Ask the Mechanic

Driveline Protection

(Steve Thompson)

READER: I have a question about driveline protection using a slip clutch, shear pin or both. My small rectangular baler has a slip clutch at the end of the driveline and a shear pin in the flywheel, but my round baler only has a slip clutch. What is the maintenance on the slip clutch, and is it important to use the dealer-recommended shear pin in the flywheel on the square baler, or can I get them from a local hardware store?

STEVE: The driveline on your rectangular baler is protected by the slip clutch. It is good at absorbing slower shock loads, like what happens during normal baling. It should slip before the driveline is damaged.

The clutch plates can rust against the pressure plates over time, especially if the baler is stored outside. If this happens, it will become locked together and will not slip. The best practice is to loosen the springs on the slip clutch during the winter, and after making sure they are not stuck, tighten the springs back to where they were when you loosened them before baling (see photo above).

The shear pin is there to protect the baler itself. It's designed to shear under hard shock loads, such as if a rock or chunk of wood gets caught between the plunger knives, an excessive charge of hay enters the bale case, and the plunger crank making contact with the baler's safety latch. This latch protects the needles if they end up in the bale case at the wrong time.

I highly recommend using shear pins supplied by the manufacturer. They will be of the proper hardness (or softness in some applications) to withstand hard or soft shock loads needed to run the machine but protect the machine when it's overloaded in a protected area.


-- Write Steve Thompson at Ask The Mechanic, 2204 Lakeshore Dr., Suite 415, Birmingham, AL 35209, or email, and be sure to include your phone number.