Dana Spicer S172 Series

Quick Facts

Manufacturer: Dana Incorporated
Brand: Spicer
Product Family: S172 Series
Axle Type: Single-reduction single drive axle
Supported Drive Configurations: 4×2, 6×2, and 8×2
Primary Vehicle Classes: Class 7 and Class 8
Primary Models: S21-172, S23-172, and S25-172
GAWR Range: 21,000 to 25,000 lb
Maximum Published Nominal GCW: Up to 100,000 lb in referenced configurations
Axle Ratio Range: 3.07:1 to 6.14:1
Primary Applications: Linehaul, regional haul, and vocational trucks
Gearing Technology: Low-offset High-Power Density AdvanTEK gearing
Lubrication Design: Passive lubricant-management system
Differential Options: Standard wheel differential and optional driver-controlled differential lock
Notable Configuration: Spicer EconoTrek 6×2 system with a non-driven tag axle
Primary Design Goal: Reduce weight and drivetrain losses while retaining heavy-duty single-axle capacity

Overview

The Dana Spicer S172 Series is a family of heavy-duty single commercial truck drive axles for Class 7 and Class 8 vehicles.

The series includes the S21-172, S23-172, and S25-172, providing gross axle weight ratings from 21,000 to 25,000 pounds. Dana developed the S172 for 4×2, 6×2, and 8×2 chassis layouts.

Unlike a conventional 6×4 tandem, an S172-equipped 6×2 truck uses one powered rear axle and one non-driven support axle. This reduces driveline weight and mechanical losses but provides fewer driven wheel positions.

The S172 retains the strength and durability of Dana’s earlier S170 single-drive platform while reducing axle weight by more than 60 pounds.

Its principal technologies include low-offset AdvanTEK gearing, high-strength pinion bearings, passive lubricant management, heavy-wall housing options, and an available driver-controlled wheel differential lock.

Key Characteristics

The S172 uses wide-face High-Power Density AdvanTEK gearing. The wider gear teeth provide additional contact area for transmitting engine torque without requiring an unnecessarily large or heavy axle assembly.

A low hypoid offset reduces sliding action between the ring-and-pinion gears. This design is intended to improve mechanical efficiency while maintaining strength and reducing noise, vibration, and harshness.

High-strength pinion bearings support the pinion under heavy vehicle loads and high drivetrain torque. Proper bearing support helps maintain gear alignment and can extend ring-and-pinion life.

The passive lubricant-management system uses a Venturi-style differential cover and a patented lubricant meter. These features direct oil toward critical bearings while reducing the amount of lubricant exposed to unnecessary churning.

The S172 can be paired with a Dana tag axle as part of the Spicer EconoTrek 6×2 system. Dana has stated that this configuration can weigh up to 380 pounds less than a typical 6×4 tandem.

How the Axle or Differential Works

Engine torque travels through the transmission and driveshaft to the S172’s input yoke and pinion shaft.

The pinion gear turns the larger ring gear inside the axle carrier. The ratio between these two gears provides the vehicle’s final-drive reduction.

The ring gear is connected to the wheel differential. This differential divides torque between the left and right axle shafts while allowing the two wheels to rotate at different speeds during turns.

When equipped with a driver-controlled wheel differential lock, the axle can temporarily connect the left and right sides more directly. This improves traction when one wheel is on a slippery or low-traction surface.

Because the S172 is a single drive axle, it does not have the power divider or inter-axle differential found in the D172 tandem axle.

In a 6×2 configuration, the S172 provides propulsion while a non-driven tag or pusher axle supports additional vehicle weight.

For a broader explanation of these components, see How Commercial Truck Axles and Differentials Work.

Axle Position and Function

In a 4×2 vehicle, the S172 is the truck’s single rear axle. It supports rear vehicle weight while transmitting engine torque to both rear wheel positions.

In a 6×2 vehicle, the S172 is combined with a non-driven auxiliary axle. Depending on the chassis design, the non-driven axle may be installed ahead of or behind the drive axle.

