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2 mower deck strikes - clipped a rock and chipped a tooth


 
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Dan Newell
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Location: Spokane, WA

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PostPosted: Thu Sep 13, 2018 8:04 pm    Post subject: 2 mower deck strikes - clipped a rock and chipped a tooth Reply to specific post Reply with quote

I have a 6-speed '69 MF-135 with independent PTO and single split clutch. While brush-hogging with a 72" mower deck I clipped a rock and broke a tooth from the PTO constant mesh gear. That was several years ago. After replacing said gear I was good to go for a few more years until darn it, I did the exact same thing. The 1/2" grade 2 shear bolt failed but not before the gear tooth became a casualty also. Has anyone else had this experience? Before I proceed with replacing the gear and once again attempting to steer clear of hard objects, is there anything else to consider?
 
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John Deere D
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PostPosted: Fri Sep 14, 2018 5:33 am    Post subject: Re: 2 mower deck strikes - clipped a rock and chipped a toot Reply to specific post Reply with quote

Good morning..........
Do you know if a 1/2" shear bolt is the correct size...as per original Shear bolt size?

Reason I ask ...my Father once owned a PTO driven piece of equipment that was suffering from Previous Owner Syndrome.

Someone had drilled the Shear bolt hole oversize... replaced with an over size bolt.


Bob..
 
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Dan Newell
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PostPosted: Fri Sep 14, 2018 8:06 am    Post subject: Re: 2 mower deck strikes - clipped a rock and chipped a toot Reply to specific post Reply with quote

Good point and question. The mower is "previously owned" and the only thing I can say for sure is that I didn't change it. Knowing just a little about the previous owner, he didn't strike me as the type who would knowingly stretch the limits and put undo stress on the tractor. Also I've come across other discussions where 1/2" diameter was identified as the shear bolt size.
 
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Caryc
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PostPosted: Fri Sep 14, 2018 8:31 am    Post subject: Re: 2 mower deck strikes - clipped a rock and chipped a toot Reply to specific post Reply with quote

Dan Newell wrote:
(quoted from post at 21:04:06 09/13/1Cool I have a 6-speed '69 MF-135 with independent PTO and single split clutch. While brush-hogging with a 72" mower deck I clipped a rock and broke a tooth from the PTO constant mesh gear. That was several years ago. After replacing said gear I was good to go for a few more years until darn it, I did the exact same thing. The 1/2" grade 2 shear bolt failed but not before the gear tooth became a casualty also. Has anyone else had this experience? Before I proceed with replacing the gear and once again attempting to steer clear of hard objects, is there anything else to consider?


You might think about installing a slip clutch on that mower shaft. I have a stump jumper and a slip clutch on my Woods M5 mower and have never had any problems. A slip clutch can be set to slip with any amount of resistance that you want and you never have to replace any shear bolts. It takes a heck of a whack on the mower to break a shear bolt.

Tractor Supply sells slip clutches.


 
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David G
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PostPosted: Fri Sep 14, 2018 7:34 pm    Post subject: Re: 2 mower deck strikes - clipped a rock and chipped a toot Reply to specific post Reply with quote

I would agree on the clutch, will prevent teeth and shear bolt damage.
 
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Caryc
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PostPosted: Fri Sep 14, 2018 9:14 pm    Post subject: Re: 2 mower deck strikes - clipped a rock and chipped a toot Reply to specific post Reply with quote

The "slippage" or tension on the clutch can be adjusted simply by tightening or loosening the nuts on the springs. You can take a felt tip black marker and make a mark on the middle plate and the outer plates on the clutch to see if it is indeed slipping. If the marks are no longer lined up after mowing then you know the clutch is slipping.

