# Converting to C.V PTO Shaft



## PaMike (Dec 7, 2013)

I have a Rhino batwing that uses just a traditional PTO drive shaft. I do quite a bit on tight quarters mowing and the PTO really knocks and carrys on. Can I just buy a C.V pto end to go on the shaft? Anyone ever do it? My gut says I could do it but the geometry may not be 100% equal angle and I may still get a little noise but it should be a good bit better.

Am I correct?


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## mike10 (May 29, 2011)

To give you a little more incentive, the use of a standard drive shaft on a large cutter can result in damage to the tractor. The speed up and slow down of the ujoints, knocking, places a high load on the pto system. Have seen more then one tractor where the internal pto drive shaft snapped when using a cutter without the cv pto. Replacing the complete pto shaft will probably not cost much more then just the front section. With the cv you do not need equal angles from the tractor to the machine since the cv does what the equal angle does.


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## BWfarms (Aug 3, 2015)

I have a CV PTO shaft on my Bush Hog, it's nice and never a sound heard.


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## Tx Jim (Jun 30, 2014)

Or you could engineer & install an equal angle hitch for probably less $$$$. In reality most CV joints are only good for a 80° turn. Did I state I dislike CV joints because they're heavy & very expensive.


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## BWfarms (Aug 3, 2015)

Tx Jim said:


> Or you could engineer & install an equal angle hitch for probably less $$$$. In reality most CV joints are only good for a 80° turn. Did I state I dislike CV joints because they're heavy & very expensive.


If you're at 90 degrees, there's tire rub


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## PaMike (Dec 7, 2013)

mike10 said:


> To give you a little more incentive, the use of a standard drive shaft on a large cutter can result in damage to the tractor. The speed up and slow down of the ujoints, knocking, places a high load on the pto system. Have seen more then one tractor where the internal pto drive shaft snapped when using a cutter without the cv pto. Replacing the complete pto shaft will probably not cost much more then just the front section. With the cv you do not need equal angles from the tractor to the machine since the cv does what the equal angle does.


Yes, that's why I was considering it. I can hear the PTO shaft in the tractor knocking and making noise.

A CV pto is basically just 2 u joints that make an equal angle at the input so the rpm speed is uniform, but doesn't the rear ujoint still have a rotational speed change??

For an equal angle hitch to be designed how do you go about changing the hitch to get accomplish that?


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## mike10 (May 29, 2011)

For an equal angle pto to work, the distance from the end of the tractor pto shaft to the center of the hitch pin equals the distance from the center of the hitch pin to the end of the implement gearbox shaft. Ideally the pto shaft will be level, If the pto shaft is not level, then the angle at the tractor should equal the angle at the implement.

In the case of your mower, if it is 540, the distance from the end of the tractor pto shaft to the center of the pin hole in your drawbar is 14". If your mower is like most, then the distance from the gearbox input shaft to the hitch pin hole of the mower is closer to 24". You would need a drawbar extension of 10" for the equal angle setup.


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## glasswrongsize (Sep 15, 2015)

mike10 said:


> In the case of your mower, if it is 540, the distance from the end of the tractor pto shaft to the center of the pin hole in your drawbar is 14". If your mower is like most, then the distance from the gearbox input shaft to the hitch pin hole of the mower is closer to 24". You would need a drawbar extension of 10" for the equal angle setup.


Mike, I dang sure know better than to argue with your vast knowledge and I'm only trying to learn too, but...

If the PTO to pinhole is 14 and the pinhole to gearbox is 24. So, adding the two together, PTO to gearbox is 38; the middle of 38 is 19. To get from 14 to 19 would only be a 5" hitch extension?

With full respect, Mark


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## mike10 (May 29, 2011)

You would be right if you cut 5" off the mower hitch Since the gearbox shaft to the hitch pin hole is 24" you need 24" from the hitch pin hole to the tractor pto shaft. I know, it can get confusing.


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## glasswrongsize (Sep 15, 2015)

mike10 said:


> You would be right if you cut 5" off the mower hitch Since the gearbox shaft to the hitch pin hole is 24" you need 24" from the hitch pin hole to the tractor pto shaft. I know, it can get confusing.


Nope, that did it. The light finally came on. 

