All the powered implements for my tractor get their power from the tractor via the tractor power- take-off (PTO) and then through the driveline. Often overlooked maintenance-wise, PTO drivelines are relatively expensive items yet one of the most abused and ignored key pieces to the operation of farm equipment. Transferring all the power from the tractor to the driven implement takes some robust components that are exposed to everything.
Types
I have three different types of PTO in operation: a non shear, shear pin and slip clutch — the last being the most expensive.
Implement end of non shear (r) and shear type (l)
Non shear: this is a solid yoke to yoke set up and used with the expectation that certain equipment will not encounter any sudden stops. I figure that the finishing mower does not need a shear set up as the blades will slip to a degree being belt driven and my other mower, the flail mower, is extremely forgiving in its design.
Close up of shear pin which will shear in half if the implement is subject to sufficient resistance
Shear pin: the shear pin shaft I use for the chipper/shredder. The driven end yoke is actually two pieces with a shear pin or bolt that holds the two pieces as one during operation. Should the equipment encounter a sudden stop the pin will take the shock and “shear off” preventing any driveline damage.
Slip clutch: this type uses a slip clutch on the driven end yoke which is comprised of three steel plates in line held together with a series of bolts with springs under the nuts. The idea here is that when you tighten the nuts the pressure is increased onto the centre plate which when set up for the load will allow the shaft to turn and the implement to stall, absorbing the shock load. As mine is rated from 20-40 hp and I’m running a 17 hp I had to make alterations to set it up. Through trial and error I determined that I had to remove half the tension bolts and springs and back off the remainder nuts to minimum in order for the clutch to “slip” prior to stall on the tractor.
Slip clutch type on the rotary tiller, again slight oozing of grease on the UJ, do not grease the clutch; these run dry and should be “slipped” at least once a year to prevent rusting together
Coming from a line of farmers I’ve often discussed how stones will elevate from the bowels of the earth to rear their ugly head for the next time you want to plow or in my case rototill. If it wasn’t for the slip clutch I would have replaced the gear box on the rototiller or the PTO gears in the tractor a few times by now.
The actual driveshaft (components listed in order):
Close up of two yokes with the universal joint. Note the slight oozing of grease from the UJ seal ends, the clump of grease is from inside the yoke splined shaft area
--Drive (outer) yoke has a female (usual spline) hole and “Y” shape end that is the universal joint (UJ) mount.
--UJ is a cross shaped casting having roller bearings enclosed with caps at all four points and is held into the yoke with four “C” clips
--Inner yoke and drive shaft is another yoke welded to the drive end, of the drive shaft.
--Driven shaft and inner yoke is the driven shaft that rides inside of the drive shaft and has a yoke welded at the driven end
--UJ another UJ as above
--Driven (outer) yoke same as drive yoke but is mounted on the implement.
There are two types of shafts, domestic and metric, which are identifiable by their shapes. Domestic are generally one of four shapes: round, square, rectangle or splined. Metric are: bell, star or football shaped. In either case the primary (front) shaft is the same shape as the secondary shaft, only bigger so that the secondary shaft fits inside. This allows a telescoping effect to take place when the implement is raised on the 3 pt. or during a turning movement such as a bailer.
All shafts have to be sized before use. Attach the implement to the 3 pt. and raise and support it. Attach the proper end to the tractor and attempt to attach the other to the implement. If the shaft is too long trim one of the shafts with a hack saw and try it again until it fits. This allows for the implement to be raised without binding. The shafts should overlap as much as allowed.
Maintenance
Maintenance on these units is straight forward and like all moving parts these need their fair share of grease and should be greased regularly as these components work very hard and are subject to all that nature can provide for wear and tear. Good grease is essential here; put grease in until you see the old grease oozing out. Go easy on the “U” joints so you don’t blow the seals. Short bursts of a low pressured air grease gun or even better a hand pump gun will do the job and should be done based on hourly use. At least once a season the primary and secondary shafts should be separated. All debris and any rust should be cleaned off. Examine thoroughly for any signs of stress and apply a liberal amount of grease. In addition to this, both the PTO yoke holes need grease inside of them at least once a year along with the yoke lock pin.
PTO shaft pulled apart shows same design; left is larger (tractor end) right is smaller so it fits inside (implement end)
If you leave your equipment in the field you may want to remove the PTO shaft. They are too easy to steal and don’t come cheap, and as always, all PTO shafts should have guards in place.
- Dan Kerr