Utilizing Split Shaft Power Take-Offs
Featured in Muncie Power Quarterly, Issue 2, 2016
Split shaft gearboxes have many advantages, which can make it an excellent option to capitalizing on the full potential of your work truck. While very beneficial, there are some considerations to keep in mind as well.
These gearboxes provide higher horsepower and torque capabilities than transmission mounted power take-offs (PTOs) running auxiliary components. When transmission PTO openings are obstructed, the split shaft gearboxes provide multiple outputs.
Available in various styles and sizes, some split shaft gearboxes have shiftable driveline or hydraulic pump mount outputs. Others have standard PTO openings that accept PTOs with various outputs, shift types, and output speeds.
While this may sound like the solution to capitalizing on the full potential of a work truck, you need to be aware that there are also obstacles to utilizing this potential. Rounding out the list of deterrents is cost, truck compatibility, installation issues, and operational issues.
Depending on the split shaft, the gearbox cost alone can greatly exceed that of a transmission mounted PTO. And any split shaft where PTOs can be mounted results in an added cost for the PTO. You must also consider installation cost. Not all truck modification shops can provide this type of specialized installation.
Compatibility with the truck and transmission is the most overlooked obstacle. Some chassis and transmission combinations are not set up to allow split shaft operation, resulting in fault codes, warning lights, or even drivability restriction.
Trucks with automatic transmissions need to have a way to be locked into the selected shift range during split shaft operation. If not, when the split shaft is under load, the transmission may shift into different gear ranges, changing the input speed to the split shaft. This can cause undesired performance and possible component damage.
Beyond compatibility, there are some installation issues that need to be considered as well.
Space: There needs to be enough room to mount the gearbox and the auxiliary equipment. Things like exhaust, air tanks and fuel tanks can be obstacles to placing the gearbox in the chassis.
Length of the chassis: Length is critical for space to mount the split shaft and auxiliary equipment and for the required changes to the length and setup of the driveline. Changes to the driveline can create serious vehicle drivability issues if not done correctly.
The parking brake: The parking brake needs to be set during stationary operation. If the truck is not big enough to have air brakes, the parking brake is accomplished by locking the rear drum brakes by cable. However, if the parking brake is a driveline drum brake, it will need to be moved from the tail of the transmission to the rear driveline behind the split shaft or provide some other method of locking the drive wheels.
Operation of the split shaft is usually done in a stationary position as the split shaft is shifted and the rear axle disengaged from the drivetrain. Shifting of the main shaft or an output into gear or out of gear requires that the input driveline to the split shaft be stopped before shifting.
Stopping the input for shifting is necessary and must be considered if multiple outputs are used during operation. The shifting procedures for split shaft operation are different depending on whether you have a manual or automatic transmission. Operators need to be thoroughly trained to prevent damage.
A split shaft, when installed, becomes part of the drivetrain of the truck. Just like any other drivetrain component, it will need regular maintenance checks, fluid changes, and, if something should go wrong, the truck will be out of commission until it is repaired.
If you are looking for a way to get more out of your truck than what a transmission PTO opening can provide, a split shaft gearbox could be the perfect solution. But before you dive in, be sure to do your homework first.
