PACCAR TX-18 Transmission

Quick Facts

Manufacturer: PACCAR
Transmission Type: Heavy-Duty Automated Manual Transmission
Transmission Family: PACCAR TX Series
Primary Configuration: 18-Speed Overdrive
Forward Speeds: 18
Reverse Speeds: Three
Maximum Engine Torque: 1,850 lb-ft
Maximum Engine Horsepower: 510 horsepower
Maximum Operating Weight: 140,000 pounds GCWR
Overall Ratio: 20.46:1
First-Gear Ratio: 14.32:1
Top-Gear Ratio: 0.70:1 Overdrive
Clutch Type: Maintenance-Free Self-Adjusting Diaphragm-Spring Clutch
Clutch Control: Electronic Clutch Actuator
Clutch Pedal: No
PTO Openings: Standard 8-Bolt Bottom and 4-Bolt Rear
Combined PTO Capacity: 160 horsepower and 610 lb-ft of torque
PTO Speed: Approximately 111 percent of engine speed
Compatible Engines: PACCAR MX-11 and PACCAR MX-13
Approximate System Weight: 808 pounds including transmission, clutch, and oil
Oil Capacity: Approximately 25.4 pints in a cooler-less, non-PTO configuration
Recommended Lubricant: PACCAR-approved transmission lubricant meeting the applicable specification
Maximum Oil-Change Interval: Up to 500,000 miles or five years in approved on-highway applications
Primary Applications: Heavy On-Highway Hauling, Equipment Transport, Tankers, Construction, Regional Heavy Haul, and High-Performance Class 8 Trucks
Production Status: Active Production

Overview

The PACCAR TX-18 is an 18-speed automated manual transmission designed for heavy-duty on-highway, vocational, and heavy-haul applications.

It is integrated with PACCAR MX-11 and MX-13 engines and offered in selected Kenworth and Peterbilt Class 8 trucks.

The TX-18 provides substantially greater ratio coverage than the 12-speed PACCAR TX-12. Its 18 closely spaced forward gears help keep the engine within an effective operating range while accelerating heavy combinations, climbing grades, and responding to changing road conditions.

The transmission supports engines producing up to 510 horsepower and 1,850 lb-ft of torque. Its maximum published operating weight is 140,000 pounds GCWR.

Three reverse gears provide additional control when backing equipment trailers, tankers, construction vehicles, and other heavy combinations.

The TX-18 uses twin-countershaft construction, helical gears, large bearings, precision lubrication, an electronic clutch actuator, a self-adjusting clutch, dual PTO openings, and internal wiring and sensors.

The standard TX-18 is intended primarily for high-performance on-highway operation. The related TX-18 Pro adds an Extreme Duty clutch, additional reverse gears, Rock Free mode, and more specialized off-highway capabilities.

Key Characteristics

The TX-18 has a 20.46:1 overall ratio spread.

Its 14.32:1 first gear supports loaded starts, while the 0.70:1 eighteenth gear provides overdrive highway operation.

Most ratio changes are approximately 19 or 20 percent. These relatively small and consistent steps help maintain engine speed when the truck is heavily loaded.

The transmission uses twin-countershaft construction with helical gears and large bearings designed for higher torque and operating weights.

Internal wiring and sensors reduce exposure to road spray, corrosion, loose connections, and physical damage.

The transmission’s Precision Lubrication System directs lubricant to critical gears and bearings while reducing oil-churning losses.

Two standard PTO openings support hydraulic pumps, product-handling systems, blowers, cranes, winches, and other vocational equipment.

The TX-18 is approximately 225 pounds lighter than comparable older 18-speed UltraShift PLUS configurations, according to PACCAR’s related transmission design information.

How the Transmission Works

The PACCAR TX-18 uses a mechanical twin-countershaft geartrain combined with electronic controls, shift actuators, and an electronically operated dry clutch.

When the driver selects drive, the transmission controller evaluates vehicle weight, road grade, engine torque, throttle position, vehicle speed, and the selected operating mode.

The controller chooses an appropriate starting gear and commands the electronic clutch actuator to engage the clutch.

During acceleration, the transmission determines whether every gear is required. It can skip gears when the truck is lightly loaded or use smaller gear steps under heavier conditions.

Before shifting, the transmission requests a reduction in engine torque. This unloads the drivetrain and allows the current gear to disengage.

The shift actuator selects the next ratio while the engine and transmission controllers coordinate shaft speed and engine RPM.

When the next gear is engaged, engine torque is restored.

Hill Start Aid uses the truck’s foundation brakes to help prevent rollback when launching on a grade.

