Have you slipped your PTO shaft clutch for the year?

[Elliott in GA]

Since people often post reminders about routine things, here is mine. I slipped my rotary cutter's PTO clutch last weekend; and therefore, I am set for another year. The process was simple and painless - just a bit tedious (working on eight bolts through the PTO shield access ports). However for me, I would much rather spend some time on a day (sunny cool spring day) of my choosing instead having to replace a shear bolt while working on a hot summer or cold winter day.

 

[SDT]

Since people often post reminders about routine things, here is mine. I slipped my rotary cutter's PTO clutch last weekend; and therefore, I am set for another year. The process was simple and painless - just a bit tedious (working on eight bolts through the PTO shield access ports). However for me, I would much rather spend some time on a day (sunny cool spring day) of my choosing instead having to replace a shear bolt while working on a hot summer or cold winter day.

No, but all 6 of mine are on the list of things to do.

I plan to go back to shear bolts on any future mower purchases.

SDT

 

[GeoHorn]

You may not have a shear bolt on some clutch-equipped shredders….
If the clutch is frozen you won’t shear a bolt …you’ll shear a gearbox or PTO drive.

 

[mcfarmall]

I could change several shear bolts in the time it take to fiddle around with the spring bolts, find a tall stump to stall the mower blades, blah, blah, blah. If it didn't cost a small fortune I'd switch over to a shear bolt. Slip clutches are perfectly suited for rental equipment.

 

[SDT]

I could change several shear bolts in the time it take to fiddle around with the spring bolts, find a tall stump to stall the mower blades, blah, blah, blah. If it didn't cost a small fortune I'd switch over to a shear bolt. Slip clutches are perfectly suited for rental equipment.

Agreed.

I made the change to slip clutches a few years ago and regret it.

Will change back to shear bolts (when possible) over time.

SDT

 

[SDT]

You may not have a shear bolt on some clutch-equipped shredders….
If the clutch is frozen you won’t shear a bolt …you’ll shear a gearbox or PTO drive.

Agreed.

I consider either shear bolt or slip clutch protection as protection for tractor internals rather than mower gearbox protection.

A corrosion locked slip clutch is neither.

Equally important, and overlooked by just about everyone: An improperly adjusted slip clutch is no protection for tractor internals. To effectively protect tractor internals, a slip clutch must be adjusted to the PTO HP rating of the tractor with which it is used. Who does that?

SDT

 

[jyoutz]

Agreed.

I consider either shear bolt or slip clutch protection as protection for tractor internals rather than mower gearbox protection.

A corrosion locked slip clutch is neither.

Equally important and overlooked by just about everyone: An improperly adjusted slip clutch is no protection for tractor internals. To effectively protect tractor internals, a slip clutch must be adjusted to the PTO HP rating of the tractor with which it is used. Who does that?

SDT

So what is the process for adjusting a slip clutch to the pto hp output?

 

[D2Cat]

So what is the process for adjusting a slip clutch to the pto hp output?

If the slip clutch is adjusted (too tight) for a higher PTO HP tractor the clutch will not slip when used on a lower HP machine, and therefore of no use for any protection.

 

[North Idaho Wolfman]

So what is the process for adjusting a slip clutch to the pto hp output?

The process to adjust it depends on the type, there are a few.

 

[SDT]

So what is the process for adjusting a slip clutch to the pto hp output?

Good question, the answer for which you will not find in the manual that came with your mower.

The proper technique is a trial and error method that will take time. Accordingly, just about no one does so.

SDT

 

[Elliott in GA]

Just to provide some perspective, I followed the LP manual's instructions for slipping the PTO clutch (loosen all PTO bolts two turns, slipped clutch verified by marks and retighten all PTO bolts two turns). The PTO clutch was working before I slipped it (did not allow slippage under normal operation but provided slippage during hard contacts - I have had a couple reclaiming a field), and it is back to where it was.

The PTO clutch friction/compression is not some highly precise setting. It just needs to be enough to allow normal operation with the ability to slip under a high stress situation - that is a very large envelope of acceptable adjustment. To be on the safe side, you would want to always be adjusted towards the lower end of the envelope (regardless of PTO HP). If you notice slippage during normal operation, you could tighten it to resolve it.

Cutters that use shear pins typically use one type of pin regardless of the tractor PTO rating (so long as it is within the appropriate range for the cutter).

There is no right choice between slip clutch and shear pin; each have their own benefits and problems. I prefer a slip clutch on a rotary cutter (high probability of a hard strike), but I have shear pins on my finish mower and spreader (low probability of a hard strike/blockage). Shear pins do not always work as expected either (breaking too easily or not at all); they are not a high quality control precision made product.