In an 8×2 configuration, the truck uses additional non-driven axle positions to increase carrying capacity while retaining one powered rear axle.

The S172 supports part of the vehicle’s weight, provides final-drive reduction, distributes torque between the rear wheels, and carries the brakes, hubs, bearings, wheels, tires, and suspension mounts.

Its rated capacity does not automatically establish the truck’s legal axle load. The suspension, tires, wheels, brakes, frame, axle spacing, and vehicle certification must also support the load.

Common Specifications

Axle Design: Single-reduction single drive axle
Vehicle Classes: Class 7 and Class 8
Supported Chassis Layouts: 4×2, 6×2, and 8×2
Primary Models: S21-172, S23-172, and S25-172
S21-172 Maximum GAW: 21,000 lb
S23-172 Maximum GAW: 23,000 lb
S25-172 Maximum GAW: 25,000 lb
Maximum Published Nominal GCW: 100,000 lb in referenced S172 configurations
Published Ratio Range: 3.07:1 to 6.14:1
Available Ratios: 3.07, 3.21, 3.42, 3.58, 3.73, 3.91, 4.10, 4.30, 4.56, 4.78, 5.25, 5.38, 5.57, and 6.14
Nominal Ring-Gear Diameter: Approximately 17.3 inches
Axle-Shaft Body Diameter: Approximately 2.06 inches
Axle-Shaft Splines: 46 splines in referenced configurations
Spline Diameter: Approximately 2.35 inches
Housing Wall Thickness: Model- and application-dependent, including approximately 11 mm and 12.5 mm configurations
Gearing Type: Low-offset wide-face AdvanTEK gearing
Lubrication System: Passive lubricant management with metered flow
Differential Option: Integrated driver-controlled wheel differential lock
Tire Configuration: Dual or approved wide-base single tires
Special Configuration: EconoTrek 6×2 system with a non-driven tag axle

All ratings and equipment remain subject to Dana and OEM application approval.

Axle Ratios and Gearing

The S172 offers axle ratios from 3.07:1 through 6.14:1. This range allows the axle to support highway, regional, and vocational applications.

Ratios such as 3.07, 3.21, and 3.42 are suited to highway-oriented trucks with adequate engine torque and compatible transmission gearing. These ratios can reduce engine rpm during cruising.

Ratios such as 3.58, 3.73, 3.91, 4.10, and 4.30 balance road speed, startability, grade performance, and fuel efficiency.

Ratios such as 4.56, 4.78, 5.25, 5.38, 5.57, and 6.14 provide greater torque multiplication. They may be appropriate for vocational vehicles, frequent starts, steep grades, large tires, heavy loads, or reduced operating speeds.

The S172’s low hypoid offset reduces the sliding motion between the ring and pinion. This can reduce frictional losses compared with designs using a larger hypoid offset.

The axle ratio must be matched to the engine, transmission, tire revolutions per mile, vehicle weight, operating speed, terrain, and expected startability.

Learn more in Commercial Truck Axle Ratios Explained.

Differential and Traction Options

A standard S172 wheel differential allows the left and right wheels to rotate at different speeds during turns.

An integrated driver-controlled wheel differential lock is available for applications requiring additional traction and spinout protection.

When engaged, the lock restricts differential action so both drive wheels can contribute more directly to moving the truck.

A differential lock is especially useful on snow, mud, gravel, wet grass, loading areas, and uneven surfaces. However, a single locked drive axle still does not provide the same traction as two powered axles in a 6×4 drivetrain.

Drivers should engage the lock before excessive wheelspin develops and follow the truck manufacturer’s operating-speed limitations.

The lock should not remain engaged during tight turns on firm, dry pavement. Doing so can cause tire scrub, driveline windup, difficult steering, and axle damage.

See Open vs Locking vs Limited-Slip Differentials for more information.

