For commercial truckers, power take-offs get real results. In one recent experiment, a fleet of 150 bucket trucks saved $443,000 in fuel costs and slashed CO₂ emissions by 788 tons in a single year—just by integrating electrical power take-offs (ePTOs).
Moreover, though ePTOs are the newest, trendiest devices on the block, old-school PTOs are still incredibly useful.
In the average vehicle with a typical, gasoline-fueled combustion engine, only 12%–30% of the energy it takes is used to power the driveline. The majority of the energy granted by the fuel is lost, inadvertently converted to unusable thermal energy.
The “excess” heat then dissipates, off-gassing as hot air from the engine, through exhaust pipes, or into the ground via the wheels (as friction heat).
Even the lowest-tech power take-offs stem this loss. PTOs capture a percentage of the energy output from a vehicle’s engine, transmission, or battery, then redirect it to a useful task: powering auxiliary equipment.
In this guide, learn how different types of PTOs work, their benefits and drawbacks, and how to choose and maintain the right PTO for your commercial HDV.
Power Take-Offs, Defined: PTO Function In Heavy-Duty Trucks
PTOs are energy redirection and conversion devices, built to integrate into a machine’s powertrain. They’re used in industrial machinery in manufacturing facilities, drivable agricultural machines like tractors, and vehicles—particularly Class 7 and Class 8 commercial trucks.
What Is a Power Take-Off In Machinery?
A power take-off is an assembly: a device composed of smaller components, working together to serve its function. The specific functions of a PTO are energy conservation, conversion, and direction.
WhatIs?, the technology resource guide by TechTarget, has a useful description. It defines “Power take-off (PTO)” as “a device that transfers an engine's mechanical power to another piece of equipment.”
Typically, only a portion of the engine’s energy output is transferred to the PTO’s recipient machinery.
The guide then explains, “A PTO allows the hosting energy source to transmit power to additional equipment that does not have its own engine or motor. For example, a PTO can help run a jackhammer using a tractor's engine."
In essence, a PTO is an assembly, like a gearbox, that enables an engine or motor to power more machines or systems than it otherwise could.
Unique Function of PTOs In HDV Drivetrains
When they’re integrated into commercial, heavy-duty vehicle powertrains, PTOs are used to power auxiliary equipment integrated in the HDV.
Auxiliary equipment is any functional, mechanical parts of a vehicle unrelated to driving, yet typically necessary for the HDV to serve its function. Thus, for commercial HDVs, a PTO can effectively empower:
Open-box beds of dump trucks
Tow truck winches (automatic cables)
Hydraulic pumps and lifts for construction attachments
Vacuums
Rotating mixer drums on cement or concrete trucks
Electrical generators for refrigeration units (cold transport)
Snow plow machinery
Sprayers, rotary brooms, and hoppers on street sweeper trucks
With a power take-off, each of these mechanical add-ons can function effectively, solely using energy sources already built into the truck—its engine, transmission, or battery.
How Does A PTO Work In A Heavy-Duty Truck?
In a heavy-duty truck, a PTO redirects power from either the truck’s engine, transmission, or battery, to auxiliary equipment or machinery.
Different PTOs use distinct energy transfer mechanisms. To receive and route the energy, most PTOs use one of four mechanisms:
Physical, rotational mechanisms (i.e. non-synchronous gearbox components), which redirect the mechanical energy without converting it.
Hydraulic mechanisms, which convert mechanical energy into hydrostatic energy before transferring it.
Electromagnetic induction mechanisms, specific to PTOs that convert mechanical energy into electricity (like a generator).
Electrical conversion and transmission mechanisms, which invert and transform the electrical output from a truck's battery or an EV's motor into a usable A/C current, then use that current to power equipment.
Only electrical power take-off (ePTO) devices use electrical conversion.
Differentiating Power Take-Offs: Types & Categories
Short Duration Vs. Continuous Operation
Some PTOs are designed to continually deliver energy to the equipment as long as the commercial truck is running. Others engage and disengage independently of the HDV’s engine, only delivering energy to equipment when activated.
Short-Duration PTOs (Independent / Intermittent)
Short-duration power take-offs, also called independent PTOs, are not engaged at all times. Instead, they can be engaged and disengaged as needed, either manually (by the vehicle’s operator), or automatically in response to operating/use conditions. They’re sub-categorized by the type of shift used to engage or disengage the device, with two-stage clutch mechanisms among the most popular independent PTOs.
