There's a huge amount of attachments that have shear pin protection. If this method was so bad, we'd not see them around. Are people overstating how bad this form of protection is? I'd wager that lots of people have poorly maintained slip clutches and they get by amply.
Shear pins and their woes or lack thereof
- Thread starter msjanket
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Poopdeck Pappy
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Shear pins are just fine for mowing established pasture and areas where "surprises" are not very likely. But mowing brush and/or tall grass areas where all manner of unknown surprises may lurk, even things as simple and common as fire ant mounds, you'd better have an ample supply of shear pins on hand.
Slip clutches are simply a better solution. More expensive to buy, but less trouble in the long term.
Slip clutches are simply a better solution. More expensive to buy, but less trouble in the long term.
What do you mean poorly maintained? I looked at mine when I bought it 19 years ago. What more would want?
CADplans
Elite Member
This mower has a shear pin,,,
It had a grade 5 3/8" bolt in the pto when I bought it.
After a year, the pto shaft blew apart, the outer sliding tube exploded like a watermelon.
I did not hit anything, and was mowing normal grass.
I got a new complete pto off of eBay, and switched to a grade 2 bolt.
twice in less than a season of mowing the bolt has sheared.
The tractor does not have a "live" pto, so, letting the clutch out engages the pto.
Well,,, I found letting the clutch out too fast will shear the bolt.
I truly need a grade 3.5 bolt!! LOL!! :confused2:
It had a grade 5 3/8" bolt in the pto when I bought it.
After a year, the pto shaft blew apart, the outer sliding tube exploded like a watermelon.
I did not hit anything, and was mowing normal grass.
I got a new complete pto off of eBay, and switched to a grade 2 bolt.
twice in less than a season of mowing the bolt has sheared.
The tractor does not have a "live" pto, so, letting the clutch out engages the pto.
Well,,, I found letting the clutch out too fast will shear the bolt.
I truly need a grade 3.5 bolt!! LOL!! :confused2:
Stubee
Silver Member
I actually thought my B2320 had a slip clutch until the shear bolt nut worked loose. Was darned lucky my friend walking behind me heard it drop onto the 4' bush hog as I was easing over a boulder-strewn muck hole or I woulda lost it when I started the hog again.
I run that bush hog only in thick grass (3' high+) and weeds up in NW ONT and also go over any sapling big enough to bend with the tractor. I've also inadvertently & alarmingly stopped the whole darned tractor when a big chunk of log dragged into a thick area by a bear got pulled up into the hog, or I stupidly spun the thing into a hidden stump or rock (!) cutting a new trail. I cut about two miles of miserable trail & shooting lanes in land my ATV shies away from and haven't broken the original bolt yet.
I do lube everything up, check that bolt and was even able to not hit a single rock last year for the first time in five seasons. But I'm now a believer in the utility of a shear bolt in a woods tractor.
I run that bush hog only in thick grass (3' high+) and weeds up in NW ONT and also go over any sapling big enough to bend with the tractor. I've also inadvertently & alarmingly stopped the whole darned tractor when a big chunk of log dragged into a thick area by a bear got pulled up into the hog, or I stupidly spun the thing into a hidden stump or rock (!) cutting a new trail. I cut about two miles of miserable trail & shooting lanes in land my ATV shies away from and haven't broken the original bolt yet.
I do lube everything up, check that bolt and was even able to not hit a single rock last year for the first time in five seasons. But I'm now a believer in the utility of a shear bolt in a woods tractor.
Fallon
Super Member
A slip clutch is actually a lot more work in many cases. You need to spend half an hour annually to clean & adjust them.
Generally loosen up the bolts. Start up the PTO so the clutch slips a bit, it will free up stuck disks & polish up rusty surfaces. Then you re-tighten up the bolts to spec.
If you don't do that, your clutch is probably rusted & locked up so it won't slip when it's supposed to.
A sheer pin never needs adjustment or maintenance. Just replace it when it breaks.
My dealer told me my rotary cutter had a clutch, not a pin. Was upset when I went to do my anuall maintnance on it & found a pin, not a clutch under the shields. still upset at the dealer, but realized if I'm not breaking sheer pins in a year (now 3) it's a lot less work to maintain.
Generally loosen up the bolts. Start up the PTO so the clutch slips a bit, it will free up stuck disks & polish up rusty surfaces. Then you re-tighten up the bolts to spec.
If you don't do that, your clutch is probably rusted & locked up so it won't slip when it's supposed to.
A sheer pin never needs adjustment or maintenance. Just replace it when it breaks.
My dealer told me my rotary cutter had a clutch, not a pin. Was upset when I went to do my anuall maintnance on it & found a pin, not a clutch under the shields. still upset at the dealer, but realized if I'm not breaking sheer pins in a year (now 3) it's a lot less work to maintain.
Poopdeck Pappy
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It takes about 15 minutes to do the maintenance on my slip clutch on my rotary cutter.
CalG
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This mower has a shear pin,,,
It had a grade 5 3/8" bolt in the pto when I bought it.
After a year, the pto shaft blew apart, the outer sliding tube exploded like a watermelon.
I did not hit anything, and was mowing normal grass.
I got a new complete pto off of eBay, and switched to a grade 2 bolt.
twice in less than a season of mowing the bolt has sheared.
The tractor does not have a "live" pto, so, letting the clutch out engages the pto.
Well,,, I found letting the clutch out too fast will shear the bolt.
I truly need a grade 3.5 bolt!! LOL!! :confused2:
A couple of "shear grooves" machined into a grade 5 bolt would do the trick. Five minutes for the first one by anyone with a tooled up lathe.
What do you mean poorly maintained? I looked at mine when I bought it 19 years ago. What more would want?
Poor maintenance of a slip clutch includes not keeping the disks slipping well. The fiber disks can literally fuse with the metal friction surfaces and then this happens, the slip clutch doesn't slip. I've bought attachments that had stuck fiber disks and had to either replace the disks, hone the friction surfaces, or both.
Some people say "shear pins are better than poorly maintained slip clutches". I hope my example sits OK with you. Fusing comes about when the fiber disks get moist and rust forms on the friction elements thereby sticking them together. This is not desirable. If this hasn't happened to your attachments, you are obviously doing something right. Congrats!
This mower has a shear pin,,,
It had a grade 5 3/8" bolt in the pto when I bought it.
After a year, the pto shaft blew apart, the outer sliding tube exploded like a watermelon.
I did not hit anything, and was mowing normal grass.
I got a new complete pto off of eBay, and switched to a grade 2 bolt.
twice in less than a season of mowing the bolt has sheared.
The tractor does not have a "live" pto, so, letting the clutch out engages the pto.
Well,,, I found letting the clutch out too fast will shear the bolt.
I truly need a grade 3.5 bolt!! LOL!! :confused2:
Seems to me that using a smaller diameter grade 5 bolt would prevent that initial inertial shearing action that busts the bolt. You'd have to drill a hole to accomodate the smaller diameter bolt, of course. Prior to that, you'd have to do some metallurgical mathematics and find the mechanical capabilities of the smaller, harder bolt. But, in principle, this is NOT a bad idea. If shearing of the grade 2 bolts due to that initial yank is busting too many bolts, having a factory supplied hole of smaller diameter using the harder grade 5 bolt is probably worth a shot. You'd have to compare the shear strengths of both bolts and that is obtainable from the Internet on Google. Let me know if you get bogged down in the analysis of the respective strengths of the 2 bolts differing in diameter.