position
Lubricant requirements vary by configuration and duty cycle
Mismatched tire diameters can damage the inter-axle differential
Individual options vary by truck manufacturer

Driver and Operator Experience

The Meritor 14X is designed to provide predictable tandem-drive operation across highway and vocational applications.

Its high-torque gearing and rigid carrier design support smooth and quiet operation. Cummins also identifies reduced vibration and improved ride quality as benefits associated with the Premium Amboid design.

Driver experience depends on:

• Axle ratio
• Transmission gearing
• Tire size
• Vehicle weight
• Suspension type
• Road surface
• Differential-lock configuration
• Engine calibration

A highway truck with a fast axle ratio may operate at relatively low cruising rpm. A vocational truck with deeper gearing generally provides stronger low-speed response and control but may operate at higher rpm on the highway.

Drivers should understand the difference between the inter-axle lock and optional wheel differential locks. Locks should be operated according to the truck and axle manufacturers’ instructions.

Maintenance and Ownership Notes

Important maintenance practices include:

• Check the axle lubricant level.
• Use the approved lubricant specification.
• Follow the required lubricant-change interval.
• Inspect the carrier, pinion, and wheel seals.
• Keep axle breathers clean and open.
• Inspect the input and output yokes.
• Check universal joints and driveshafts.
• Inspect differential-lock air lines and wiring.
• Confirm that differential locks engage and release.
• Monitor axle and wheel-end temperatures.
• Inspect magnetic drain plugs during service.
• Check suspension ride height.
• Inspect torque rods and bushings.
• Maintain proper axle alignment.
• Match tire sizes and tread depths across both drive axles.
• Investigate new noise or vibration promptly.

The optional forward-and-reverse pump is designed to maintain lubrication during demanding vocational operation in either direction.

Lubricant quantities and service procedures should be obtained from the service information for the exact axle and housing configuration.

Common Axle or Differential Problems

Pinion-seal leakage
Wheel-seal leakage
Carrier-joint leakage
Gear howl
Bearing growl
Excessive backlash
Driveline clunking
Power-divider noise
Inter-axle differential overheating
Differential lock failing to engage
Differential lock failing to release
Ring-and-pinion damage
Carrier-bearing wear
Pinion-bearing wear
Metal contamination
Mismatched tandem ratios
Mismatched tire diameters
Worn axle-shaft splines
Housing or suspension-mount damage

Identification Information

Common model designations include:

• MT-34-14X
• MT-40-14X
• MT-44-14X

Identification information may be found on:

• Axle identification tag
• Differential carrier tag
• Axle housing
• Stamped housing surface
• Vehicle build sheet
• Original equipment records
• Manufacturer parts catalog
• Fleet service records

Record the following information:

• Complete axle model
• Serial number
• Assembly number
• Customer number
• Forward-rear or rear-rear position
• Axle ratio
• Differential-lock configuration
• Brake configuration
• Wheel-end configuration
• Housing and track-width option

The forward-rear and rear-rear carriers are not interchangeable merely because they belong to the same axle family. The forward axle contains the inter-axle differential and power-divider equipment.

Before ordering a replacement carrier, verify the model, ratio, axle position, differential type, yokes, lock configuration, and axle-shaft compatibility.

Buying Considerations

• Required tandem rating
• Gross vehicle weight
• Gross combination weight
• Highway or vocational duty cycle
• Engine torque
• Transmission gearing
• Required axle ratio
• Direct-drive or overdrive transmission
• Tire size
• Standard- or wide-track housing
• Dual or wide-base tires
• Suspension compatibility
• Brake configuration
• Differential-lock requirements
• Lubrication-pump requirements
• Startability
• Gradeability
• Highway cruising rpm
• Operating terrain
• Service support
• Replacement-parts availability
• New, used, or remanufactured component availability
A used axle or carrier should be inspected for correct identification, ratio, gear condition, bearing condition, contamination, leaks, and signs of overheating.

Variants and Configurations

• MT-34-14X
• MT-40-14X
• MT-44-14X
• Standard-track housing
• DualTrac housing
• Wide-track housing
• Highway ratios
• Vocational ratios
• Hypoid-geared configurations
• Premium Amboid configurations
• Open wheel differentials
• Driver-controlled differential lock
• Optional forward-and-reverse lubrication pump
• Drum-brake configurations
• Disc-brake configurations
• Dual-tire wheel ends
• Wide-base-single wheel ends
• Meritor 14X HE high-efficiency version
The related 14X HE is a 40,000-pound North American highway-focused tandem. It uses high-efficiency bearings, precision-finished spiral-bevel gearing, laser-welded ring-gear construction, and the Meritor Lube Management System.
Cummins publishes ratios from 2.15 through 3.90 and engine-torque capability up to 1,850 pound-feet for the 14X HE.

Comparison to Similar Equipment

The standard MT-14X offers a wider selection of axle ratings, ratios, and vocational configurations than the highway-focused 14X HE.

The 14X HE concentrates on reducing mechanical losses in 40,000-pound highway applications through:

• High-efficiency bearings
• Precision-finished spiral-bevel gearing
• Laser-welded ring-gear construction
• Meritor Lube Management System
• Reduced lubricant-churning losses
• Highway-focused fast ratios

The heavier Meritor RT-160 and RT-180 families are intended for higher-capacity and more demanding vocational applications.

