shear pin breakage

Toby873 · May 31, 2006

Howse 6' cutter behind a Branson 4720. Broke my first shear pin due to starting the pto way too fast, second pin broke for unknown reason, now I have just sheared my third pin cutting grass, my pto is at proper speed, I am going at a good rate of speed, and I was CUTTING GRASS......I cant stand this. Any help?

Toby873 · May 31, 2006

Howse 6' cutter behind a Branson 4720. Broke my first shear pin due to starting the pto way too fast, second pin broke for unknown reason, now I have just sheared my third pin cutting grass, my pto is at proper speed, I am going at a good rate of speed, and I was CUTTING GRASS......I cant stand this. Any help?

BB_TX · May 31, 2006

Not familiar with the Branson 4720. I run a Howse 6' behind a JD 950 (27 PTO HP) with no problems. I shear maybe 3 bolts a year using standard grade 2 bolts mowing pasture and occasional brush.

BB_TX · May 31, 2006

Not familiar with the Branson 4720. I run a Howse 6' behind a JD 950 (27 PTO HP) with no problems. I shear maybe 3 bolts a year using standard grade 2 bolts mowing pasture and occasional brush.

InlineDieselFan · May 31, 2006

Unless you are hitting something be it the ground, rocks, wood. This would not seem normal, are you using the proper size shear pin? I do not know Branson tractors but I asssume a 4720 is 47 HP? That would not seem to be way over powered for a 6 foot brush hog.

What rating of bolt is it?

Are the blades able to move freely, so that when you hit the thick patch of grass the blade can move.

Those would be my guesses.

steve

InlineDieselFan · May 31, 2006

Unless you are hitting something be it the ground, rocks, wood. This would not seem normal, are you using the proper size shear pin? I do not know Branson tractors but I asssume a 4720 is 47 HP? That would not seem to be way over powered for a 6 foot brush hog.

What rating of bolt is it?

Are the blades able to move freely, so that when you hit the thick patch of grass the blade can move.

Those would be my guesses.

steve

KiotiJohn · May 31, 2006

I've seen ratings for shear pins from grade 2 to grade 5 bolts. 5 seems high, but some manufacturers use them in their equipment. I would suggest, since this is happening in only grass, that your mower requires a higher grade shear pin. If you're using a 2 trying going to a 5 and see if that fixes it.

Of course, you should check the mower's manual first to see what they recommend. My Howse mower uses a grade 5.

John

KiotiJohn · May 31, 2006

I've seen ratings for shear pins from grade 2 to grade 5 bolts. 5 seems high, but some manufacturers use them in their equipment. I would suggest, since this is happening in only grass, that your mower requires a higher grade shear pin. If you're using a 2 trying going to a 5 and see if that fixes it.

Of course, you should check the mower's manual first to see what they recommend. My Howse mower uses a grade 5.

John

MrSteve · May 31, 2006

I would go with your blades are not swinging out like they should... Take a look under the cutter and see if they are "out" before hitting the PTO and if the pin breaks again, before you do anything look under the mower and see where the blades are AFTER the break.

Maybe you have your RPMs to hight when turning the PTO on?

When I got my tractor and mower the dealer right there on the lot broke a pin showing me how to turn on the PTO. Well he set the RPMs to 1100 or so when that happen. So what I have done, is turn on the PTO at idle speed and I have never broken a pin.

MrSteve · May 31, 2006

I would go with your blades are not swinging out like they should... Take a look under the cutter and see if they are "out" before hitting the PTO and if the pin breaks again, before you do anything look under the mower and see where the blades are AFTER the break.

Maybe you have your RPMs to hight when turning the PTO on?

When I got my tractor and mower the dealer right there on the lot broke a pin showing me how to turn on the PTO. Well he set the RPMs to 1100 or so when that happen. So what I have done, is turn on the PTO at idle speed and I have never broken a pin.

greg_g · May 31, 2006

Toby - the 4720 has two PTO speeds; 540 rpm and 1000 rpm.
Are you positive you're mowing at the 540 rpm setting? Because spinning those heavy blades at 1000 rpm PTO speeds can be real hard on a 1/2 shear pin - even if you DON'T hit anything

//greg//

greg_g · May 31, 2006

Toby - the 4720 has two PTO speeds; 540 rpm and 1000 rpm.
Are you positive you're mowing at the 540 rpm setting? Because spinning those heavy blades at 1000 rpm PTO speeds can be real hard on a 1/2 shear pin - even if you DON'T hit anything

//greg//

Highbeam · May 31, 2006

I have never broken a shear pin on this mower. Check out the photo. The yellow slip clutch is pretty cheap at agrisupply.

Highbeam · May 31, 2006

I have never broken a shear pin on this mower. Check out the photo. The yellow slip clutch is pretty cheap at agrisupply.

BB_TX · Jun 1, 2006

Neat idea on the rear wheel, Joe. Never thought about swinging it up like that for trailering. /forums/images/graemlins/smile.gif

BB_TX · Jun 1, 2006

Neat idea on the rear wheel, Joe. Never thought about swinging it up like that for trailering. /forums/images/graemlins/smile.gif

Toby873 · Jun 1, 2006

Snapped another one after hammering the last one out. Mowing a previously mowed field. PTO is right speed, not hitting anything. Slip clutch? Does it still require a shear bolt?
Toby

Toby873 · Jun 1, 2006

Snapped another one after hammering the last one out. Mowing a previously mowed field. PTO is right speed, not hitting anything. Slip clutch? Does it still require a shear bolt?
Toby

Highbeam · Jun 1, 2006

Swinging that wheel up saves me from a big overhang and the potential legal hassles with that. I trailer a lot of miles and like having that wheel swung up. The tailwheel doesn't pivot around either, it just sits there.

The slip clutch is held on by the former shear pin. You use a strong bolt though so that it won't shear. I ordered my RC with it so I didn't have to do the install but the PTO shaft might need to be shortened a little.

This doesn't explain why the poster's shear bolts are shearing so easily though.

Highbeam · Jun 1, 2006

Swinging that wheel up saves me from a big overhang and the potential legal hassles with that. I trailer a lot of miles and like having that wheel swung up. The tailwheel doesn't pivot around either, it just sits there.

The slip clutch is held on by the former shear pin. You use a strong bolt though so that it won't shear. I ordered my RC with it so I didn't have to do the install but the PTO shaft might need to be shortened a little.

This doesn't explain why the poster's shear bolts are shearing so easily though.