Mark


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## Beav (Feb 14, 2016)

I am still lights out


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## glasswrongsize (Sep 15, 2015)

Beav said:


> I am still lights out


I should let Mike explain it instead, but I will give it a shot (if for nothing else than test myself)

In my mind, I had to unhitch the tractor and mower; I parked them in the shade to work on them.

Go to the mower and measure from the gearbox on the mower to the hitch hole on the mower; that's gonna be our constant. In make's example, it is 24".

Now, walk over to the tractor and make it the same as the mower. In Mike's tractor's example, the tractor's hitch hole was 14" from the PTO. To make them the same (24"), you will have to move the tractor's hitch hole back by 10" to achieve the 24" goal. Once done and hooked back up, this will put the hitch pivot point directly in the middle---halfway between the U-joints.

I had to unhook them in my head to get it to make sense that I just had to make both of them the same.

Mark

PS, I had to some extra welding to make the hitch extension strong enough; I also had to go buy a new PTO shaft because my old one was 1/2" too short now to safely span the extra 10"....but it was all in my head, so it didn't take too long or cost too much.


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## Wethay (Jul 17, 2015)

If the drive shaft and driven shaft are parallel the shaft between spans the gap with both u joints at the same angle, and if phased right they cancel each other out. When the are cancelling each other out the first joint speeds the shaft up, then slows it down as it flexes, the second joint does exactly the opposite so the driven shaft remains at a constant speed. If both joints are not at the same angle they don't cancel each other out. If the pivot point is closer to one joint than the other the joints do not flex at equal angles. Leave your pto off and turn the tractor as sharp as you can without damage and you should be able to see the unequal angles of the joints.


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## Tx Jim (Jun 30, 2014)

BWfarms said:


> If you're at 90 degrees, there's tire rub


I'll rephrase my statement with what I've experienced even in less than 90° turns ""expensive CV joints"" with ample grease applications seem to fail more often than regular u-joints utilizing an equal angle hitch.


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## Tx Jim (Jun 30, 2014)

mike10 said:


> You would be right if you cut 5" off the mower hitch Since the gearbox shaft to the hitch pin hole is 24" you need 24" from the hitch pin hole to the tractor pto shaft. I know, it can get confusing.


mike10

Very good point you made about implement hitch length that I failed to consider. :wub:. But adding a carrier brg in driveline on cutter although would be expensive would solve hitch length problem

Jim


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## mike10 (May 29, 2011)

I thought about the carrier bearing but on a pull type rotary cutter where the hitch moves up and down, the angle of the cutter shaft would not be pointing straight at the tractor pto shaft so the angles could never be equal. I know some cutters use a carrier bearing mounted on the deck, but you still have the problem equal distance from cutter to hitch to tractor.

The killers of cv joints are lack of grease at the cv prart of the joint and the tractors lift arms. Repairing standard ptos is not cheap either

The biggest problem with equal angle ptos is the drawbar extension many use. I was never so happy as when NH did away with that extension and went to cv joiints


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## Tx Jim (Jun 30, 2014)

mike10 said:


> The biggest problem with equal angle ptos is the drawbar extension many use. I was never so happy as when NH did away with that extension and went to cv joiints


So don't you think a CV joint driveshaft changes angles going over rough terrain similar to non CV driveshaft? IMHO equipment operators not desiring to install/utilize EA drawbar extensions is one of the reasons equipment manufactures went to CV joints. All pto repairs are expensive but a regular u-joint won't warm up the cost of repairing a worn out CV joint plus CV joint are heavy to attach to tractor pto shaft for an OLD MAN such as I.


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## mike10 (May 29, 2011)

Yes, they change angles. What I was referring to on the mower is if you put a bearing support on the tongue of a mower the hitch point always stays the same height, but the back of the hitch goes up and down with the machine. This will change the angle of the end of the jack shaft to the tractor up and down.

I agree the reason for the cv joints was to get away from the hitch extension, but you can not deny that the cv joint is better at eliminating the vibration from drive shaft in turns. While the equal angle setup is good, it does not equal the cv joint.

I also agree with the weight issue and would add it is a messy job hooking the shaft to the tractor, at least if the cv joint has been maintained like it should be. One solution is to go 1000 rpm,, the shafts are smaller.


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