The Dangers of Using the Wrong Shear Bolts and How to Replace a Friction Clutch Disc
What happened to my driveshaft?!
If your customer brings you a twisted driveshaft they might not have any idea what caused the problem, but a good starting point to figuring out how to fix it is to ask them which grade shear bolts were being used on the shear bolt yoke.
A common error is replacing the shear bolts on the yoke with a harder grade bolt in an attempt to prevent the frequency of breakage. But if your customer’s shear bolts are breaking on their mower, for example, it might be due to mowing in conditions that the mower is not recommended for, such as places where you are hitting mounds of dirt and where the landscape is uneven. If the bolts are replaced with a harder grade, the next time the mower hits a mound of dirt, not only could the bolts break, but the blades might stop rotating and put undo torque on the gearbox. Now your customer will find himself with a twisted driveshaft or busted gearbox instead.
PRO TIP: Shear bolts need to be grade 2. To prevent bolt breakage strongly advise your customer to stop using his mower (or other implement) in conditions where it is not recommended!
Friction Clutch Discs
Friction clutch discs (pads) can be used in driveline clutches to provide overload protection, dissipate heat and balance torque. Finding a replacement clutch disc can be difficult unless you know the make or model of the mower, manufacturer of the shaft, size of the clutch or torque setting. This is information that most users don’t have readily on hand when they seek replacement parts. The easiest way to identify a clutch disc is to measure the disc being replaced. ID and OD do not change with the wear of the disc. If you can collect these two measurements, you can identify the disc needed from the following chart:
The following images demonstrate how to measure the OD and ID of a sample friction clutch disc (pad) and match those measurements to the correct part number in the identification chart.
The Friction Disc part number for the above example is highlighted in red on the identification chart below.
For more expert advice on PTO, drivelines, and parts replacement contact the RBH sales representative in your area.