Mowing PTO drive shaft sheering pins

Birddog1650 · Jul 9, 2013

I have a John Deere 50 hp tractor and recently purchased a County Line (tractor supply brand) 5' rotary mower that sheered a couple of bolts where the rear U joint connects to the gear box shaft. I purchased a clutch for the shaft at gear box thinking that may help but it continues to sheer the bolt before the clutch at mower gear box. I was cutting grass which was not high and started the pto at low speed and gradually brought it up to 540 rpm. I never had that problem with the older Howze mower I had. Any thoughts?

bullbreaker · Jul 9, 2013

What type(make) and grade are bolts being sheered ? Are they from same batch ?
Do you still have old cutter around and did it have S-bolt init to try that one ? Just some thoughts.

Boone

idaho2 · Jul 9, 2013

"I have a John Deere 50 hp tractor and recently purchased a County Line (tractor supply brand) 5' rotary mower that sheered a couple of bolts where the rear U joint connects to the gear box shaft."

By chance did the retailer put 90wt in the gear box. Most often they arrive at the retailer minus oil. Have you checked it? Sounds like something is binding that is shearing your bolts. Could a leaking seal be the culprit from tall grass wrapping around the output shaft and damaged the seal.
Just a thought.

idaho2

LD1 · Jul 9, 2013

1. Mower is grossly undersized and light duty for a 50HP tractor
2. Is the clutch adjusted properly for the tractor/mower combination
3. Are you still using grade 2 shear bolts? When converting to a slip clutch (that is set properly) use a stronger bolt

GManBart · Jul 9, 2013

If the slip clutch is set properly, I'd put a grade 5 or 7 bolt in it.

RickB · Jul 9, 2013

A real rotary cutter will have a splined input shaft that won't rely on a bolt to transmit the torque from the clutch to the gearbox.
Buy a cheap, light duty cutter and add a slipclutch, you have a cheap light duty cutter with a slipclutch. Use a Grade 8 bolt to attach the clutch to the gearbox and hope you can get along with it.