What Is a PTO (Power Take-Off) on a Truck?
A PTO, or power take-off, is a small gearbox that bolts to an opening on the side of a truck’s transmission and sends engine power to equipment other than the drive wheels. It runs the hydraulic pump that lifts a dump body, drives a wet kit, turns a mixer drum, or powers a winch, blower or generator. The PTO is engaged only when that equipment is needed and sits idle the rest of the time.
What does a PTO do on a truck?
A vocational truck has to do work as well as move, and the PTO is how one diesel engine does both. It raises the hoist on a dump truck, feeds the wet kit on a tractor pulling a walking-floor trailer, drives the blower on a vacuum truck, turns a mixer drum, runs the winch on a wrecker and the crane on a service truck. Without a PTO, each of those bodies would need its own engine. In the UK, Ireland and Australia the same unit is called a lorry PTO.
How does a PTO work?
Every heavy-duty transmission has a PTO aperture, an opening on the side or bottom covered by a plate from the factory. Behind it is a gear that turns whenever the engine turns: the countershaft gear on a manual transmission, or a converter-driven gear on an automatic. The PTO bolts over the opening and its input gear meshes with that gear. When the driver engages the PTO, an internal gear or clutch connects the input to the output shaft, which turns a hydraulic pump bolted directly to the PTO or a driveshaft to a pump mounted further back on the frame.
Two numbers matter. PTO output speed is a fixed percentage of engine speed, set by the PTO’s internal ratio, so the pump has to be sized for it. Direction of rotation depends on which side of the transmission the PTO mounts, so the pump has to match that too.
What are the types of PTO?
By mounting. Six-bolt PTOs cover light and medium duty on most manual transmissions (Chelsea 442 Series, Muncie TG6 Series). Eight-bolt PTOs carry the heavy-duty work on Eaton Fuller, Mack and Tremec manuals and automated manuals (Chelsea 489 Series, Bezares 2000 Series). Ten-bolt PTOs fit Allison 3000 and 4000 automatics (Chelsea 281 and 871, Muncie CS10 and CS11). A split-shaft PTO mounts in the driveline behind the transmission and can take the engine’s full output for the biggest pumps and blowers (Fabco split-shaft PTOs).
By shift type. A mechanical PTO is engaged with a cable or lever, clutch pedal down. An air-shift PTO uses an air cylinder and a dash switch. A hot-shift PTO has an internal wet clutch that engages with the engine running, which is what an automatic needs and what any job that engages under load needs. A constant-mesh PTO is always engaged, so the pump turns whenever the engine does.
By output. A direct-mount flange (SAE A, B or BB) takes the pump straight on the PTO; a keyed shaft and yoke drive a remote pump.
PTO vs. wet kit: what is the difference?
The PTO is the gearbox on the transmission. The wet kit, or wetline kit, is the hydraulic system it drives: pump, oil tank, hoses, control valve and the air or electric control that plumb the PTO’s power back to a dump trailer. You need both. Wet kits for semi trucks are listed separately.
How to choose the right PTO
- Start with the transmission. The exact model (Eaton Fuller RT, Endurant, Allison 3000, Ford 10R140) sets the aperture, the bolt pattern and which side the PTO can mount.
- Know what it will drive. The pump’s displacement and pressure set the torque and horsepower the PTO must deliver, continuous if the pump runs all day.
- Match speed and rotation. Pick the ratio that puts the pump at its rated speed at your working engine RPM, and confirm the rotation the pump needs.
- Pick the shift type. Mechanical if you engage with the truck stopped; hot shift for an automatic or anything engaged under load; constant mesh if the pump never stops.
- Check clearance. A direct-mount pump saves a driveshaft but needs room next to the transmission, so look at the exhaust, crossmembers and air tanks first.
- Order by the full model number. The letters after the series set the gear, ratio, shifter and output, so two PTOs from the same series are rarely interchangeable. Read the tag.
Not sure? Call 877-776-4600 with the transmission model and what it will run, and we will spec the whole kit.
PTO parts manuals and diagrams
Common PTO problems and the repair kits that fix them are covered on the PTO parts hub. Our interactive parts manuals show every part in the exploded view with a price and an add-to-cart button: Chelsea 489 Series, Chelsea 442 Series, Chelsea 280 Series, Muncie TG Series and the Bezares PTO application catalog. The full set is under PTO manuals.