Go BottomDo I need to add a slip clutch on a 4’ Howes bush mowers
 | Joe D.
Join Date: Posts: 1 
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2003-02-21 49720
I assume never have seen a slip clutch for a bush mower that it attaches to gear box PTO shaft and can help protect the tractor drive line.
I’m pulling mower behind an YM1500 Yanmar and going to help a friend clear a piece of land.
Thanks ahead of time.
Joe
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 | BillMullens
Join Date: Jun 2000 Posts: 649 Central West Virginia 
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2003-02-22 49801
There is some type of slip clutch that is meant to protect the tractor, driveline and mower BUT usually the smaller and cheaper rotary cutters (the only kind I've seen) have a shear bolt for protection. Exceed the rated power, or incur a shock load, and the bolt shears. Replace it and keep going.
You may be thinking of an "overrunning clutch" that is used on tractors that don't have a live PTO. It is a clutch mechanism that only transmits power one way; so if the rotary cutter's speed exceeds the PTO speed, the clutch slips to keep the implement from pushing the tractor. It fits onto the PTO shaft on the tractor; the implement driveshaft attaches to the overrunning clutch.
Bill ....
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| Joe D.
Join Date: Posts: 1
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2003-02-23 49848
Just purchased the overrunning clutch, but I had heard you could get a slip clutch for the other side of the shaft.
I do not know if it would replace my shear bolt or go on before or after it.
To tell the truth I’ve only seen picture of them on the Internet and when I asked the local tractor dealer I purchased my slip clutch from, he stated I mite be money ahead if I added a slip clutch to my bush mower.
He sold me my overrunning clutch for $44 and said he could get the slip clutch for about $100.
From what I can tell from the Internet the price overrunning cutch was more than fair.
Thanks again,
Joe
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| loghouse95
Join Date: Jul 2003 Posts: 87 missouri
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2003-05-02 54187
make sure you use the right grade shear bolt and I would not think there would be any need for a slip clutch ....
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 | plots1
Join Date: Jul 2003 Posts: 563 mo
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2003-05-02 54191
As loghouse stated , make sure your shear pin is the correct grade.!!! I have had my cutter stall earlier this year and got heavy clutch stink.after taking a good look at shear pin found it was a grade 5 instead of a grade 2.gear box on cutter was protected but hard on tractor clutch. it was the pin that came with my kk cutter, oops someone made a mistake. MAKE SURE TO CHECK BEFORE USING! having the wrong pin installed could result in big damage, lucky for me mine faired ok that time. slip clutch might be a good safety device. ....
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| MarkStewart
Join Date: Jul 2003 Posts: 1 Pine Bush, NY
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2003-05-14 54893
I just bought a howse 42" cutter. It also came with a grade 5 bolt as shear pin. I think I might have damaged my pto gears on my ym1401. It still works but I have to play with clutch for it to slip into gear. It doesnt make any weird noises so I hope it isn't terminal. I wish I would have known that it wasn't the right bolt when I bought it. You would think that with a 42" cutter they would have put a lower grade pin in it. ....
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 | Billy
Join Date: Oct 1999 Posts: 975 Southeast Oklahoma 
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2003-05-14 54894
You need to use a grade 5 shear bolt, not a grade 5 bolt. If you're going to use a plain bolt as a shear bolt use a grade 2.
The two implements I have that use a shear bolts both use a grade 8.8 metric (grade 5 SAE) shear bolt. ....
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 | Peters
Join Date: Feb 2002 Posts: 3034 Northern AL 
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2003-05-14 54900
Billy how do the marks differ for a grade 5 shear bolt and a regular SAE grade 5? ....
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| BillBass
Join Date: Feb 2002 Posts: 190 North Texas
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2003-05-15 54903
Joe-Tractors are protected from the implements by either a shear bolt or a slip clutch. Seems implements that are larger and/or require more power and/or a little more expensive tend toward the clutches. Here is a link to a basic description. ....
Link: Tractor FAQS
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| Billy
Join Date: Oct 1999 Posts: 975 Southeast Oklahoma
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2003-05-15 54906
Eric, the shear bolts that came with the implement has a ring cut around it. Other than that, the markings are the same.
I could be totally wrong about this whole shear bolt thing?
Billy ....
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| TomG
Join Date: Feb 2002 Posts: 5406 Upper Ottawa Valley
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2003-05-15 54907
Dang! I can't find my link to a site that had good drawings of bolt-head codings. I think I found it by searching of 'hardware specifications' or something like that. There could be a series specifically for shear bolts but I don't recall.
You can't assume that all shear bolts should be Grade-2. Hard bolts have been used is some applications. When I had a question about my PHA, my dealer called the manufacturer to verity the proper bolt for the auger. Many pto shafts have their own shear bolts and the bolt may or may not be appropriate when implements and pto shafts have been mixed and matched.
I've wondered why I've never heard of using both a clutch and a shear pin. Seems to me like it'd be a good idea since the clutch could be adjusted to protect the shear pin. Then there'd be less risk of loosing protection due to an improperly adjusted or seized clutch. Clutches may be better than pins for protecting against high loads rather than sharp shocks as well.