Brake and Wheel-End Options

S172 installations may use heavy-duty drum brakes or commercial air-disc brakes. Exact availability depends on the truck manufacturer and axle specification.

Brake packages can include different drums, rotors, calipers, chambers, slack adjusters, dust shields, ABS sensors, and parking-brake components.

Wheel-end configurations may use conventional serviceable bearings or extended-maintenance hub systems. Hub, bearing, spindle, and seal specifications vary by model.

The axle can support dual tires or approved wide-base single tires. Dana’s SelecTTrac option helps match axle, wheel-end, and bearing requirements to the selected tire arrangement.

A 6×2 chassis may include load-transfer or traction-management controls that shift some weight from the non-driven axle toward the S172 during low-traction conditions.

Brake and wheel-end parts must be ordered using the complete axle identification and OEM build information.

Common Applications

Class 7 straight trucks
Class 8 highway tractors
Single-drive-axle tractors
Linehaul trucks using a 6×2 configuration
Regional-haul trucks
Pickup-and-delivery trucks
Weight-sensitive freight operations
Fuel-conscious fleet applications
Municipal trucks
Utility vehicles
Approved vocational trucks
Vehicles using a 4×2 drivetrain
Vehicles using an EconoTrek 6×2 system
Vehicles using an 8×2 configuration
Applications requiring a 21,000- to 25,000-pound drive axle

Truck, Suspension, and Drivetrain Compatibility

The S172 is designed for Class 7 and Class 8 trucks using 4×2, 6×2, or 8×2 configurations.

In a 4×2 truck, the S172 operates as the only rear axle. In 6×2 and 8×2 trucks, additional non-driven axles support weight without receiving engine torque.

The axle must be matched to the engine, transmission, driveshaft, tires, wheels, suspension, frame, brake system, and expected operating weight.

The S172 can be paired with a Dana tag axle in the EconoTrek 6×2 system. This arrangement is designed to reduce weight, rolling resistance, and maintenance compared with a traditional 6×4 tandem.

A 6×2 tractor may require electronic traction management, load transfer, or a liftable non-driven axle to maintain acceptable drive-axle loading.

Vehicles operating in deep snow, mud, soft job sites, steep off-road terrain, or other low-traction environments may be better suited to a 6×4 tandem.

Advantages

Supports 4×2, 6×2, and 8×2 chassis configurations
Available in 21,000-, 23,000-, and 25,000-pound ratings
More than 60 pounds lighter than the preceding S170 design
Broad ratio coverage supports highway and vocational work
Low hypoid offset reduces internal friction
Wide-face AdvanTEK gearing provides high strength
High-Power Density design controls size and weight
High-strength pinion bearings support heavy loads
Passive lubricant management reduces churning losses
Lower lubricant volume can reduce axle weight
Available FE and XFE lubricants may further improve efficiency
Driver-controlled differential lock improves traction
Heavy-wall housing options support demanding applications
SelecTTrac supports dual and wide-base single tires
EconoTrek 6×2 configuration can reduce vehicle weight
A 6×2 arrangement eliminates the power divider and inter-axle driveshaft
Fewer powered axle components can reduce maintenance
Reduced mechanical losses can improve fuel efficiency

Limitations or Considerations

A single drive axle provides less traction than a 6×4 tandem
The complete drive-axle load is concentrated on one powered axle
A 6×2 truck requires careful weight distribution
The non-driven axle may need load-transfer or lift controls
Traction can decrease when too much weight rests on the non-driven axle
The S172’s 25,000-pound maximum rating does not override legal axle-weight limits
A 100,000-pound nominal GCW requires application approval
Not every ratio is available for every model or truck
Low numerical ratios can reduce startability under heavy loads
High numerical ratios increase highway engine speed
Severe vocational work may require a tandem drive axle
Driver-controlled differential locks add controls and service requirements
Wide-base single tires require compatible wheel ends and axle ratings
EconoTrek weight and efficiency benefits vary by truck specification and duty cycle
S170 and S172 components should not be assumed to interchange

Driver and Operator Experience

A properly specified S172 can provide a smooth and efficient driving experience in highway and regional operations.

