PTO Over run Clutch

Chris (UK) · May 28, 2009

Hi folks. Got a question regarding over run clutches and there is bound to be someone out there who can help? I fitted one last year to use with a rotary grass topper, having read on this site that it was necessary for safety. My PTO brake doesn't work - to repair means splitting the tractor and I thought I'd leave that until something else needs doing on the back end. Consequently, with the PTO disengaged, the shaft still turns although it's not being driven. Cant use a cover because it sticks out too far and is a larger dia. than the Shaft cover. Anyway, the long and the short of it is I caught my pants (trouser) leg on it last week which could have been nasty! My question is if you are using a topper/mower/bush hog etc. which rotates in a horizantal plane, without an overrun, how can this push the tractor forward? I could understand it with something rotating in a vertical plane which could act like another driving wheel, but not horizantal. Is there anybody out there who could explain it please?

Many thanks, Chris.

Fordfarmer · May 28, 2009

It only happens on tractors with a transmission-type PTO. Since the PTO is driven off a shaft in the transmission, the inertia of the blades can 'backfeed' the PTO and then the transmission... keeping you moving after you push the clutch in. It wouldn't happen if you have live PTO or independant PTO. (sounds like your tractor has independant, so a ORC isn't needed for preventing the brush hog from pushing the tractor, but is still a good idea to save the brake... when it gets fixed.)

JDemaris · May 28, 2009

That applies to tractors with transmission-driven PTOs, not tractors with live or independent PTOs. With a trans-driven PTO, the momentum of the mower backfeeds to through the transmission and keeps the tractor moving, even when the cluth is pushed in.

The overrunning clutch stops that back-feed.
Also, an overrunning clutch used on a live or independent PTO tractor can stop the PTO brake from getting torn out.

rustyfarmall · May 28, 2009

Older tractors had the PTO more or less coupled directly to the transmission, and those tractors DO NEED the over running clutch when running a machine such as you describe. Newer tractors powered the PTO independently of the transmission, and do NOT need the over running clutch. 1955 or so seems to be the breaking point for US built tractors, but that changeover did not include ALL tractors. Some got it sooner, some got it much later.

Basically, if you have to depress the clutch pedal to engage the PTO, you need an over running clutch. If the PTO can be engaged by simply moving a lever, you probably do not need it.

souNdguy · May 28, 2009

I agree with the others. a spinning mass is a spinning mass. what plane it spins in makes -0- difference if it is coupled to a non live trans driven pto, which can backfeed the trans and drive wheels even witht he clutch down ( you'd have to snatch it out of gear to stop the backfeed ).

I like the orc on the pto brake models.. as the others said. it saves the brake.

My sugestion is to get a quick disconnect push button style orc so you can remove it with the mower.. in the mean time .. with no pto brake, and if yors is indepent ( likely is if you have a brake ).. then you can just remove the orc for now.

soundguy

Chris (UK) · May 28, 2009

Thanks a lot guys. Very useful info. I have IPTO so for the time being will take the ORC off. I prefer to have two legs! Thanks again.

J.C.in AZ. · May 28, 2009

You're back. Good to hear from you.Stay in touch,some of us welcome your advice.JC

John B. · May 28, 2009

When you're mowing the engine is the driving force. When you press in the clutch you seperate the transmission from the engine. The PTO and transmission still stay meshed together thus the mower becomes the driving force until all the momentum is used up from the spinning blades. They act as a flywheel. This is why they invented the overrunning clutch. It's called a sprag in automobile automatic transmissions. It's also used in the front hubs of 4-wheelers to lock in the 4 wheel drive.

Tx Jim · May 29, 2009

JDemaris,
Glad to see you post again. Jim

Sam#3 · May 29, 2009

I"m an old man and still have all my fingers and toes even after working around some nasty equipment.
Once, long ago, I was working in a grain elevator/feed mill which had most of the equipment driven off a line shaft. The shaft had been reconfigured over the years and had a collar with a long setscrew left on it. One day the "head miller" caught the hammer loop of his overalls on the setscrew. Except for being sore for a couple days he escaped injury. His old overalls were ripped to shreds and his watch had been squeezed so that the main stem was protruding from both sides.
Since then I"ve been leary of rotating equipment. I still run a brush cutter with my old Case but I don"t get off the tractor until everything stops turning. I don"t even trust the blades.
Be careful.

Roy Ward · May 29, 2009

Smart man. Over run clutches are a very good idea and I use them. But until that cutter stops there is danger.

PTO Over run Clutch

Chris (UK)

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Fordfarmer

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JDemaris

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rustyfarmall

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souNdguy

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Chris (UK)

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J.C.in AZ.

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John B.

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Tx Jim

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Sam#3

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Roy Ward

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