Compared with a 6×2 system, the 6×4 Meritor 14X tandem powers both rear axles. A 6×2 may reduce vehicle weight and mechanical losses, while the 14X generally provides stronger traction and broader vocational capability.

Best Fit For

Fleets requiring a conventional 6×4 tandem
Long-haul tractors
Regional tractors
Heavy-duty day cabs
Construction trucks
Dump trucks
Concrete mixers
Fire and rescue vehicles
Heavy wreckers
Logging trucks
Oilfield trucks
Heavy-haul applications
Fleets requiring broad axle-ratio availability
Operations requiring optional wheel differential locks
Buyers seeking established parts and service support

Related Truck Types

• Sleeper Trucks
• Long-Haul Sleeper Trucks
• Day Cab Trucks
• Vocational Trucks
• Severe-Service Trucks
• Heavy-Haul Trucks
• Dump Trucks

Related Truck Models

• Freightliner Cascadia
• Freightliner 114SD
• Freightliner 122SD
• Western Star 47X
• Western Star 49X
• Kenworth T680
• Kenworth T880
• Kenworth T800
• Peterbilt 579
• Peterbilt 389
• International LT Series
• International HX Series
• Volvo VNL
• Volvo VNX
• Mack Anthem
• Mack Granite

Related Axle and Differential Types

• Commercial Truck Drive Axles
• Truck Differentials
• Lift Axles and Auxiliary Axles
• Commercial Truck Steer Axles
• Electric Drive Axles
• Commercial Trailer Axles

Related Equipment Systems

• Engines
• Transmissions
• Suspension Systems
• Brake Systems
• Tires and Wheels
• Electrical Systems
• Safety Systems

Regulatory and Compliance Notes

The axle’s mechanical rating does not establish the truck’s legal operating weight.

Legal limits may also depend on:

• Vehicle certification
• Gross vehicle weight rating
• Gross combination weight rating
• Individual axle ratings
• Tire ratings
• Axle spacing
• Bridge formulas
• Federal regulations
• State and provincial laws
• Posted road limits
• Seasonal restrictions
• Permit conditions

Brake, ABS, wheel-end, tire, and suspension components must be matched to the axle rating and vehicle application.

Any axle modification, ratio change, housing replacement, or capacity change should be reviewed against the truck manufacturer’s certification and applicable regulations.

Real World Operating Notes

The MT-14X covers a much wider range of applications than its basic tandem-axle description suggests.

A 40,000-pound highway tandem with a 2.28 ratio will operate very differently from a 44,000-pound vocational tandem with a 5.29 ratio. The housing, gearing, engine speed, startability, grade performance, and duty cycle must be evaluated as one complete specification.

When inspecting a used truck:

• Verify that both carrier ratios match.
• Compare tire sizes and tread depths.
• Test power-divider operation.
• Confirm that differential locks engage and release.
• Check the lubricant for large metal particles.
• Inspect the housing and suspension mounts.
• Look for wheel-seal and pinion-seal leaks.
• Listen for abnormal howl, growl, or clunking.
• Check for axle or wheel-end overheating.
• Verify the axle model against the truck’s build records.

Frequently Asked Questions

Is the Meritor 14X the same as the MT-14X?

The product family is commonly called the Meritor 14X. Cummins currently identifies the standard tandem model as the MT-14X Tandem Rear Drive Axle.

What ratings are available?

The standard family includes 34,000-, 40,000-, and 44,000-pound tandem ratings.

What axle ratios are available?

The complete family offers 22 published ratios from 2.28:1 through 7.17:1. The exact ratios depend on the selected model.

Is the Meritor 14X a single axle?

No. The MT-14X covered on this page is a tandem-drive family with forward-rear and rear-rear axles.

Does the Meritor 14X have locking differentials?

A driver-controlled differential lock is available on applicable configurations. The exact inter-axle and wheel-lock equipment should be confirmed from the truck’s build specification.

Can the Meritor 14X use wide-base-single tires?

Yes. Applicable DualTrac and housing configurations can support wide-base-single or conventional dual-tire arrangements.

Can different ratios be used in the two tandem axles?

No. The forward-rear and rear-rear carriers must have matching ratios.

Is the 14X HE the same as the standard MT-14X?

No. The 14X HE is a related highway-focused, high-efficiency version built on the 14X platform.

Is the Meritor 14X suitable for heavy haul?

Certain MT-14X configurations are listed for heavy-haul applications. The required axle rating, gross-combination rating, ratio, engine torque, terrain, and permit requirements must still be evaluated.

Who currently supports Meritor axle products?

Meritor is part of Cummins. Current product information, parts resources, and support are available through Cummins, authorized dealers, and drivetrain specialists.

Availability and Where to Find

The MT-14X remains part of Cummins’ current commercial axle portfolio.

New axle availability depends on:

• Truck manufacturer
• Chassis model
• Factory option availability
• Axle rating
• Axle ratio
• Brake configuration
• Wheel-end configuration
• Suspension
• Production schedule
• Geographic market

Used and remanufactured components may be available through:

• Cummins and Meritor distributors
• Authorized truck dealers
• Heavy-truck parts suppliers
• Differential and driveline specialists
• Fleet-surplus suppliers
• Commercial-truck salvage operations
• Meritor Parts Xpress

Official product information: Cummins Meritor MT-14X Tandem Rear Drive Axle

Parts resource: Meritor Parts Xpress

Confirm the complete model, serial number, assembly number, axle position, ratio, and differential-lock configuration before purchasing.

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