The low-offset gearing is designed to reduce axle noise and mechanical losses. Drivers may notice less gear whine during cruising or coast operation.

A 6×2 truck can feel different from a conventional 6×4 because only one rear axle provides propulsion. Wheel slip may occur sooner when the drive axle is lightly loaded.

Load-transfer systems can temporarily increase weight on the powered axle during starts or low-traction conditions. Drivers should understand how the truck’s system operates and any speed limitations that apply.

The wheel differential lock can improve traction when one side of the drive axle begins to slip. It should be engaged according to the vehicle manufacturer’s instructions.

Drivers should report unusual vibration, axle noise, lubricant odor, warning lights, traction problems, or difficulty engaging or releasing the differential lock.

Maintenance and Ownership Notes

The S172 should be maintained according to Dana service literature and the vehicle manufacturer’s maintenance schedule.

Correct lubricant type and fill level are essential because the axle uses a managed lubricant-flow system. Overfilling can increase churning losses, while underfilling can damage gears and bearings.

Dana FE and XFE lubricants may be approved for selected applications. Lubricant choice should follow the axle specification, duty cycle, climate, service interval, and warranty requirements.

Routine inspections should include the pinion seal, differential cover, wheel seals, breather, housing, suspension brackets, hubs, brakes, and differential-lock components.

Driveshaft universal joints, yokes, slip joints, and fasteners should be inspected for wear, looseness, and lubrication requirements.

In a 6×2 configuration, the non-driven axle, load-transfer system, lift mechanism, air controls, and suspension settings also require maintenance.

Tire diameter should remain closely matched across rear axle positions. Large differences in tire size can affect load distribution, braking, and stability.

Common Axle or Differential Problems

Pinion-seal leakage
Differential-cover leakage
Wheel-seal leakage
Clogged or damaged axle breather
Low or contaminated lubricant
Restricted passive lubricant flow
Ring-and-pinion gear whine
Carrier-bearing noise
Pinion-bearing wear
Excessive gear backlash
Wheel differential damage caused by spinout
Differential lock that will not engage
Differential lock that will not release
Pneumatic or electrical problems affecting the lock
Axle-shaft or spline wear
Wheel-bearing looseness or overheating
Driveline vibration from worn universal joints
Housing damage caused by overloading or impact
Uneven tire wear in 6×2 or 8×2 configurations
Insufficient drive-axle loading in slippery conditions
Load-transfer or tag-axle control problems

See Common Truck Axle and Differential Problems for additional diagnostic guidance.

Identification Information

Manufacturer: Dana Incorporated
Product Family: Spicer S172 Series
Primary Models: S21-172, S23-172, and S25-172
Axle Type: Single-reduction single drive axle
Identification Sources: Axle tag, carrier tag, housing stampings, and OEM build records
Important Information to Record: Complete model number, serial number, specification number, ratio, and truck VIN

The axle-identification tag is normally attached to the housing or carrier area. Its exact location may vary by installation.

The S21, S23, and S25 portions of the model designations correspond to the family’s general 21,000-, 23,000-, and 25,000-pound capacity levels.

Complete suffix information may identify housing thickness, differential-lock equipment, brakes, wheel ends, gearing, and other features.

If the identification tag is missing, use the vehicle VIN, OEM build sheet, housing stampings, carrier numbers, ring-gear markings, hub information, brake identification, and physical measurements.

Use How to Identify a Truck Axle or Differential before ordering parts.