I wonder how many shear pin protected PTOs have rust on the mating surfaces/flat ends of the shafts at the shear pin? Would that impact the amount of force required to break the bolt?

The point of the post was a reminder to service your PTO slip clutch, and you should also periodically inspect/disassemble your shear pin link too - unless you have replaced it within a year or so.

 

[Crummy]

I slip mine as it's cheap insurance but I question if it's really needed if the implement is stored inside and has not been exposed to any inclement weather.

 

[GeoHorn]

A possible method to adjust a slip clutch is to deliberately locate an area of grass/brush/etc that is “too high” for anywhere you expect to mow…. and adjust the clutch loosely …and make a trial cut and the fwd speed you expect to use the shredder/mower.. It will hopefully not cut cleanly because the clutch is slipping. Then tighten the clutch bolts a turn or two….and try another mowing run.
When you have the clutch bolts tightened ”just” until a clean cut is obtained in grass slightly higher than you ever expect to mow…. you will be at what I believe to be a “safe” tension-setting on the clutch. Important: keep track of how many turns you loosen next year when you “slip the clutch” so you can return them to the preferred place.)
Hope this helps (and makes sense.)

YMMV

 

[Nicfin36]

I too hate fiddling with the slip clutch, most particularly the tiller, as it is a pain to access easily. I don't adjust mine until later in the year as all I till right now is for green fields. I have to get off about 3 times to tighten the slip clutch until it quits slipping. I'll think I have it, and nope, it will be slipping. It truly is a pain.

The bush hog slip clutch on my rotary cutter is much easier as it is much more accessible and seems to be more forgiving set loose, until I hit tall thick grass.

 

[NCL4701]

Thanks for the reminder. Only shear bolt I have for the rotary cutter is in the rotary cutter. Need to pick up a couple more.

 

[MattN03]

I slip mine as it's cheap insurance but I question if it's really needed if the implement is stored inside and has not been exposed to any inclement weather.

I wonder the same thing. I didn't slip the clutch on my tiller this season since it's never been in the rain and never sets out. The slip clutch worked perfectly last week when I got into a little bit of rock while tilling FWIW.

 

[GreensvilleJay]

Surface rust on shear bolts won't really affect their performance specs. While 'technically' the change from steel to iron oxide should reduce the strength, it's very,very minor and arguably 'rust welds' are dang strong so the 'teetertotter' stays about level.
Anyone with a walkbehind snowblower KNOWS how impossible it is to remove a flat tire cause the lynchpin is rustwelded' to the axle and removing an auger shear pin is 'fun'.....
It is a good idea though to spray or coat the bolts/nuts/connections with oil or grease, once in awhile.

 

[torch]

I wonder how many shear pin protected PTOs have rust on the mating surfaces/flat ends of the shafts at the shear pin? Would that impact the amount of force required to break the bolt?

Good point -- but one difference between clutches and shear bolts is that shear bolt connections can be greased.

I imagine that shafts running through sleeves (eg: snowblower augers) are more susceptible than mating flange connections (eg: PTO shafts), just because of the vastly increased surface area. But then, they are more likely to have grease zerks too, so it may be a wash.

 

[Elliott in GA]

Surface rust on shear bolts won't really affect their performance specs. While 'technically' the change from steel to iron oxide should reduce the strength, it's very,very minor and arguably 'rust welds' are dang strong so the 'teetertotter' stays about level.
Anyone with a walkbehind snowblower KNOWS how impossible it is to remove a flat tire cause the lynchpin is rustwelded' to the axle and removing an auger shear pin is 'fun'.....
It is a good idea though to spray or coat the bolts/nuts/connections with oil or grease, once in awhile.

Not rust on the shear bolts - rust in between the shaft ends where the shear bolt is attached. My point was that having a shear bolt does not eliminate the need to inspect/service the coupling; of course, with a shear bolt this is probably less of an issue. However, one can easily imagine years passing on a shear bolt coupling with rust slowly forming on the mating surfaces resulting in a much higher required break force.

 

[Elliott in GA]

Good point -- but one difference between clutches and shear bolts is that shear bolt connections can be greased.

I imagine that shafts running through sleeves (eg: snowblower augers) are more susceptible than mating flange connections (eg: PTO shafts), just because of the vastly increased surface area. But then, they are more likely to have grease zerks too, so it may be a wash.

Agreed - the point was that shear bolt couplings require some (although much less) attention/servicing too.