I guess if you loosen it until is is slipping too much, you will know by the ragged cut produced by the mower. I really much prefer a slip clutch over the shear bolt thing. When that bolt does break, your PTO has taken quite a hit as you've already experienced
 
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wellmax99
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PostPosted: Sat Sep 15, 2018 7:45 pm    Post subject: Re: 2 mower deck strikes - clipped a rock and chipped a toot Reply to specific post Reply with quote

Does your cutter have a stump jumper with blades attached or just a bar with blades attached

Is the pto shaft loose (not rusty or frozen to the shaft) on the gearbox, so that if you hit something the bolt could sheer and turn on the gearbox
shaft,

I would also double check to be sure you have grade #2 soft sheer bolts, on my old 5 ft cutter and TO35 Ferguson I sheer bolts by just being in
heavy weeds and grass, I had to bump up to grade #5 bolts to kept them in so I could keep working,
Maybe you got some bolts mix marked, I would buy some new grade #2 bolts from a different supplier have them check the marks on the bolt
 
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Caryc
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PostPosted: Sun Sep 16, 2018 9:05 am    Post subject: Re: 2 mower deck strikes - clipped a rock and chipped a toot Reply to specific post Reply with quote

CVPost-wellmax99 wrote:
(quoted from post at 20:45:09 09/15/1Cool Does your cutter have a stump jumper with blades attached or just a bar with blades attached

Is the pto shaft loose (not rusty or frozen to the shaft) on the gearbox, so that if you hit something the bolt could sheer and turn on the gearbox
shaft,

I would also double check to be sure you have grade #2 soft sheer bolts, on my old 5 ft cutter and TO35 Ferguson I sheer bolts by just being in
heavy weeds and grass, I had to bump up to grade #5 bolts to kept them in so I could keep working,
Maybe you got some bolts mix marked, I would buy some new grade #2 bolts from a different supplier have them check the marks on the bolt


Even if his mower just has a bar with the blades attached he should still install a stump jumper on it. That blade bar smacking into a rock will put a heck of a jolt on his mower shaft. The stump jumper with it's curved lip on the edge will ride up over the rock.

Below is the stump jumper I got to fit on the blade bar on my Woods M5 mower. You can see how it attaches to the blade bar. The two outer holes are where the big blade pins go in. It's a very heavy and strongly built piece.


 
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MF-Dan
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PostPosted: Sun Sep 16, 2018 1:39 pm    Post subject: Re: 2 mower deck strikes - clipped a rock and chipped a toot Reply to specific post Reply with quote

The deck has a stump jumper in place. (I've added a picture.) I think the ticket just might be going with a slip clutch. Is the one you have the "Weasler Universal Friction Clutch, 1 3/8 in.; 6-spline both ends?"

 
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Caryc
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PostPosted: Sun Sep 16, 2018 2:09 pm    Post subject: Re: 2 mower deck strikes - clipped a rock and chipped a toot Reply to specific post Reply with quote


Actually my slip clutch was built integral with the mower at the factory. It bolts onto the round keyed shaft on the gear box and as you can see, it has a "U" joint on the piece that goes between the clutch plates. That piece has a square shaft on it that the round shaft slips over.

The one that I pictured above is an aftermarket unit. You can usually buy the to fit the kind of shaft you are running on your mower.

Below is a picture of mine when I was replacing the clutch discs in it.

You can see how a slip clutch works. That middle round plate is on the end of the square drive shaft. The two big outer plates have a clutch disc that rides against either side of the plate with the shaft. The long bolts and springs clamp the two outer metal plates against the discs and the middle plate.

The springs regulate how much pressure the discs put against the middle plate that drives the mower shaft



 
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MF-Dan
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PostPosted: Sun Sep 16, 2018 2:41 pm    Post subject: Re: 2 mower deck strikes - clipped a rock and chipped a toot Reply to specific post Reply with quote

Very fine Caryc. Your response and input are much appreciated. I believe that the aftermarket option just might provide the 'upstream' protection I need to keep from breaking something internal and having to go through the expense and ordeal of repairing it, again.

My best regards,
Dan N
 
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