These devices are designed to transfer power to auxiliary equipment in short increments. Typically, short-duration PTOs deliver bursts of energy for five minutes or fewer in a 15-minute span.
If energy is meant to be routed in a predictable pattern of short bursts, the device might be called an intermittent PTO. Tow trucks, dump trucks, and truck-mounted aerial work platforms are more likely to use an independent PTO.
Continuous PTOs (Live / Constant Drive)
Continuous PTOs, also called “constant drive” or “no-clutch” power take-offs, are always engaged. Their function is wholly aligned with the vehicle’s engine. If the truck is on, so is the PTO.
These devices are best for powering equipment for extended periods, and they're all but necessary for non-stop applications. Constant drive PTOs are best for street sweepers, snow plows, garbage trucks, and similarly utilitarian HDVs.
PTO Shift Types
Power take-offs can be categorized by shift type. Most PTOs are mechanical (manual) shifts, which use a lever or compressed air mechanism to physically shift gears in the PTO's non-synchronous gearbox.
Other PTOs are clutch shifts (also called “power shifts” or “hot shifts”). Clutch shifts are semi-automated, and they’re used in short-duration applications.
More rare are non-shifting, constant drive PTOs. These power take-offs constantly feed power from the engine to auxiliary machinery, even when the HDV isn't in motion.
PTO Engagement Mechanism Categories
PTO engagement is the feature or mechanism that activates the power take-off, initiating its energy transfer. Among PTOs used in commercial vehicles, four engagement mechanisms are common.
Mechanical (Lever Or Switch) Activation
Mechanical PTOs utilize diverse engagement components, including sliding gears and mesh, rubber blocks, loaded springs, a manually operated lever or pedal, or mechanical cable links.
Hydraulic / Hydrostatic Pressure Mechanisms
Hydraulic features apply pressure to the device’s control valve, engaging the clutch. Once engaged, the clutch connects the PTO shaft to the engine.
Pneumatic (Air Valve) Mechanisms
Like hydraulics, air compression mechanisms apply pressure to engage the clutch, and alleviate pressure to disengage.
Electromagnetic Solenoid Engagement (Activated By Electrical Sensors)
Solenoids are the components of ePTOs that regulate engagement in response to the drivetrain.
PTO Types By Mount Placement
Commercial trucks and HDVs are typically compatible with six PTO mount types. Three attach to the drivetrain's transmission, and three mount the engine's crankshaft.
Transmission-Mounted PTOs: Side-Mount, Top-Mount & Rear-Mount
Side-mount PTOs mesh with the gear of the transmission. Integrate these devices with the drivetrain by bolting them to the transmission’s side or underside. Whether side-mounting or bottom-mounting is correct depends on your specific vehicle’s attachment setup.
Top-mount PTOs are typically compact devices with splined countershaft extensions, designed to attach to the top of the transmission.
Rear-mount PTOs are similar, though they specifically connect to the transmission’s rear countershaft. They’re the standard power take-off in Europe, and they’re used for fire trucks in the U.S.
Engine-Mounted PTOs: Rear-Mount, Front-Mount & Split-Shaft
Engine-mount PTOs are attached to the engine directly, receiving energy and engagement directly from its crankshaft. These devices are further categorized as rear-engine-mount, front-engine mount, and engine flywheel (“sandwich”) mounts, as different designs attach to different points along the crankshaft.
Split-Shaft PTOs are sometimes categorized separately, as “sandwich” devices. They’re positioned in between the engine and the transmission.
Split-shaft PTOs integrate a second transmission mechanism, letting the device split its energy draw between the two. This helps balance the PTO's energy use, preventing it from inadvertently causing the engine to stall as it fulfills high-power demands.
Understanding PTO Specs & Requirements
Power take-offs differ in their relative capacities to deliver energy to equipment, and the kind of demands they put on engines. To choose a compatible PTO for your HDV, it’s important to understand how the device is rated, and what those ratings mean.
PTOs are rated by torque capacity, horsepower, service factor, and speed. To find the right one, first, look up the relevant specifications of the transmission model you plan to mount the PTO on. Then, choose a PTO with the capacity to easily manage the transmission's output.
Torque Capacity
Torque is the engine’s rotational (mechanical) force, output by the crankshaft, the transmission flywheel, or the gearbox. Torque indicates the strength of output force (measured in newtons), multiplied by the radius vector of a point orbiting an axis.
