Pto clutch and overrun

Farmall H, HV & Super H, 300 & 350, 1939-1958

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pokitisme
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Pto clutch and overrun

Postby pokitisme » Fri Mar 30, 2018 1:00 am

Well I'm thinking of getting me a PTO clutch and a PTO overrun. But an interesting idea popped into my head as I was thinking about this. Do I really need both of those items. Again I have a 1948 Farmall H. And if I do need both of those items in what order should they be placed on the PTO shaft from the tractor. Should it be the PTO shaft then the PTO overrun then the PTO clutch then the PTO implement. Or what. Seems to me like that's a whole bunch of stuff to add on to the end of the PTO shaft and I'm not sure about all of that stuff.
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Re: Pto clutch and overrun

Postby Urbish » Fri Mar 30, 2018 4:45 am

What are you going to be powering via the PTO? That will dictate what/if you need additional things on the PTO. As always, the simpler the setup, the fewer things there are to buy/break. Are you planning to mow with it?
Last edited by Urbish on Fri Mar 30, 2018 6:49 am, edited 1 time in total.

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Re: Pto clutch and overrun

Postby Shane Nelson » Fri Mar 30, 2018 5:37 am

The over run goes at the tractor end and the clutch on the other. You add both of those and you will probably have to shorten your pto shaft. Some are simple, some are not. Depends on if it has a piece welded on it or it’s a solid tube or trianglular shape.
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Re: Pto clutch and overrun

Postby John *.?-!.* cub owner » Fri Mar 30, 2018 8:55 pm

Yes, you DO need both. The clutch allows the pto to slip if the brush hog hits something solid. The over run clutch lets you stop without waiting for the pto to spin down, A five foot brush cutter will drive the tractor several feet with you standing on the clutch and brakes without the over running clutch. I have been in the tractor seat when that happened. Didn't take the fence down, but did bow it before I got stopped.
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Re: Pto clutch and overrun

Postby pokitisme » Fri Mar 30, 2018 11:55 pm

Well that's actually a pretty interesting question on what would the PTO be powering. Considering the options available I can only think of a very few limited items. In my case let me put it like this I have a brush hog which I have shut off and it did push me a few feet a slightly interesting shock but I had already read about that so I knew it was going to happen. But the guy I bought my brush hog.. blade... Three-point boom.. and dirt scoop off of also has a couple of post hole diggers I might try and get my hands on LOL. So for practical purposes it would probably be a brush hog and a post hole digger. I would think that the clutch would be a necessity as you never know what you might run over. The overrun though I believe could be counted as useless if you just stop the tractor and let the brush hog or PTO just idle down to a non spin. But as I'm thinking about this could some outside force affect the blade movement on the brush hog if the PTO is not running. I don't know I'm just brainstorming here. I would think if the PTO has been turned off that there would be no way to influence the transmission but if I remember correctly even with the PTO lever in the off position you can still turn the PTO my hand. And yes everybody I know to stay away from a moving PTO LOL whether it's engaged or not engaged. And to never engage it until the PTO shaft is firmly secured. Actually what I mean is never turn the tractor on until the PTO shaft is fully secured.
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Re: Pto clutch and overrun

Postby John *.?-!.* cub owner » Sat Mar 31, 2018 11:30 am

I am curious about what kind of clutch you are talking about. The pto has a shifter to disengage it. Are you thinking about an additional clutch in the drive line? I have seen slip clutches on brush cutter drive shafts, many of them have them from the factory, but never an additional clutch simply for stopping the pto drive line. As to the overrunning clutch, there is no way I would run a brush cutter on any tractor with out a live pto system without the over running clutch. You never know when something may run in front of tractor, pets, a fawn etc. ot there be a rock or stump you forgot about, that you may need to stop in a hurry, and the over running clutch/adapter, lets you do that.
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Re: Pto clutch and overrun

Postby Scrivet » Sun Apr 01, 2018 7:43 pm

pokitisme wrote:....... The overrun though I believe could be counted as useless if you just stop the tractor and let the brush hog or PTO just idle down to a non spin ............

You CAN'T just "stop the tractor and let the brush hog or PTO just idle down to a non spin"

What I think you are missing here is there are several factors, terminology, and situations involved and each one needs to be looked at individually to get the full picture.