Urge to Move allows the truck to inch forward when the service brake is released.

Creep Mode provides controlled low-speed movement at engine idle with the clutch locked.

Enhanced Engine Braking commands downshifts when additional engine-brake performance is needed.

Predictive or terrain-aware shift strategies can prepare the transmission for upcoming road conditions when the truck is properly equipped.

Common Specifications

Transmission Type

The PACCAR TX-18 is a two-pedal automated manual transmission.

It uses a mechanical geartrain and dry clutch rather than the torque converter and planetary gearsets used in a conventional automatic transmission.

Forward Speeds

The transmission provides 18 forward gears.

These gears are separated by relatively small ratio steps to improve acceleration and grade performance under heavy loads.

Reverse Speeds

The standard TX-18 provides three reverse gears.

Published reverse ratios are:

Reverse 1 — 15.25:1
Reverse 2 — 12.73:1
Reverse 3 — 10.67:1

The TX-18 Pro can provide as many as six reverse gears, but the additional high-speed reverse ratios are not part of the standard TX-18 configuration.

Forward Gear Ratios

First Gear — 14.32:1
Second Gear — 11.96:1
Third Gear — 10.02:1
Fourth Gear — 8.43:1
Fifth Gear — 7.04:1
Sixth Gear — 5.90:1
Seventh Gear — 4.95:1
Eighth Gear — 4.13:1
Ninth Gear — 3.46:1
Tenth Gear — 2.89:1
Eleventh Gear — 2.41:1
Twelfth Gear — 2.02:1
Thirteenth Gear — 1.70:1
Fourteenth Gear — 1.42:1
Fifteenth Gear — 1.19:1
Sixteenth Gear — 1.00:1 Direct Drive
Seventeenth Gear — 0.83:1 Overdrive
Eighteenth Gear — 0.70:1 Overdrive

Overall Ratio

The overall ratio spread is approximately 20.46:1.

This provides strong startability while retaining a tall overdrive ratio for highway operation.

Maximum Engine Torque

The maximum published engine-torque capacity is 1,850 lb-ft.

The PACCAR MX engine must be programmed within the approved transmission rating.

Maximum Engine Horsepower

The maximum published engine output is 510 horsepower.

Horsepower alone does not establish compatibility. Torque, governed speed, software, cooling, GCWR, and vehicle application must also be approved.

Maximum Operating Weight

The TX-18 has a maximum published operating weight of 140,000 pounds GCWR.

This transmission rating does not override the truck’s GVWR, axle ratings, tire ratings, fifth-wheel capacity, trailer ratings, or legal weight limits.

Clutch System

The standard TX-18 uses a maintenance-free, self-adjusting diaphragm-spring clutch.

An electronic clutch actuator controls engagement and disengagement.

The TX-18 Pro uses an Extreme Duty clutch for increased thermal capacity and off-highway maneuvering.

Transmission Controls

The transmission control system manages:

Starting-gear selection
Clutch engagement
Upshifts and downshifts
Skip shifting
Engine-torque coordination
Hill Start Aid
Urge to Move
Creep Mode
Engine overspeed protection
Enhanced engine braking
Manual gear requests

Column-Mounted Selector

Kenworth and Peterbilt installations commonly use a right-hand column-mounted selector.

The selector can provide:

Drive
Neutral
Reverse
Manual Mode
Low Mode
Upshift and downshift requests
Engine-brake controls depending on truck configuration

Twin-Countershaft Design

The TX-18 divides engine torque through two countershafts.

This construction helps distribute internal loads while supporting high engine torque and heavy vehicle weights.

Helical Gears

Helical gears help improve smoothness and reduce operating noise compared with many traditional straight-cut heavy-duty transmission gears.

Internal Wiring and Sensors

Internal wiring and sensor placement reduce exposure to corrosion, moisture, road debris, and physical damage.

The transmission includes fluid-pressure and oil-temperature monitoring to identify potentially damaging conditions.

PTO Openings

The TX-18 provides two standard PTO mounting locations:

8-bolt bottom opening
4-bolt rear opening

Both PTO drives operate at approximately 111 percent of engine speed.

PTO Capacity

Maximum combined PTO output is:

160 horsepower
610 lb-ft of torque

The total load of all simultaneously operating PTO equipment must remain within the combined limit.

Precision Lubrication

The Precision Lubrication System directs lubricant to gears and bearings.

This reduces unnecessary lubricant churning and can improve transmission efficiency.

Oil Capacity

A cooler-less, non-PTO configuration holds approximately 25.4 pints of lubricant.

Actual capacity can change with PTOs, cooling equipment, installation angle, and truck configuration.

