# What is a PTO overrun clutch & do I have one?



## Puck Head

I just bought my first tractor and need to l need to learn about it. What is this PTO overrun clutch and how do I know if I have one? Why do you need it for a bush hog? My lift leaks down when you shut the tractor off. Is this normal?
Thanks for any help you good people can give me.


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## Fordfarm

The Over Running Clutch (ORC) is a MUST for operating the N tractors! Since they have a PTO that is driven by the transmission, any inertia built up by the implement (Brush hog, mower, etc) will be transfred BACK to the tractor via the transmission EVEN WITH THE CLUTCH DEPERSSED. Using an ORC will prevent you going through fences, buildings, ditches, etc, when you try to turn corners or stop. They are available at any TSC (be sure to get one the right size for your PTO shaft) and slide onto the PTO shaft. They are held on by a roll pin through the hole in the shaft. I use one on mine, no matter what PTO driven implement I am using. Just added security! 
How long does the lift take to leak down? A NORMAL, new or just rebuilt system will not leak down, but 90% of them do, now after 50+ years! I would recommend draining the fluid and doing a diesel flush. Got a manual yet? they are good to have around! Get it at TSC I&T F-04 - well worth the price. 
Welcome to the Board! DON'T FORGET TO POST PHOTOS!


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## Fordfarm

Photo of an ORC installed on The PTO of my 1949 8N.


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## Drawbar

We ran an old 900 Ford without an Overrunning PTO Clutch and what a ride it was. You would shove in the clutch, and the momentum from the spinning bushog blades would drive your tractor ahead another 30 feet!

Man you had to watch out/ plan for that little nasty surprise. If you were lucky, you could kick it out of gear, but that in and of itself was a challenge of your tractor operating skills as you swerved around trees and rocks and other obstructions.

If you do not have an Overrunning PTO Clutch mechanism, you will know it quickly. And if you don't, for your own safety, go out and buy one. We should have years ago. Now we have a more modern tractor that powers it PTO without the use of the transmission.


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## Live Oak

Welcome to Tractor Forum Puck Head! Looks like the guys already have you taken care of. :thumbsup:


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## John-in-Ga

Hi, Puck Head and Welcome to Tractor Forum. I think the guys must have got excited in answering your first question and forgot your second. 

Most all lifts leak down when the tractor is shut off. Some leak a little faster than others. If yours isn’t leaking down fast enough to cause a problem; enjoy using your tractor as is. 

It is a good safety practice to lower the lift when you park the tractor if there is an implement attached. This will prevent something or someone that is dear to you from being injured by the lift lowering either from leaking down or being accidentally lowered by someone inadvertently hitting the lift control lever.


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## Drawbar

Hey John in Ga,

You are right, I did not see that second question at all. Now having the 3 point hitch lower itself to the ground is pretty common, the amount of time it takes to do that indicates how much leakage you have in the hydraulic system.

On our old tractor, it fell rather quickly after being shut off because the hydraulic pump, cylinders and related gear were worn and could not maintain the pressure with the pump not turning. Now that I have a new tractor and everything is tight, my 3 point hitch (and loader for that matter) stays in place overnight or longer. Realizing this, you can get an idea if your system needs servicing, or is merely just worn.

For safety however, like John in Ga says, you should lower all implements to the ground. In my case this means the loader, 3 point hitch and anything else that is gydraulicaly driven. After I shut off my tractor, but before I get off, I cycle my hydraulic controls through all the functions. I do this because sometimes just because a piece of equipment is on the ground, does not mean other functions can't move with gravity. By clycling everything, you are assured everything that can be moved by gravity, has been moved.

In my case, this means my bucket. Yeah the loader is down on the ground, but if the bucket is rolled back, the weight of it could roll downward via gravity. By cycling the controls after the tractor is shut off, nothing can move anymore.

I am probably over-explaining myself here, but as a former Safety Coordinator, I take a keen interest in safety.


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## Puck Head

Wow. Thanks for all the responses. I will go back(I just came from there) to TSC and pick up the pto clutch.
I only have a blade right now but I tried to put a bush hog up to it and maybe I didn't do something right but I don't think the lift was picking it up. It takes about 10 minutes for the blade to lower when the engine is shut off. Is this as fast as it seems?
How hard is it to rebuild the lift and do I need any specialty tools? I have lots of tools and a cement floor garage with air compressor.
Nice to meet everyone and thanks for all the help.
I will load photos as soon as I figure out how.


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## Drawbar

Ten minutes isn't too bad. I mean it certainly indicates some internal leakage, but from you post it sounded like you shut the tractor off and it settled right down to the ground. That's not the case so that is good.

The best way to describe it, is to put it in perspective. You have presurized oil trying to hold up a 500 pound object. When the engine is shut off your tractor is trying to hold that object up. The problem is, the weight of the blade is putting pressure backwards through the system. That heavy blade is compressing the oil so now every seal, every o-ring, and the clearances inside the pump must all resist that pressure.

Even a new tractor will eventually lower that blade to the ground. But because a new tractor has tighter seals and a pump that has not had any wear, it will take awhile to do so. An older tractor with a worn pump and seals will naturally allow more oil to squeeze by and thus lower the implement to the ground. In your case, that takes place in 10 minutes. On my old Ford 900, that was the case as well.

Myself I would not worry about it. The reason I have explained so much here is so that you can learn a little something about hydraulics. I am not trying to be smart here, or belittle you, I just like people to understand WHY things occur. Myself I would have someone explain things in simple terms so I can grasp it, then not explain anything at all.

As for repairing the hydraulics yourself. I would probably not recommend it. No offense to your mechanic skills, but hydraulics require a lot of patience, skills, and a super, super, super clean work area. If that does not scare you, then consider the fact that you have 40 or so horsepower being squeezed through tiny holes held in check only by tiny o-rings. Its easy to screw things up, and parts get expensive.

I got a lot of experience repairing hydraulic systems when I worked on the railroad in the Maintenace of Way division. With that in mind, I doubt I would even tackle this problem.


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## Puck Head

Thanks for the great answer Drawbar. One more question. Can I remove the pump to save some duckies or do I need to take the tractor to a repair service and have them R&R it. Your right I have little experience with hydralics.


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## Drawbar

Oh heck, my Bassett Hound could take the pump off if he had thumbs. That part is easy and is straight forward. What I was referring to was replacing the o-rings and stuff inside the spool valves and pump itself. Those things have super tight tolerances and stuff, but to take the pump itself off, or to unbolt spool valves from the tractor chassis, by all means grab some wrenches and go for it...

Well do yourself a favor. Write out a diagram of what line goes where and any kind of reference points on how the pump is mounted. Now I say this not because you are a little green at hydraulic mechanics, ALL good mechanics make sketches because what is clear in your mind now, gets a little fuzzy when you get the pump back from the hydraulic mechanic.

Good mechanics know sketching out lines and wires on paper for future reference is professionalism, not cheating.


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## Puck Head

Ok. So now I have the pump out. Where is the best place to take it for rebuilding and how much will it cost?


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## claudester

> _Originally posted by Fordfarm _
> *Photo of an ORC installed on The PTO of my 1949 8N. *


Nice clear picture. I see in the operators manual that there is a PTO safety shield but my tractor didn't come with one and I can't seem to find one on the net. Any insight on this?
Thanks


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