PTO clutch slipping?

[quicksandfarmer]

I noticed something that has me scratching my head a little and I'm interested in any input.

Recently, I ran over some electric fence wire with my rotary cutter and made a mess of it. I eventually was able to get the wire out by hammering the blades of the cutter. What has me puzzled is that I thought I would be able to immobilize the blades of the cutter by engaging the PTO with the engine off, and engaging a drive gear and blocking the wheels. However, when I hammered on the the cutter blades the driveshaft would rotate.

The cutter has a shear bolt, no slip clutch, so I have to think that the clutch is slipping. What's weird is that there's no indication in use that the clutch is slipping. While I've never broken a shear bolt, I have stalled out the tractor by mowing tall grass in high gear or by running over rocks.

It seems to me that the only place the PTO drivetrain could be slipping is the clutch. Or am I missing something? Is this something I should be worried about?

Thanks.

 

[greg_g]

If you're positive you left the PTO engaged, you could actually be turning the engine. That's kinda dangerous, in that you could theoretically start it. Leaving the transmission in gear and setting the brakes should remedy that.

If all that's been done already, it does pretty much point to the PTO clutch.

//greg//

 

[Soundguy]

Does this model have a built in ORC? inside the gear housing of the tractor? I've seen some tractor designs incorporate this.. like kubota.. etc. The chinese are real good at copying designs... maybee they picked up that one too??

Soundguy

 

[3RRL]

It could be possible I suppose, but I doubt you are turning over the tractor motor. There's too much down gearing in the PTO, tractor trans and mower gear box, IMO...but anything is possible?
When you were able to turn the blades, did they spin around all the way? Like they could spin freely? Perhaps you did not move them enough to feel the "stop" provided by the engagement? What about the possibility of the mower gear box being broken or something else broken? PTO shaft etc.? Did you run it after you got the wire off to see?

 

[quicksandfarmer]

I ran it after I got the wire out and it seemed fine. While I was working on it there was some resistance to turning, but not enough to hold the blade still while I hammered on it. When the PTO is not engaged I can easily turn the mower shaft with my hands.

I was just kind of surprised, there is no indication during operation that the clutch is slipping, so I thought I would be able to hold the mower still to work on it. I also use a pto-driven chipper, and if I jam that the belts will smoke before the clutch slips.

 

[greg_g]

It could be possible I suppose, but I doubt you are turning over the tractor motor. There's too much down gearing in the PTO, tractor trans and mower gear box

No, if you think about it - it's actually "gearing up". Roughly 2200 engine RPMs are geared down to produce 540 PTO RPMs. Turning the PTO shaft then, is sorta like using a reduction gear to turn the engine.

And if the transmission is in neutral, it's not going to provide any additional resistance. If the tranny was in gear - and enough force was applied to the mower blades - the tractor would move. Remember the older tractors that got pushed down the hill by the kinetic energy of spinning bush hog blades? That's what prompted folks to go out and buy an ORC for the PTO spline.

//greg//

 

[xlr82v2]

What tractor do you have?

 

[greg_g]

What tractor do you have?

He's talking about a 35 horse four wheel drive straight gear Jinma

//greg//

 

[3RRL]

Yeah, I suppose you're right Greg. It could happen if it was in gear then.

 

[SPYDERLK]

No, if you think about it - it's actually "gearing up". Roughly 2200 engine RPMs are geared down to produce 540 PTO RPMs. Turning the PTO shaft then, is sorta like using a reduction gear to turn the engine.
//greg//

3RRL was right. Think of it this way- if you turn the PTO once the engine is going to have to spin about 4 times. Thats a mechanical disadvantage from the PTO end.

larry​