Oil-Change Intervals

Published maximum service intervals include:

On-Highway — 500,000 miles or five years
Vocational — 250,000 miles or three years

Actual maintenance requirements depend on application and operating conditions.

Transmission Cooling

A transmission cooler may not be required in approved configurations operating below 110,000 pounds GCW.

Heavier, high-temperature, PTO-intensive, or severe applications may require additional cooling.

System Weight

The TX-18 system weighs approximately 808 pounds, including the transmission, clutch, and oil.

Additional PTOs, pumps, cooling equipment, mounts, and driveshaft components increase installed weight.

Common Applications

Heavy on-highway hauling
Regional heavy haul
Equipment-hauling tractors
Lowboy and RGN operations
Tanker transportation
Unbaffled milk tanker operations
Grain hauling
Livestock hauling
Construction trucks
Block trucks
Refuse roll-off trucks
Mobile-crane trucks
Wrecker and recovery vehicles
Double-trailer operations
High-performance highway tractors
Mixed highway and vocational service

Truck and Engine Compatibility

The PACCAR TX-18 is designed for integration with PACCAR MX engines and selected Kenworth and Peterbilt Class 8 trucks.

Confirmed Kenworth applications with live Truck Equipment Atlas pages include:

The TX-18 and TX-18 Pro were introduced as available options in the Kenworth T680, T880, and W990.

Confirmed Peterbilt applications with live pages include:

Transmission availability depends on model year, engine selection, torque rating, truck configuration, market, and vocation.

Compatible engine families include:

The engine and transmission communicate as an integrated PACCAR powertrain.

The TX-18 is not normally paired with Cummins, Detroit, Volvo, Mack, or International engines. Those engines use other automated manual transmission families.

Advantages

18 forward gears
Three reverse gears
Maximum torque capacity of 1,850 lb-ft
Supports engines up to 510 horsepower
Maximum GCWR of 140,000 pounds
Closely spaced gear ratios
Deep 14.32 first gear
0.70 overdrive top gear
Strong heavy-load performance
Automated clutch and gear selection
No clutch pedal
Self-adjusting clutch
Hill Start Aid
Urge to Move
Creep Mode
Smart starting-gear selection
Skip-shift capability
Enhanced engine braking
Integrated PACCAR engine controls
Dual PTO openings
Maximum combined PTO output of 160 horsepower
Precision Lubrication System
Internal wiring and sensors
Fluid-pressure and temperature monitoring
Lower weight than comparable older 18-speed automated transmissions

Limitations or Considerations

Primarily limited to Kenworth and Peterbilt trucks
Designed specifically for PACCAR MX engines
Maximum torque is limited to 1,850 lb-ft
Maximum operating weight is 140,000 pounds
Not intended for applications requiring unlimited GCW
Only three reverse gears
Does not include TX-18 Pro’s high-speed reverse capability
Standard clutch is not the Extreme Duty Pro clutch
Electronic controls require specialized diagnostics
Clutch-actuator service requires calibration
A transmission cooler may be required in heavier applications
PTO equipment adds weight and maintenance
Low-speed maneuvering can create clutch heat
Truck and engine software must remain compatible
Higher purchase cost than lighter highway transmissions

Driver and Operator Experience

The TX-18 provides two-pedal operation without a clutch pedal.

The driver selects drive, neutral, reverse, manual, or low mode using the column-mounted selector.

The transmission chooses an appropriate starting gear based on vehicle weight, grade, throttle demand, and engine torque.

Hill Start Aid helps prevent rollback during loaded launches on grades.

Urge to Move allows the truck to begin inching after the brake is released.

Creep Mode provides low-speed movement at engine idle with the clutch locked.

The 18 forward ratios allow the transmission to make smaller changes in engine speed than a 12-speed transmission.

The transmission can skip gears when lightly loaded rather than shifting through all 18 ratios.

Manual mode allows the driver to request or hold a gear when approaching a grade, descending with the engine brake, entering a construction area, or preparing for changing road conditions.

The controller may refuse a requested shift that could over-speed or lug the engine.

Maintenance and Ownership Notes

The TX-18 uses PACCAR-approved transmission lubricant.

A cooler-less, non-PTO configuration holds approximately 25.4 pints.

The maximum on-highway oil-change interval is up to 500,000 miles or five years.

Vocational applications use a shorter maximum interval of approximately 250,000 miles or three years.

Fluid-pressure and oil-temperature warnings should be investigated immediately.

The self-adjusting clutch does not require normal manual adjustment, but clutch wear, heat events, and actuator condition must still be monitored.