Buying Considerations

Confirm whether the axle is an S21-172, S23-172, or S25-172
Record the complete model and suffix information
Verify the serial and specification numbers
Confirm the gross axle weight rating
Check the truck’s certified axle and gross weight ratings
Verify the nominal GCW approval
Confirm the axle ratio
Match the ratio to the engine, transmission, tire size, terrain, and load
Determine whether the axle is used in a 4×2, 6×2, or 8×2 vehicle
Identify the non-driven axle and load-transfer system in a 6×2 configuration
Determine whether the axle has a driver-controlled differential lock
Confirm housing wall thickness
Identify SelecTTrac equipment
Verify dual or wide-base single-tire compatibility
Confirm hub, bearing, spindle, brake, wheel, and tire specifications
Check suspension mounting dimensions and track width
Verify driveshaft and yoke compatibility
Inspect used gears for scoring, pitting, overheating, and abnormal wear
Inspect the housing for cracks, bending, corrosion, and damaged mounts
Check the pinion and wheel ends for lubricant leakage
Inspect axle shafts, yokes, splines, and universal joints
Request lubricant and maintenance records
Verify replacement-part availability
Obtain Dana or OEM approval for demanding applications
Include freight, core charges, lubricant, brakes, installation, and electronic calibration in the total cost

Variants and Configurations

S21-172 with a 21,000-pound GAWR
S23-172 with a 23,000-pound GAWR
S25-172 with a 25,000-pound GAWR
4×2 single-rear-axle configuration
6×2 pusher-axle configuration
6×2 tag-axle configuration
Spicer EconoTrek 6×2 configuration
8×2 configuration
Ratios from 3.07 through 6.14
Standard wheel differential
Driver-controlled wheel differential lock
Standard housing configuration
Heavy-wall housing configuration
Passive lubricant-management system
Dual-tire configuration
Wide-base single-tire configuration
SelecTTrac configuration
Drum-brake configuration
Air-disc-brake configuration
Linehaul configuration
Regional-haul configuration
Vocational configuration

Comparison to Similar Equipment

Compared with the Dana Spicer D172 Series, the S172 uses one powered axle rather than a tandem pair. This reduces weight and mechanical losses but provides less traction and lower combined axle capacity.

The D172 is better suited to construction, heavy haul, and severe vocational work requiring two powered rear axles. The S172 is better suited to weight-conscious 4×2, 6×2, and 8×2 applications.

Compared with the Dana Spicer S140 Series, the S172 serves heavier Class 7 and Class 8 vehicles. The S140 is primarily intended for medium-duty straight trucks, buses, and utility vehicles.

Compared with the Dana Spicer S190 Series, the S172 provides lower axle ratings and a lighter design. The S190 is intended for heavier vocational and severe-service applications.

Compared with the Dana Spicer AdvanTEK 40 Tandem Axle, an S172-based 6×2 system eliminates one powered axle. This can improve efficiency but reduces low-traction capability.

Best Fit For

Class 7 single-drive-axle trucks
Class 8 highway tractors
Linehaul fleets considering 6×2 drivetrains
Regional-haul operations
Weight-sensitive freight operations
Fuel-conscious fleets
Vehicles using a 4×2 configuration
Vehicles using a 6×2 tag axle
Vehicles using a 6×2 pusher axle
Vehicles using an 8×2 configuration
Applications requiring a 21,000-pound drive axle
Applications requiring a 23,000-pound drive axle
Applications requiring a 25,000-pound drive axle
Fleets operating primarily on paved roads
Operations with predictable axle loading
Applications needing an optional wheel differential lock

Related Truck Types

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

Related Truck Models

Related Axle and Differential Types

Related Equipment Systems

Related Guides

Regulatory and Compliance Notes

The S172’s 21,000- to 25,000-pound ratings describe the mechanical capacity of specific axle models. They do not automatically establish the legal rear axle weight of the truck.

Legal loading depends on federal, state, provincial, and local rules; axle spacing; tire and wheel ratings; suspension capacity; brake equipment; and the vehicle’s certified gross axle weight ratings.

In a 6×2 or 8×2 configuration, weight must remain properly distributed among the drive and non-driven axles. Load-transfer or lift systems must comply with applicable regulations.

