A power takeoff (PTO) is an attachment for connecting the engine to power-driven auxiliary equipment. It is attached to the transmission, auxiliary transmission, or transfer case. A power takeoff installed at the left side of a transmission is shown in Figure 10-25. It is used to drive a winch at the front of a truck through a universal joint and drive shaft.
Figure 10-25— Power takeoff and winch installation.
The simplest type of power takeoff is the single-speed, single-gear shown in Figure 10-26. This unit may be bolted to an opening provided in the side of a transmission, as shown in Figure 10-27.
Figure 10-26— Single-speed, single-gear power takeoff.
Figure 10-27 — Single-speed, single-gear power takeoff installation.
Shims or spacers are often used to ensure proper contact is maintained between the teeth of the two meshing units. The sliding gear of the PTO can then mesh with, and be driven by, the countershaft gear of the transmission or the auxiliary transmission when engaged by the operator. The operator, by the use of a control lever, can move the gear in and out of mesh with the transmission gear. A spring-loaded ball (poppet) holds the shifter shaft in position.
On some vehicles you will find PTOs with gear arrangements that give you two speeds forward and one in reverse. Several forward speeds and a reverse gear are usually provided in a PTO unit used to operate a winch or hoist. Operation of this type of PTO is similar to that of the single-speed unit.
Faulty operation of a PTO is caused by damaged or broken linkage. To prevent this, exercise care when shifting. Trying to engage the unit with the transmission gears turning can damage the teeth, and rapid clutch engagement can break the housing. Rapid shifting may bend or damage the linkage. Forcing the control lever can bend or break the linkage.
Adjustment of the linkage to compensate for wear and lubrication is normally all the maintenance required for the PTO unit. The gears and bearings are lubricated from the transmission sump.
If the PTO is to be removed for repairs, disconnect the drive shaft and shift linkage and drain the transmission. Once the transmission is completely drained, remove the bolts that secure the unit to the transmission. Do NOT misplace or lose any shims or spacers that are between the two housings. Once the unit is removed from the vehicle, the inspection and repair procedures are the same as for a transmission. When reinstalling or replacing the PTO, carefully follow the manufacturer’s procedures on the installation shims or spacers to prevent damage or unit failure.
5. What component is used to connect the engine to a power-driven auxiliary device?
In this chapter, you were introduced to the function of the power train. You learned how the power made by the engine is transmitted to the wheels through the transmission and transfer case. It is important to know how this power is distributed through the differentials and axles. You also learned how a vehicle can make a turn without the tires skidding around through the turn. In addition you learned about the problems associated with these systems, as well as how to troubleshoot them and make repairs. Mastering the knowledge of these systems will enable you to be a better auto and light truck technician.