Pond Boss Forums INTRO Questions & Observations Bush hog recommendations?

You have already been given some good advice. I'll add what I can.

Slip clutch or shear pin - it depends.

If you have a tractor on the mower that is on the bigger side for the size of the mower then a slip clutch will prevent a lot of frustration of replacing shear pins. But as has been said, for the slip clutch to work it needs to be loosened up, slipped, and re torqued to make sure it does not "freeze up". This should be done at minimum at the beginning of each mowing season. If it freezes up, you have no protection for the drive line or the gear box. We have three 15' flex wing mowers that all have slip clutches on each of the three gearboxes that have blades attached. We mow road ditches around our farm fields so they are no stranger to hitting dirt and who knows what. Those mowers work the best on 100-125 hp tractors. At one time I did not have any tractors in that range and instead used 160 hp tractors. The problem with having a tractor that is larger than the mower needs to do its job is that you can get in heavy grass or hit the dirt and before the tractor starts to grunt letting you know you are loading the mower too heavy there will be smoke rolling from one of the slip clutches. Slip one for about 15 seconds and the torque bolts/nut will need to be adjusted. If it is not, the clutch will slip to easily the next time. Slip it excessive about three or four times and you need to put new friction disks in the clutch assembly. I have found if we do not put too big of tractor on the mowers, the engine will lug down before the clutch slips making for a lot happier operator and less down time. They will still slip if one rotor hits something too solid, but the operator has warning by the engine pulling down.

Big mowers doing heavy duty work need slip clutches. Small mowers doing heavy duty work (clearing trees, etc.) need slip clutches.

Having said all that, my 5' JD mower on my play toy JD3038E has a shear pin and I would not have it any other way. I think the mower has either a 40 or 50hp rated gear box. The tractor is 38 engine and probably around 36 pto hp. I have never sheared a pin. As long as the tractor is sized a little lower than what the mower gearbox and drive line is maximum designed for the shear pin system has the advantage of not having to worry about freeing up the slip clutch every season. If I had a 50 hp tractor on this mower, I would likely want a slip clutch because when I hit something tough I would be shearing pins and be unhappy. But with the size tractor I have, even if I hit the dirt or get in super heavy fescue it just pulls the engine down rather than shearing the pin. A 50 hp tractor would shear the pin.

So for average consumer type mowing with a mower that is rated a little heavier that what the tractor power is I like a shear pin system just fine. On the other hand a slip clutch would also be fine if the tractor was of rated power less than the gearbox and driveline, because even if it froze up the tractor likely could not damage the drive line or gear box. A slip clutch or shear pin is as much for protecting the drive shaft as it is the gear box.

One thing that makes the slip clutches so poor and such short life if slipped is that they are made of the same stuff the new vehicle brakes are made of. In other words "not asbestos". Just like the brakes on new vehicles suck compared to the old days (that is all that black dust on the wheels) it is the same for the material in the slip clutches. It is just not as good as it used to be and freezes up worse than it used to.

Keeping the mower in a shed and out of the rain helps keep the slip clutch from freezing up but "helps" is the key word, not prevent. Left out in the elements they will freeze up worse.

That is what I think I know. But sometimes I'm mistaken. We have rebuilt a lot of slip clutches over the years.