The transmission control module, electronic clutch actuator, speed sensors, internal wiring, external connectors, power supply, and vehicle data network require compatible diagnostic procedures.

PTO mounting, pumps, seals, hydraulic lines, controls, and driven equipment should be inspected regularly.

A transmission cooler, if installed, adds hoses, fittings, and heat-exchanger components to the maintenance program.

Common Transmission Problems

Transmission Will Not Engage a Gear

Possible causes include low battery voltage, an electronic clutch-actuator fault, speed-sensor failure, low air pressure, an active fault code, communication problems, or internal damage.

Electronic Clutch Actuator Faults

Actuator failure, wiring damage, incorrect calibration, clutch wear, or excessive heat can interfere with launches and shifting.

Clutch Overheating

Repeated creeping, prolonged backing, holding the truck on a grade with the accelerator, or operating above approved weight can overheat the clutch.

Harsh or Delayed Shifts

Shift-quality problems may result from software, sensor faults, engine communication, unsuitable calibration, clutch problems, or driveline issues.

Transmission Stuck in Neutral

The transmission may remain in neutral when it cannot verify gear position, complete a shift, match shaft speeds, or communicate with the engine controller.

Fluid-Pressure Warning

A pressure warning may indicate low lubricant, leakage, incorrect fluid, an internal lubrication problem, or sensor failure.

Transmission Overheating

High GCW, steep grades, heavy PTO use, low-speed operation, inadequate cooling, or low lubricant can increase temperature.

PTO Engagement Problems

PTO engagement may be prevented by incorrect conditions, failed interlocks, programming problems, hydraulic overload, or an active transmission fault.

Vehicle Data-Network Faults

Communication failures between the engine, transmission, brakes, and truck controllers can affect shifting and driver-assistance functions.

Oil Leaks

Leaks can occur at PTO openings, case joints, output seals, sensor locations, or cooler connections.

Buying Considerations

Confirm that the transmission is the standard TX-18 rather than TX-18 Pro.
Verify the truck is an approved Kenworth or Peterbilt model.
Confirm PACCAR MX-11 or MX-13 compatibility.
Verify the engine’s horsepower and torque.
Confirm the maximum operating GCWR.
Determine whether three reverse gears meet the application’s requirements.
Compare rear-axle ratio and tire size with the transmission gearing.
Calculate required PTO horsepower and torque.
Determine whether one or both PTO openings are needed.
Confirm whether a transmission cooler is required.
Review clutch-life and heat-event information.
Scan for active and inactive fault codes.
Inspect the electronic clutch actuator.
Verify software and calibration status.
Test Hill Start Aid.
Test Urge to Move and Creep Mode.
Road-test automatic and manual operation.
Test all reverse gears.
Review lubricant-service records.
Confirm PACCAR dealer and warranty support.

Variants and Configurations

PACCAR MX-11 Configuration
PACCAR MX-13 Configuration
Three-Reverse-Gear Configuration
8-Bolt Bottom PTO Configuration
Dual-PTO Configuration
Cooler-Less Configuration
Transmission-Cooler Configuration
Heavy On-Highway Configuration
Regional Heavy-Haul Configuration
Equipment-Hauler Configuration
Tanker Configuration
Grain-Hauler Configuration
Livestock-Hauler Configuration
Construction Configuration
Wrecker and Recovery Configuration
Kenworth Configuration
Peterbilt Configuration

Comparison to Similar Equipment

Compared with the PACCAR TX-12, the TX-18 provides six additional forward gears, three reverse gears, closer ratio spacing, greater heavy-load flexibility, and higher-capacity PTO equipment. The TX-12 is lighter and better suited to conventional highway service.

Compared with the PACCAR TX-12 Pro, the TX-18 supports higher GCW and provides 18 forward gears. The TX-12 Pro has an Extreme Duty clutch and vocational features for operations at or below 70,000 pounds.

Compared with the PACCAR TX-18 Pro, the standard TX-18 is more highway-oriented and uses three reverse gears. TX-18 Pro adds an Extreme Duty clutch, as many as six reverse gears, Rock Free mode, and off-highway programming.

Compared with Eaton Cummins Endurant XD, the TX-18 uses closely related transmission architecture but is integrated with PACCAR MX engines and PACCAR-branded trucks. Endurant XD is commonly paired with the Cummins X15 and other approved powertrains.

Compared with an Eaton Fuller 18-speed manual, the TX-18 automates clutch engagement and gear selection. The manual provides direct driver control, while the TX-18 reduces workload and standardizes shifting.