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 | Murf
Join Date: Dec 1999 Posts: 7249 Toronto Area, Ontario, Canada
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2003-05-15 54912
I think a lot of people confuse a shear pin (bolt) with an inexpensive type of driveshaft retainer system. The norm on standard duty driveshafts is the spring-loaded pin type, and on more expensive ones sometimes a twist-lock type of coupler. However on lower priced units it is common to find just a cross-drilled hole through which a 1/4" bolt is placed to keep the two splines together.
This bolt is not, and cannot function as, a shear bolt since it joins two SPLINED faces, not smooth shafts which could spin free were it not for the bolt.
A slip-clutch on the other hand is usually setup with a female spline on one end and a male spline on the other and it goes between the driveshaft and the gearbox, kind of like a small extension. It usually consists of three steel plates seperated by discs of friction material, like brake or clutch linings, with the 1st & 3rd steel plates connected to one spline, the middle one connected to the other spline. The entire 'sandwich' is then squeezed together by bolts through only the two outside plates, this locks the three steel plates, and therefore the two splines, together by the friction generated. Sometimes shortening of the driveshaft is required after adding the slip-clutch to maintain proper allowance for contraction of the shaft.
The trick is to get the bolts tight enough to keep the driveshaft turning the gearbox under normal loads, but loose enough that when an obstacle is hit, the clutch can spin free and release the load from the gearbox.
Best of luck. ....
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| Murf
Join Date: Dec 1999 Posts: 7249 Toronto Area, Ontario, Canada
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2003-05-15 54925
BTW, a bolt head with no hash marks at all is a Grade 2 bolt, 3 hash marks denotes a Grade 5 bolt, and 6 hash marks denotes a grade 8 bolt. ....
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| Peters
Join Date: Feb 2002 Posts: 3034 Northern AL
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2003-05-15 54928
Billy;
I grade 2 does not do that well as a shear bolt has it is too soft to snap in the right conditions. With a sharp blow you can have plastic bending of the bolt. From what you describe I guess they take a grade 5 and turn a ring in it to provide a break point.
Most of my experience has been with shear pins used in marine and industrial applications. I have never seen a bolt used as once the bolt breaks it can become a projectile. I believe shear pins are case hardened (they are harder at the surface than in the interior of the pin). This provides ha heard outer coating for wear that once cracked breaks easily. Sort of like a pretzel. Bolts are not case hardened as you have different thicknesses and do not really want the threads to be harder than the interior of the bolt.
I guess I am saying it would be better to use a shear pin, but the difficulty of replacement in the field prevents the application. ....
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| Billy
Join Date: Oct 1999 Posts: 975 Southeast Oklahoma
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2003-05-15 54929
Yep Murf and metric grades are marked with their number of grade stamped on the head. The metric way seems so much simpler. If it's an 8.8, it's stamped 8.8.
Murf, while I have your attention. Is there any difference in a 'shear' bolt and a fastener bolt?
Billy ....
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| Billy
Join Date: Oct 1999 Posts: 975 Southeast Oklahoma
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2003-05-15 54932
That makes sense Eric. I do believe a grade 2 bolt is too soft for a shear bolt.
I have heard of people using grade 2 bolts for shear pins but I've also heard them say they have to replace them way to often.
Billy
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| Murf
Join Date: Dec 1999 Posts: 7249 Toronto Area, Ontario, Canada
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2003-05-15 54935
Billy, the only difference I know of between a 'shear' bolt and a 'fastener' bolt is about $1.00 a piece....
Seriously, the only difference I have ever seen is the (very) odd case where the bolt had been stamped to form a weak spot in order to ensure that the bolt snapped cleanly at the correct spots so as not to create a burr in the shaft which would make it difficult to get apart by hand.
As Peters mentioned, Grade 5 bolts are the norm since they are more brittle and the tend to snap at exactly the point of maximum stress, the seam between the two parts. In most cases where the shaft is enclosed, like a boat engine, they use a smooth pin of the correct length not a bolt, however I think this is more to retain the peices, propeller included, than anything else. The shear bolts that came with my new snowblower were standard 1/4" Grade 5 bolts, cadmium plated even, though I'm not sure why, rusted threads on a shear bolt are of no concern to me when they fly off into the snowbank... go figure.
Best of luck. ....
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| TomG
Join Date: Feb 2002 Posts: 5406 Upper Ottawa Valley
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2003-05-16 54960
Never the less, the manufacture of my PHA speced a 5/16" grade-2 bolt, which is an ordinary hardware piece. It goes through a cross-hole in the auger shaft. My impression is that the use of grade-2 bolts is fairly common so it would be a good idea to verify what is required.
The pin for my snowblower is much smaller--6mm I think. Guessing from the diameter it is probably hardened. I have a supply of bolts but I guess I'd better verify what they are before next winter. A parts guy in a nearby dealership couldn't ID the bolt but said their 'bolts-guy' (a salesman) likely could figure it out. The pin for my snowblower goes through the flange of the pto shaft at the drive end.
I've heard of soft bolts bending rather than breaking but usually in cases where the bolts are very loose or the shoulders of the hole are dished. Like everything else, shear bolt holes can wear out.
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