The higher an engine's energy output (power), the greater the torque force of its rotating mechanisms, and the faster they rotate. The rotational speed of an engine or powertrain is measured in its relevant components' revolutions per minute (RPM).
A PTO’s torque capacity rating indicates how much twisting force it can handle without accruing damage. It’s typically expressed in Newton-metres (N·m). In general, the higher a power takeoff's torque capacity rating, the heavier loads it can handle, and the greater demands it can fulfill.
Horsepower
An engine's power is measured in horsepower (HP). Calculate HP by multiplying the engine's torque by its RPM, then dividing by a constant.
Every contemporary commercial truck model comes with a PTO horsepower rating. It tells you exactly how much horsepower is available to a PTO at the recommended mount point (a percentage of the engine’s full HP) at an industry-standard RPM.
A PTO must be capable of delivering the amount of power the auxiliary equipment needs to function while withstanding the engine's torque force. The PTO's rating tells you how much energy it can deliver at a given RPM (expressed as a ratio).
So, if the industry-standard RPM for engine class is 1000, a PTO rated 60 HP can deliver, at most, 60 units of horsepower to the equipment while the engine is running at 1000 RPM.
Service Factor
A PTO's service factor is a multiplier. Take the engine's rated torque force output, then multiply it by the service factor value relevant to your intended applications.
The SFV of heavy-duty applications is 2.0. Thus, the right PTO for the job needs a torque capacity ≥ the product of the HDV engine’s torque output x2.
Speed
A power take-off’s speed is the RPM of its shaft. This indicates the speed at which it transfers energy to the auxiliary equipment, and how much energy it can transfer effectively.
Most PTOs are designed to run at an industry-standard speed for applications in a given category. PTOs built for heavy-duty applications typically run at 1000 RPM or 1300 RPM.
High-Impact PTO Applications For Class 7 & 8 Trucks
Power take-offs can be used to run powerful, high-impact equipment from your truck's engine. Cranes, cargo-hauling machinery, water pumps, and hydraulic backhoes can operate solely on the energy redirected from your truck's engine with a PTO.
The most energy-efficient applications run oft-stationary work trucks like bucket lifts. Statistically, these types of vocational work trucks only drive four hours a day (or fewer). With a PTO, the engine doesn’t need to be left idling when it’s not driving and the equipment’s in use.
New, innovative models of automated manual transmission (AMT) drives for heavy-duty trucks feature dual-PTO options. The Mack mDRIVE AMT system, for example, is dual-PTO compatible. More than that, though, it incorporates clutched adapters, multi-point mounts, and flange connections, with independent, right- and left-side dash switches.
Like many modern AMT transmissions, these adaptive dual-PTO drivetrains use an air solenoid to automate the direction of power.
Altogether, these inventions deliver smoother shifts and greater efficiency for Class 7 and Class 8 HDVs.
Power Take-Off Trouble: Signs, Symptoms & Troubleshooting
Your HDV’s power take-off might be in trouble if you’re experiencing certain warning signs. Stay alert to symptoms, which may include your truck shaking or rattling, slipping gears, grinding sounds, excessive heat, a burning smell, and any trouble engaging or disengaging the PTO’s lever.
Once you suspect a problem, work systematically to diagnose your vehicle.
Diagnostic Inspections & Tests
First, perform a thorough visual, scent, and auditory inspections. For the visual inspection, follow the circuit of your truck’s powertrain, drivetrain, and PTO components. Use the schematics for your vehicle for comparison.
Be sure to visually note and assess:
Switch / lever friction, alignment
Wiring harness (mount)
Damage to or loss of mount fasteners
Drive belt damage or warping
Any chipping, rusting, or melding of gear teeth, splines, or the output shaft
Illuminated or flashing indicator light(s) on the dashboard
Visible leaks of transmission fluid or hydraulic fluid
Discolored hydraulic fluid
By sound and scent inspection, observe any warning signs. These might include:
Excessive noise (grinding, rattling, or clattering vibrations)
High-pitched whining sounds (escaping air)
Dripping sound (fluid leaks)
Burning smell
Gather quantitative data and test your transmission’s functionality by:
Validating electrical current terminal voltage
Analyzing the air pressure (PSI)
Measure temperature with an infrared thermometer
Check transmission oil for discoloration or debris
Verify PTO capacity and current operational load
Checking the lever’s engagement and disengagement
Dysfunctional PTO Solutions
Once you've honed in on the underlying cause of your PTO's problems, you can start to solve it. Jammed components and rickety clutches often call for greater lubrication—particularly if any lubricant has leaked.