Compared with an Allison 4000 Series automatic, the TX-18 uses a dry clutch and mechanical geartrain rather than a torque converter. Allison offers smoother continuous low-speed power, while the TX-18 provides 18 ratios and strong mechanical efficiency.

Best Fit For

Kenworth heavy-duty fleets
Peterbilt heavy-duty fleets
PACCAR MX-11-powered trucks
PACCAR MX-13-powered trucks
Regional heavy-haul carriers
Equipment-hauling operations
Lowboy and RGN carriers
Tanker fleets
Grain haulers
Livestock carriers
Construction operations
Wrecker and recovery fleets
Applications below 140,000 pounds GCWR
Fleets wanting automated 18-speed operation
Drivers needing closely spaced ratios without manual shifting

Related Truck Types

Related Truck Models

Related Engines

Related Transmission Types

Related Equipment Systems

Electronic Clutch Actuators
Self-Adjusting Clutches
Transmission Electronic Controls
Vehicle Data Networks
Transmission Lubrication Systems
Transmission Cooling Systems
Transmission Diagnostic Systems
Electrical Systems
Driveshafts
Axles and Differentials
PTO Systems
Brake Systems

Related Guides

Understand the operating principles in How Commercial Truck Transmissions Work, compare drivetrain designs in Manual vs Automated Manual vs Automatic Transmissions, and evaluate gearing, application, and compatibility in How to Choose a Commercial Truck Transmission.

Regulatory and Compliance Notes

The TX-18 must be installed in a PACCAR-approved Kenworth or Peterbilt powertrain configuration.

The engine’s programmed torque must not exceed the transmission’s 1,850-lb-ft rating.

The completed truck must remain within the TX-18’s 140,000-pound maximum operating-weight rating.

The truck must also remain within its GVWR, axle ratings, tire ratings, frame limits, suspension ratings, fifth-wheel capacity, and trailer ratings.

PTO equipment must remain within the combined 160-horsepower and 610-lb-ft limits.

Changes to the engine, axle ratio, tire size, transmission software, or electronic controls can affect shifting, speedometer accuracy, engine braking, and emissions-system communication.

Oversize and overweight movements remain subject to permits, route restrictions, bridge laws, axle-spacing requirements, signs, flags, and other regulations.

Real World Operating Notes

The TX-18’s closely spaced ratios are most useful when the truck operates at higher gross weights or encounters frequent changes in grade.

The transmission can skip gears when the vehicle is lightly loaded and use smaller steps when additional pulling power is needed.

Three reverse gears provide more backing control than many highway automated transmissions.

The 0.70 overdrive top gear must be matched carefully with rear-axle ratio, tire size, engine cruising speed, and expected operating weight.

Creep Mode improves low-speed control, but prolonged clutch slipping should still be avoided.

The standard TX-18 is intended primarily for on-highway heavy-duty operation. Fleets spending substantial time off highway should compare it with the TX-18 Pro.

Frequently Asked Questions

What is the PACCAR TX-18?

It is an 18-speed automated manual transmission designed for PACCAR MX-powered Kenworth and Peterbilt heavy-duty trucks.

How much torque can it handle?

The maximum published torque capacity is 1,850 lb-ft.

What is its maximum operating weight?

The maximum published operating weight is 140,000 pounds GCWR.

How many reverse gears does it have?

The standard TX-18 has three reverse gears.

Does it have a clutch pedal?

No. An electronic clutch actuator operates the self-adjusting dry clutch.

What engines work with the TX-18?

The transmission is designed for integration with PACCAR MX-11 and MX-13 engines.

Which trucks offer the TX-18?

Documented applications include the Kenworth T680, T880, and W990 and the Peterbilt 389, 567, and 579.

Can it operate two PTOs?

Yes. It has standard 8-bolt bottom and 4-bolt rear PTO openings with a combined maximum capacity of 160 horsepower.

What is the difference between TX-18 and TX-18 Pro?

TX-18 Pro adds an Extreme Duty clutch, up to six reverse gears, Rock Free mode, and off-highway programming.

How often is the transmission oil changed?

The maximum published interval is up to 500,000 miles or five years for approved on-highway applications and 250,000 miles or three years for vocational service.

Availability and Where to Find

The PACCAR TX-18 is available through participating Kenworth and Peterbilt commercial truck dealers.

It can be ordered in approved PACCAR MX-powered truck configurations, including selected Kenworth T680, T880, and W990 models and Peterbilt 389, 567, and 579 models.

Availability depends on model year, truck configuration, engine rating, vocation, GCWR, PTO requirements, and market.

Current specifications, resources, shift calibrations, warranty information, and dealer availability can be confirmed through the official PACCAR TX-18 page.

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