Transmissions commonly found in class 4 and larger vehicles may have provisions for the mounting of a Power Take-Off (PTO). Many popular transmissions have a PTO aperture on the side or bottom (such as an Eaton Fuller), while others may have top aperture opening (an example being an Allison RDS transmission). Many new transmissions also include provisions for Rear Mount PTOs. When PTO apertures are unavailable on the truck, or the torque requirement is too great for the transmission aperture, a builder may choose to utilize a split shaft PTO. A Split Shaft PTO is mounted independently of the transmission directly in-line with the vehicle’s main driveline. Identifying which solution to use is generally dependent on the available space around the PTO aperture, along with the PTO envelope space.
Six basic types of PTO mounting locations
The Side/Bottom Mount PTO is attached to the side or bottom of the transmission. This is the most common PTO in use and may be available for mounting via either an SAE standard six-bolt, eight-bolt or ten-bolt opening. When referring to left-side or right-side mounting, always view the transmission from the driver’s seat, rather than from the front of the vehicle. Because of its versatility, ease of installation, and low cost, the side-mount PTO comprises more than 90 percent of installations today. A popular example would be a Parker Chelsea's 280 Series PTO mounted to the side of an Allison 3000/4000 automatic transmission.
The Split Shaft PTO is designed to transmit a truck’s engine power and torque through the main driveshaft. The split shaft unit is used when space or power required is not available through standard PTO openings. It is attached within the vehicle’s drivetrain, behind the transmission, and requires special mounting to the chassis frame. Split shaft PTOs provide engine power to either the vehicle’s drive axle or to auxiliary equipment. This type of PTO, an example being the 912 Series Split Shaft PTO is designed to run either the vehicle axle or the auxiliary equipment, not both at the same time. Split shaft PTOs are often used to power oil drilling rigs, concrete pumpers, compressors, pumps, and lifts.
Top mount PTOs are designed to operate from and are attached to, the top (above the fluid line) of the Transmission or auxiliary transmission. They are used in heavy-duty applications, like Allison RDS. Similar to a side/bottom mount PTO, the major difference in top-mount applications is that press lubrication (supplying clean transmission fluid) is required in order to withstand applications. Noise is a common complaint about Top mounts. Parker Chelsea QT Gear is an ideal solution to help mitigate the noise from the PTO being mounted close to the truck’s cab.
Rear-mounted PTOs are frequently referred to as “countershaft PTOs” or “thru shaft." Rear mount PTOs are mounted behind certain transmissions and replace the normal bearing cap at the rear of the countershaft. This concept has long been used on some European truck transmissions and is becoming more popular on transmissions in North America. This type of PTO, such as the 524 Series, is mounted to a splined countershaft extension on the rear of certain transmissions and engages using an air-actuated clutch collar or clutch pack. One benefit of the Countershaft PTO is that there is no need to adjust backlash. Additional benefits include a higher than average torque, easier fit, fewer interference problems and reduced installation time. These PTOs are also available with SAE & DIN pump outputs, and SAE & DIN flange options.
Front Mount or Crankshaft – Driven PTOs are driven by the engine’s crankshaft pulley. They are used in heavy-duty and extra-heavy-duty applications that require auxiliary power while the vehicle is in motion, also known as Live Drive. These PTOs such as the 2442 Series can offer the ability to provide a large amount of clearance under a truck. A clutch-type Crankshaft-Driven PTO is preferable since it can be engaged without shutting off the engine, unlike mechanical shift PTOs. These are primarily used on dump trucks outfitted to plow snow. The PTO drives the hydraulics, which raises, lower, and swings the plow blade (or blades, if a wing plow and/or underbelly scraper are also used). Because the PTO can be entirely disengaged, it’s dormant in warmer months when the truck performs hauling and utility duties.
Flywheel PTOs are “sandwiched” between the bell housing and the transmission allowing full engine torque for intermittent operation. Since it supplies constant power, it can be an alternative to the front-mount PTO, especially if the vehicle’s overall length is an issue. But the flywheel PTO is about 6 inches in length, and the cost of moving the drivetrain back to accommodate it can be considerable. Flywheel PTOs reduce fuel consumption and CO2 emissions by engaging drives and pumps only when required, however, this type of PTO must be “designed in” by engine and transmission manufacturers and are seldom if ever, retrofitted in the field.
To learn more about the PTOs offered that apply to each of these mounting locations and other related content with PTOs, visit our website www.parker.com/chelsea.
This article was contributed by Michael Mabrouk, marketing leadership associate, Chelsea Products Division, Parker Hannifin Corporation.