Be sure to check the strength of any battery you’re using, and replace any broken or damaged points of connection.
If a more significant component of your drivetrain system needs to be replaced you fix your PTO, that’s very doable. But, it’s best to do it when aided by a professional technician.
Power Take-Off Care & Repair
An HDV’s power take-off needs regular maintenance to stay in optimal shape. This checklist offers a solid run-down of daily, weekly, and semi-annual maintenance tasks to keep your PTO clean and effective.
Commercial Truck & Automotive PTO Maintenance Checklist
Check mounting bolts within 1-2 weeks of installation (look for accurate vs. inappropriate torque)
Secure all bolts, harnesses, and fasteners daily (or weekly, if the PTO is infrequently used)
Check pressure gauge readings of hydraulic and pneumatic PTOs daily
Monitor system pressure and flow rates daily when using a continuous / live PTO
Inspect gaskets, seals, and tubing for signs of leaks, and replace the relevant component as soon as any are found
After the first 100 hrs, inspect for fraying and leaks due to friction (pressure)
Schedule physical maintenance at more frequent intervals if you observe unusual wear patterns.
Clean and grease the splines directly connecting to the PTO 1-4x per month
Regularly inspect the clutch assembly visually, and realign its engagement / disengagement points as needed
Change the PTO’s filter every 500 hours of use, or as frequently as the manufacturer recommends
Change PTO lubricant during regular oil changes (every 25k miles for most heavy-duty trucks)
How To Choose The Best Power Take-Off For Your Heavy-Duty Truck (PTO Buying Guide)
Use the manufacturer’s specifications for your truck and auxiliary equipment to determine the functional parameters your PTO must meet.
Fit & Function
Consider whether the equipment’s operation is for extended durations or only in short bursts. Typically, you’ll want to discern:
Output Speed
Input Speed Capacity
Horsepower
Torque Capacity
Service Factor
Live Vs. Independent PTO Integration
You’ll also want to determine the space available on or around your HDV’s powertrain to safely mount the PTO. Choose a device compact enough to fit into the mounting space easily. Be sure the power take-off’s mechanisms are oriented in a direction compatible with the vehicle’s crankshaft or transmission.
Manual Vs. Automatic
If the PTO is independent, consider the degree of personal control you want over the engagement and operation of the energy transfer. Manual clutch activation is hands on, while automated electronic or hydraulic systems offer smoother experiences.
Consider Reputation
Finally, seek out recommendations from other trucking professionals you respect in your field. Which manufacturers have a reputation for quality among unbiased reviewers.
As you compare PTO brands, weigh factors like available warranties, the typical availability and competence of support services, and your efficiency goals before making the final call.
Installing a Power Take-Off In Your HDV: Tactics & Safety Tips
Installing a power take-off is a complex process best handled by a certified HDV automotive technician.
Installation should adhere to the manufacturer's instructions, and to guidelines established by the Society of Automotive Engineers (SAE).
Most importantly, any procedure to install a power take-off on a heavy-duty truck to meet or exceed the relevant safety standards established by the International Standards Organization (ISO). These include ISO 7653:1985 and ISO 5673-1:2005.
These standards establish crucial baselines for ground clearance, shielding, best mounting practices, and many other vital measurements.
Once you’ve made sure to engage in best practices by sticking strictly to the detailed processes, you can install or repair your PTO. When you do, keep these safety tips in mind at all times:
Do not wear loose clothes, jewelry, or “down” hair
Disengage the PTO before turning on the power source
Double-check RPM ratings of all systems, sources, and equipment. Do NOT connect devices or components with divergent RPMs.
Operate PTO shafts at moderate angles.
Secure and maintain safety shields on equipment at all times
Ensure free rotation of spinner shields
Get The Right Power Take-Off For Your HDV At Point Spring
At Point Spring & Driveshaft Co., our certified technicians work with you, for you. Discover the just-right PTO to boost your heavy-duty truck’s efficiency. Or, keep your truck running steady with our regular maintenance services.
Ready to get started? Fill out the form below, or call us at 888-787-7746. We’re happy to help.