A Simple Upgrade For Tractor Attachments

The main purpose of a PTO slip clutch and shear bolt is safety. This provides an additional line of safety with PTO driven machinery on your tractor. A purposeful break in the power line when an implement is obstructed while in use. Common incidences include hitting stumps/foreign objects when topping or unexpected large rocks/lumps of concrete when rotovating.

Even the most robust of tractors or machinery will give when your attachment suddenly stops whilst running at 540 RPM or upwards. This may be within the tractor, the implement gearbox or even a failure in the PTO drive shaft all of which are costly and potentially dangerous outcomes.

Having either a PTO slip clutch or shear bolt aims to prevent any additional damage after the incident. Of course, there will be implications when a mower hits an immovable object in the field your best outcome is going to be broken blade and worst blades, blade carrier, damage to the deck etc.  But the PTO protection prevents further damage moving up the line, specifically at the tractor end of the line.


What Is A PTO Slip Clutch?

The PTO slip clutch uses a basic spring and disc set up. When it is overcome with too much torque the transfer of drive from the tractor to the machine is then limited. As the name suggests this starts slipping or free-wheeling so the two ends of the shaft can spin independently at different speeds.

The clutch is two plates compressed by the casing springs to transfer power to the machinery. Any obstruction causes the clutch to slip stopping the shock load from damaging the tractor or being contained in the attachment and causing further damage.

You should check the adjustment on the PTO slip clutch to make sure the springs are not set up too tightly and this causes it to not slip. It is also good practise to loosen off the springs occasionally to allow the clutch to slip. Otherwise the plates may rust and seize up preventing the PTO slip clutch from working in circumstances where it is needed.

PTO slip clutches are most commonly used on rotary tilling attachments (rotovators or stone buriers), heavy working brush cutters and rotary mowers. They can also be used on hay tedders, balers, hole diggers etc.


What Is A PTO Shear Bolt?

A PTO shear bolt/pin is often used on machinery where there is little chance of the machine being obstructed. It is also a cheaper option to supply than the PTO slip clutch.

The bolt shears under a designated amount of torque. When you hit a rock when cutting the idea is the pin would break and the PTO will spin freely and not powering the machinery. After the bolt is sheared the tractor should be stopped, the obstruction cleared, and a new bolt put into place.


Choosing Between A PTO Slip Clutch And Shear Bolt

Both devices give the same outcome breaking the line of power, but carry this out in two slightly different ways. The PTO slip clutch is usually favoured for convenience, especially in areas where machinery may be likely to come across lots of obstacles. For example managing an unkept area of land or working in heavily littered or compacted soil types.

Replacing sheared bolts requires stopping work, getting off the tractor and swapping bolts out. You need to keep a good supply of shear bolts to hand when using your machinery. Whereas the PTO slip clutch allows for the drive to be stopped when needed and resume the torque when free of any obstructions. This avoids too much interference when working and removes the need to be changing pins several times a day.

Tillers favour PTO slip clutches as often find rocks, potentially cables or chains which may cause work to seize. The PTO will still turn just with a heavier load and the engine may strain. This usually allows you to notice the resistance as your tractor continues onwards but without the rotovating. Tractor drive remain solid and if no damage to the rotovator, you could continue working once around the obstacle.


Other Handy Tips and General Safety

  • Always ensure that your PTO shafts are greased up before each use. This prevents excess wear and extends the life of the drive shaft.
  • Regularly check the PTO shaft for any cracks or damage to the casing and guards. Always replace your PTO straight away if there are any signs of damage. PTO shafts are a dangerous piece of equipment when in an unsafe condition!
  • Be safe. Always ensure drive is dis-engaged and at a complete standstill before working on or around your PTO.
  • More information PTO safety can be found in this handy HSE leaflet.
  • Our rotovators & tillers can be easily upgraded to slip clutch PTO shafts.
  • Our topper mowers can be easily upgraded to shear bolt PTO shafts.