Shear pin misery... only thing left is adding a slip clutch?

[rd_macgregor]

The problem with clutches is they freeze up. If the unit sits for a while, it takes much more effort to break them loose and the tractor may be damaged.

This problem is exacerbated by outside storage. Each season, before first use, the unit needs to be backed off, then reset to the right slippage...otherwise you risk working with a totally seized (non-)slip clutch.

 

[N80]

I cannot imagine starting any spinning device with any mass to it at any speed higher than idle.

 

[wagne223]

I cannot imagine starting any spinning device with any mass to it at any speed higher than idle.

^^^^^THIS!!!

 

[hawkeye08]

It might just be me, the the holes for the shear bolt do not look the same size, likely just the way the picture is showing it, but critical that the bolt fits with no play in either hole. Any play will allow the two parts to start working on the shear bolt and before long, it fails all the time.

 

[Dadnatron]

hawkeye, they are the same. That must just be the pic. I can get it tight, and without any movement. But, the shaft is by definition to small for the HP of the tractor and the machine.

I'm going to look for a new shaft with a clutch. Perhaps a new shaft with a shear bolt of the appropriate size will work as well. But I know that this shaft is a Series 3 which is for HP of 20-25hp. At least according to the U-bolt measurements. At least according to this PDF.

JD instruction manual says to push RPMs to 'PTO speed' prior to engaging PTO.



Determining Your PTO Series - PaulB Parts - Ag, Industrial, and Mechanical Supply

 

[rustyshakelford]

hawkeye, they are the same. That must just be the pic. I can get it tight, and without any movement. But, the shaft is by definition to small for the HP of the tractor and the machine.

I'm going to look for a new shaft with a clutch. Perhaps a new shaft with a shear bolt of the appropriate size will work as well. But I know that this shaft is a Series 3 which is for HP of 20-25hp. At least according to the U-bolt measurements. At least according to this PDF.

JD instruction manual says to push RPMs to 'PTO speed' prior to engaging PTO.

View attachment 515056

Determining Your PTO Series - PaulB Parts - Ag, Industrial, and Mechanical Supply

I can see how you could some to the conclusion but they aren't being very clear. PTO should only be engaged at the minimum rpm so the tractor doesn't stall. Anymore and your cooking your pto clutch and impliments. Take the 5 sec to idle down, engage pto and bring it up to rated speed then.

It will be much easier on your equipment and you don't want to deal with a bad pto clutch

Brett

 

[SPYDERLK]

The problem with clutches is they freeze up. If the unit sits for a while, it takes much more effort to break them loose and the tractor may be damaged.

I cannot imagine starting any spinning device with any mass to it at any speed higher than idle.

The force to shear a bolt is very high but operating over only a couple degrees of rotation - - not much energy required to shear. Even a "frozen" slip clutch will almost universally break free at the force taken to shear a bolt. Typically a clutch can be set much softer than a shear bolt because its set torque will maintain thru many revolutions, absorbing lots of energy while the hi torque impulse resolves. A slip clutch system really doesnt require low rpm starting, but youre wearing things unnecessarily. Who would choose to do that? ... Well, maybe occasionally to force a little slip and exercise the clutch. ~ Automatic maintenance. :cool2:

 

[k0ua]

hawkeye, they are the same. That must just be the pic. I can get it tight, and without any movement. But, the shaft is by definition to small for the HP of the tractor and the machine.

I'm going to look for a new shaft with a clutch. Perhaps a new shaft with a shear bolt of the appropriate size will work as well. But I know that this shaft is a Series 3 which is for HP of 20-25hp. At least according to the U-bolt measurements. At least according to this PDF.

JD instruction manual says to push RPMs to 'PTO speed' prior to engaging PTO.

View attachment 515056

Determining Your PTO Series - PaulB Parts - Ag, Industrial, and Mechanical Supply

Yes but it doesn't say pop the PTO into engagement at full RPM. That just doesn't make any sense. When we used to all drive stick shift cars did we wind the engine up to freeway speed and then pop the clutch?.. well some of us did that as teenagers, but we usually weren't paying for the repairs. No we came just off of idle and gently engaged the clutch with the minimum "slam bang" needed to get the car rolling and then we increased throttle gently.

Things that are in manuals are not always clear, and keep in mind the guy that wrote the manual, likely has never operated a tractor.

 

[IslandTractor]

Slip clutches are a royal PITA and should never be needed on a belt driven flail mower.

 

[Jerry/MT]

I do not bring it up from idle. That is not a feasible situation in my real world. I cannot idle down every time I want to begin mowing.

I have no strange noises. Everything begins and appears fine. It begins spinning, and everything is smooth, but I think the stress of getting all that metal moving simply overcomes the shear force of the pin.

I am extremely limited on what I can add as far as size of a bigger bolt. There simply isn't very much 'meat' to drill out and maintain integrity.

If I try to weld it (and I'm not sure whether it is cast steel or iron) and add an adaptable slip clutch at the machine, will that 'work' as far as protection of the tractor? I was able to find a slip clutch at TSC which slips over the shaft at the gear box, and onto which the PTO shaft can be attached. At least that is what it appears to be set up for. I thought, perhaps if I weld the 'shear pin pieces' together, then I could still protect things with the clutch. Any thoughts about this?

The only other thing I can do is to purchase a completely new PTO shaft with a slip clutch integrated already. This is probably what I should do. Get a new PTO shaft Series 6 or 8 with a CV joint and a slip clutch. I am sure this would cure 'all' the problems which have arisen.

IF anyone has a recommendation on where I can find such a shaft collapsed length of 72" with at least 18" working expansion, please link me or give me a name. The length that is required is making it difficult to find.


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Even using a slip clutch will require you to fine tune the clutch setting so it's loose enough to take the start up torque loads and still function when your just cutting. I have a 6 ft rotary cutter with a slip clutch and I use a ORC to save the pto clutch on my tractor. I always start the mower at idle to minimize the shock loads on the tractor PTO system. I don't know why you think that's a hard thing to do. Once I start the cutter I keep it running until I'm done mowing, throttle back to idle and then disconnect the pto. the ORC doesn't allow the rotor inertia to feed into the pto clutch. Most of the vibration I encounter is due to the unfolding of the cutter blades ( they fold during shutdown due to the stopping inertia). A larger shear pin or a slip clutch are your only alternatives. Flail cutters, if balanced correctly, are probably more vibrationless that two bladed rotary cutters.