1. The transmission is connected by gears to and drives the PTO shaft. The implement PTO power driveline is either engaged or disengaged, no give in it, just like a toggle light switch or being pregnant it's all or nothing.
2. An overrunning clutch is a one way ratchet, you can only "tighten" the power to the implement.
3. A slip clutch allows for the PTO driveline power to have "give" at the business end of the implement without breaking something.
4. An overrunning clutch and a slip clutch are two distinct items with totally separate independent functions.

With the H in as built configuration, the momentum/inertia/stored power/flywheel effect of the rotating brush hog continues after engine power is removed by depressing the foot pedal clutch. Since you have a direct connection from the transmission to the PTO driveline the rotation of the blades becomes the motor to drive the wheels. It's technically possible to break this connection by disengaging the PTO lever or kicking the transmission shifter out of gear, neither of which should be counted on in an emergency stop. (A.They are not natural reactions which would be to push the brake and clutch B. Pressure against the gears can make both impossible) An overrunning clutch, just like a ratchet and socket will only turn one way. Once the blades become the motor, just like your socket set, no power is applied the other way.

The slip clutch needs to be tight enough to power the implement but still have give at some point. If it's completely stuck or rusted up it's not a slip clutch. Older/cheaper made/simpler PTO drivelines will have a shear bolt instead of a slip clutch. A round shaft is inserted into a round hole on a mating shaft. A single hole is drilled crossways through both and a special bolt is inserted. When something stops the business end of the implement side of the connection, usually the round shaft side, the round hole shaft powered side spins around the now stopped solid shaft side breaking the bolt. You then have to remove/fix what caused the implement to stop and then line up the holes and install another special bolt.

One other thought about the brush hog powering the tractor... Without the overrunning clutch, in a panic stop where you're pressing the clutch and brakes, and pulling on the steering wheel to press harder on the pedals, and one wheel locks up. What happens??? All the power goes to the free wheel and you double your speed into what you were trying to avoid.

I totally disagree that the over running clutch is useless. However you are free to decide that it is useless if you want, if so just have the paramedics call me and tell me you do change your mind.

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Re: Pto clutch and overrun

Postby Indy4570 » Sun Apr 01, 2018 8:02 pm

I thought my clutch was out, I thought somehow I had simply worn it out or something had broken. pressing the clutch did nothing and the tractor kept on moving, as has been stated the brakes did nothing as my clutch was useless and my tractor still moved. This is because I did not have the over running item on the PTO shaft. I still dont have one for that tractor but I will before I use it to brush hog again. I do have those on 2 others now.

helpless to change events is what I would call the experience.
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Re: Pto clutch and overrun

Postby pokitisme » Tue Apr 03, 2018 1:50 am

Thank you guys so much for the info here. And that is why I asked. Is so I can get clarification on certain ideas and thoughts running through my noodle. Anyway I will research these items and their applications a little bit more thanks to your all's clarification. I did know that I could put a bolt through the PTO shaft coming from the bush hog to the PTO on the tractor. But I didn't know it was a sure bolt. I was just told it was an additional way to hook it up. Lots of interesting ideas there I will look into them.
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Re: Pto clutch and overrun

Postby Scrivet » Tue Apr 03, 2018 9:36 pm

pokitisme wrote:........ I did know that I could put a bolt through the PTO shaft coming from the bush hog to the PTO on the tractor. But I didn't know it was a sure bolt......
If you mean shear bolt, in that location that is NOT a shear bolt. The tractor PTO has splines and grooves. Take the bolt out and it will still spin just fine. A bolt installed there is only to keep the PTO from walking off the end of the shaft. This is usually accomplished with a push pin that fits in the round groove around the entire shaft in the splines about half way up the tractor PTO shaft. A shear bolt will be going through a smooth round shaft inside of a smooth round hole. A shear bolt is NOT any bolt you grab out of a coffee can on the shelf by the way. They are softer so they will break (shear off) when the "round hole" shaft end attached to the tractor keeps spinning and the round shaft like on a ninety degree gearbox on a brush hog stops suddenly because the blades hit a stump.


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