Bush hog shear pin vs clutch

[Catfish Man]

Which do you prefer?
Pro's and cons?

assume 45 hp tractor

I have my preferences, I just want to see what everybody else's thought process is, and make sure I'm not overlooking something.

 

[greg_g]

It been my experience that the shear pin versus slip clutch decision has less to do with the hp of the tractor than it does with the size and duty cycle of the cutter (cutting swath and light/medium/heavy duty). The purpose of both the shear bolt and the slip clutch is (#1) to prevent potentially damaging shock loads from reaching the tractor, and (#2) minimize damage to the cutter. It goes to the economics of repair. That, plus the fact that a shear bolt is useless on a splined shaft.

A general rule of thumb is slip clutch on six foot and above, shear bolt on five foot and below. But there are exceptions. In the case of smaller cutters, there are folks that pay extra for heavy duty models - usually cuz they expect to subject the mower to rough conditions. That's an argument for a slip clutch. In the case of the larger cutters, there are some folks that don't expect ANY medium/heavy duty cutting, and just want a larger mower so they can get done faster. Those folks can often get by with shear bolt protection.

//greg//

 

[Bigfoot62]

Greg gave you some great information.

I would just add, if you don't take care of a slip clutch, you might as well not have one.

By this, I mean:
At the beginning of each mowing season, you have to loosen the tension bolts on the clutch, lube it, and make it slip. Then, re-tighten the bolts back to where they were. (just count the exposed threads or measure before loosening)

If you're wondering how I know this . . .
Let's just say, BTDT.

 

[Hollow]

Personally I wouldn't buy/have a rotary cutter without a clutch. I keep mine looser than normal to allow it to absorb shock when the blades contact something solid. Clutch discs are much cheaper than a gearbox or tearing a tractors busted PTO apart. Plus if it does hit something all you have to do is lift the mower and the clutch resets (its good to idle the tractor down and let the clutch reset faster) and you keep going. With a pin you'll have to stop, shut the tractor down, get your tools out, fix it, put everything back up then get everything going again...

 

[jenkinsph]

Greg gave you some great information.

I would just add, if you don't take care of a slip clutch, you might as well not have one.

By this, I mean:
At the beginning of each mowing season, you have to loosen the tension bolts on the clutch, lube it, and make it slip. Then, re-tighten the bolts back to where they were. (just count the exposed threads or measure before loosening)

If you're wondering how I know this . . .
Let's just say, BTDT.

I have the clutch model but agree with making sure it is adjusted each time it sits for a long period. For some people who have alot on their plate this may make the shear pin a viable option as it is more forgiving.

 

[Rockgod]

If all you'll be mowing is light grass then a shear pin might be the way to go. Anthing else would be a slip clutch. :thumbsup:

 

[nelsond7004]

Personally, I would go for the slip clutch. As Bigfoot62 points out there is some maintenance involved with slip clutches. From what I know, moisture can cause a clutch to seize even sitting in the barn.

I have heard of some people buying a standard shear bolt protected cutter and then adding a slip clutch. Some claim they have a fail safe by having a shear bolt holding the clutch on. That way if the clutch failed, you might have a chance that the bolt would shear. I would imagine you might have to step up the shear pin to a grade 3 bolt. Just a thought.

 

[johnrex62]

I feel more comfortable with a shear pin because I am bad about the pre-flight checklist. I tend to check my oil and fluids at semi-regular intervals, but not before every startup.

I am sure there will be a time that I let my clutch maintenance routine go a little longer between executions than I should and could put myself at more risk than necessary.

I have been running a shear pin on my Mowhawk cutter with very minimal inconvenience. It has sheared only once, the day I got it and strangely when i was backup up over a collection of cut grass which was balled up. Since then I have cut large groups of 2-3" saplings and 4 foot tall grass with no bogs, slow downs or broken pins. The only reason I can think of for the first pin break is my inexperience may have let me run the engine too slow or something. Otherwise, the shear pin performance has been outstanding with no need for maintenance.

Sure, it will be more work (about 5 minutes to find the wrench and replace the pin) when it does shear, the peace of mind that it is working properly is worth that to me given my inattention to infrequent maintenance tasks.

 

[SPYDERLK]

Greg gave you some great information.

I would just add, if you don't take care of a slip clutch, you might as well not have one.

By this, I mean:
At the beginning of each mowing season, you have to loosen the tension bolts on the clutch, lube it, and make it slip. Then, re-tighten the bolts back to where they were. (just count the exposed threads or measure before loosening)

If you're wondering how I know this . . .
Let's just say, BTDT.

How do you know that? Did you twist a telescoping PTO shaft or damage a gearbox. Im curious to know because in 50 yrs the only thing Iv ever had to do to a slip clutch is grease the fitting and tighten it when it starts slipping. Seems like Iv adjusted/tightened about 6 times over that period. Last time was 2yrs ago as i recall.
larry

 

[greg_g]

How do you know that?

I can't answer for BigFoot, but I can tell when I'm in stuff that should be making the clutch slip. If it doesn't, then there's something wrong with my maintenance plan.

But if you have had the same slip clutch for 50 years, then it certainly wasn't made in India or China. That's pretty much the junk we have to contend with today. The friction discs and pressure plates literally freeze together during periods of inactivity. I'm almost certain the cause is exposure to moisture, something that most owners who don't keep their equipment in climate controlled storage can avoid.

So periodically we must back of on the tension and break the discs and plates apart. Often it just takes a little intentional slippage to clean the surfaces. But I've on occasion had to disassemble/clean/resurface/reassemble. I want to be confident that it's going to slip at the appropriate time, so I try to get out ahead of the problem by doing my own twice a year; spring before starting the summer work, and fall before putting them into winter storage.

//greg//