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Tractor Talk Discussion Forum

Bush Hog clutch/shear pin

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John in La

07-11-2010 10:43:42

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I have a Bush Hog Model 502 brush cutter with removable side panel that came with my tractor when I bought it. The tractor is a Ford 861 diesel and is rated at about 40 PTO HP.
I have found out that it originally came with a clutch in the PTO driveline but the original owner replaced the PTO shaft for some reason and did not put any kind of overload protection in it.

I am on the fence on how to fix this problem but know I need to do something. Since the input shaft of the cutter gear box is splined I can not use a normal shear pin.

So now I feel my options are a clutch....

or a shear pin type yoke.

I really do not want the clutch because I am afraid of seizing up over time from being out in the weather but some people have said this would be my best choice because it does not have any shear pins to worry about.

My problem is I do not know anything about PTO drive line ratings and or what system to buy.
I see metric shafts; different class ratings; ect.. and need some help deciding what to buy.

So what class/inch lb rating should I be using on a 40 pto hp tractor??
I would like to cut down and reuse my old shaft but do not know what to look for to get matching parts. I might even consider a whole new shaft if the difference in price over piecing this old shaft to a new over load protection is not to much.

Thanks for any and all help.

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John A.

07-11-2010 21:46:22

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 Re: Bush Hog clutch/shear pin in reply to John in La, 07-11-2010 10:43:42  
John, I have run shredders all my life, Shear bolts is old school, Personally I will not have a shear bolt set up, I do require a lot from a shredder so I would spend most of my time replacing bolts! A slip clutch is a lot more forgiving, put your fears at ease by simply backing off the tension bolts about 1 or 2 turns in the fall after you put it up till spring, Then in the Spring hook up, service, mow a little till the clutch slips just enough to get rid of any rust that may have formed over winter, then retighten the 1 or 2 turns you took off back in the winter. Then give her h3ll.
Also since most older shredders do not have a shield/cover use a old 5 gal bucket or #2 washtub turned upside down to help keep rain, snow away from the slip clutch. Hope this helps!
John A.

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07-11-2010 17:08:16

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 Re: Bush Hog clutch/shear pin in reply to John in La, 07-11-2010 10:43:42  
Most all those clutches whether they be slip, or shear, will handle 40 hp, no problem. The ones that are yellow, like the ones in your pictures are able to handle 40 HP, no problem. Most of the yellow ones that have the circle in a triangle shape are metric, and made over seas, somewhere. Here is a link to Agrisupply, about the only thing you need to know is the length of your existing PTO shaft, and order one a little longer than the contracted length, that way you can trim it a little to fit your needs. Never run a PTO shaft that is fully contracted, when hooked up, or extended so that there is less than 6" of overlap.

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07-11-2010 13:25:35

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 Re: Bush Hog clutch/shear pin in reply to John in La, 07-11-2010 10:43:42  
Go with the shear pins, weather won"t hurt them and they are very inexpensive. If you break one (sometimes I go all season and don"t) you can almost replace it by hand. Buy a pack of extras, toss them in the tool box and get to work.
BTW I have a Bush Hog brand six foot behind a 35 HP IH

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07-11-2010 12:55:12

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 Re: Bush Hog clutch/shear pin in reply to John in La, 07-11-2010 10:43:42  
T= HP x K/ N, where K =5252, N =RPM, HP = HP and T = Torque, hp x 5252/N~lb-ft. Since you want to transmit 40 hp at 540 rpm( your typical pto shaft design speed),

T = 40 x 5252/540 =389 lb-ft.

I would not be afraid of using a slip clutch as you can take it off, back off the adjusting nuts and leve the clutch loose and store it inside. But it"s your $"s and your choice.

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07-11-2010 22:41:31

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 Re: Bush Hog clutch/shear pin in reply to Jerry/MT, 07-11-2010 12:55:12  
Correction K= 1/5252

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