Liftable or unloadable axles may be subject to controls governing when they can be raised, how much weight can be transferred, and whether they count toward legal axle spacing.

Changes to axle ratio, tire size, suspension controls, or axle loading can affect speedometer calibration, transmission programming, ABS, traction control, stability control, and emissions operation.

Real World Operating Notes

The S172 is most effective where fleets can benefit from reduced weight and mechanical losses without regularly needing the traction of a 6×4 tandem.

A 6×2 configuration generally performs best in linehaul and regional operations on paved roads with controlled loading.

Snow, mud, gravel, wet grass, loading ramps, and uneven surfaces can expose the traction limitations of having only one driven rear axle.

Proper tire selection, differential-lock use, and drive-axle loading can improve 6×2 performance in low-traction conditions.

The EconoTrek system’s potential weight and efficiency benefits depend on the complete vehicle specification, route, driving practices, cargo distribution, and maintenance.

A used S172 axle should be checked carefully for model, ratio, capacity, housing thickness, differential lock, brakes, wheel ends, track width, and suspension mounts.

Frequently Asked Questions

What is the Dana Spicer S172 Series?

The S172 Series is a family of heavy-duty single drive axles for Class 7 and Class 8 vehicles using 4×2, 6×2, and 8×2 configurations.

What models are included in the S172 Series?

The primary models are the S21-172, S23-172, and S25-172.

What is the S21-172 rated for?

The S21-172 has a maximum published gross axle weight rating of 21,000 pounds.

What is the S23-172 rated for?

The S23-172 has a maximum published gross axle weight rating of 23,000 pounds.

What is the S25-172 rated for?

The S25-172 has a maximum published gross axle weight rating of 25,000 pounds.

What is the maximum published nominal GCW?

Referenced Dana specifications list a nominal GCW of up to 100,000 pounds for S172 models. The final rating depends on the vehicle and application.

What ratios are available?

Dana identifies a ratio range from 3.07:1 through 6.14:1.

Can the S172 be used in a 6×2 truck?

Yes. It can be paired with a non-driven tag or pusher axle, including Dana’s EconoTrek 6×2 system.

What is the Spicer EconoTrek system?

EconoTrek combines an S172 drive axle with a non-driven tag axle to create a lighter and more efficient 6×2 rear-axle system.

Is EconoTrek lighter than a 6×4 tandem?

Dana has stated that the system can weigh up to approximately 380 pounds less than a typical 6×4 configuration.

Does the S172 have a differential lock?

An integrated driver-controlled wheel differential lock is available for improved traction and spinout protection.

Does the S172 have a power divider?

No. A power divider is used to distribute torque between two drive axles. The S172 is a single drive axle.

Is a 6×2 as good as a 6×4 in snow or mud?

Generally, a 6×4 provides better traction because both rear axles are powered. A properly loaded 6×2 with suitable tires, traction controls, and a differential lock can still perform well in many road applications.

Can the S172 use wide-base single tires?

Yes, in approved configurations. Dana’s SelecTTrac option supports dual or wide-base single-tire applications.

Can an S172 replace an S170?

Possibly, but it should not be treated as an automatic direct replacement. Mounting, ratio, yoke, suspension, brakes, hubs, track width, and OEM approval must be checked.

Availability and Where to Find

The Dana Spicer S172 Series is available through participating Class 7 and Class 8 truck manufacturers, Dana-authorized distributors, commercial truck dealers, drivetrain specialists, rebuilders, and aftermarket suppliers.

New and remanufactured carriers, gears, bearings, seals, differential components, axle shafts, wheel-end parts, and differential-lock components may be available separately.

Used complete axle assemblies may be available from heavy-truck recyclers. Buyers should verify the model, capacity, ratio, housing, track width, suspension mounts, brakes, wheel ends, differential lock, and overall condition.

Official specifications, product information, application guidance, and warranty resources are available from the Dana Spicer S172 Series product page and the Dana Resource Library.

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