Senile Texas Aggie - comic relief for the rest of you

One of the mistakes I often see people do with 3pt pto driven rotary mowers is not having them adjusted right regarding height..both height off the ground and height looking front of mower to the rear of the mower. For light easy cutting, it's usually not an issue, but in thick high forage it can make a big difference.

Normally, the front and rear of the mower (A TO B) should be level with each other, with 1/2 the weight of the mower on the lift arms and 1/2 the weight of the mower on the trailing wheel(s). But, in thick stuff, I find I can do better if the front is a little higher than the rear. This takes some cutting stress off the blades as they come around to the front of the mower, and then as the tractor moves forward and the blades make there cut across the rear of the mower, final cut height is made. You can adjust how low the trailing wheel drops and how much weight it bears by moving pins or bolts on the tail wheel bracket and by lengthening or shortening the center link.
Never, should the mower's skid plates (C) be constantly dragging the ground like you see in the drawing below..

You want to be carefull about stalling the pto shaft and applying power to a stalled mower........you will be popping shear pins soon, or worse:

(Yes, that's mine..hub on the ujoint that connects to a gearbox was rusted to the gearbox input shaft and the hub could not slip enough to shear the pin....it twisted and broke the driveline instead. It's from a 3Pt post hole auger, but I have seen the same thing happen on mowers)

90% of the time, stalling a mower is caused by excessive forward speed and a low PTO rpm combination.
Tractors today are rated and advertised by how much engine HP they have, but there is also a drawbar HP rating and a PTO HP rating. Of the 3, PTO HP is always the lesser.

Mr. @greybeard and others,

Thanks for the guidance on the use of the mower and regarding the PTO and its clutch. I am quite relieved to know that the PTO clutch is not damaged in some way. I feared that I had screwed it up somehow and faced a possibly large repair bill.

My shredder definitely looks like the drawing. I will adjust it so that the front of the shredder is a little higher than the rear, as I have the overgrown pastures to contend with.

Now, what's the best way to sharpen the blades on the shredder? Can I use a portable grinder on the blades while still on the mower, or will I need to remove the blades? If the latter, what will I need to remove the blades -- a HUGE socket with a 10 ft long breakover bar?

Senile Texas Aggie

I sharpen them with a 4" angle grinder, still on the unit, while it's on the tractor.
I move tractor to level ground, set the parking brake, lift the mower to the full height the 3pt will raise it, put blocking about 3/4 way back on each side of the mower, and let the mower down on the blocking, then shut the tractor off. Access is from the rear of the mower where the grass exits. I don't actually have to get under the mower with my body, just reach my arms under.
Takes less than 15 minutes.

You 'can' do it with the mower sitting on the ground, but it's hard to get the grinder in the right angle position.

under NO CIRCUMSTANCES would I (or you) you do it without the mower setting on something solid or just hanging off the 3pt lift OR with the tractor running!!

Some however, insist the ONLY safe way to do it is to
1. Take it in and let the service guy risk his neck sharpening them (because I guarantee, he's NOT going to go to the trouble of removing the blades just to sharpen them)
2. Remove the blades yourself and sharpen them.
3. Remove the mower from the tractor (actually, you would be removing the tractor from the mower) , turn the mower upside down with the front end loader and sharpen them while the mower is upside down and all the gearbox oil is leaking out the vent hole.

A good impact wrench and proper size socket will generally remove the nuts from the blade bolts, but I've seen some that did take a good 3/4 or 1" breakover and cheater pipe. Also saw a couple I had to cut the nuts off with oxy/acet torch and replace the bolts and nuts when done.

If you want to take the blades off (how long are they??) I'd use some PB Blaster, Fluid Film or other penetrating oil on the bolts and let it sit a while first. Wouldn't bother with a light oil like WD 40.

I have no choice but to take the blades off my GT mower, no way to get to the blades while they are installed. I hand sharpen them in a vice with flat files, don't have a grinder of any sort, would probably screw them up if I did unless there was some sort of rest to make sure I got the angle right. Have never seen the insides of a 3 PT rotary mower.

Bruce said:

GT mower

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What is a GT mower?

Bruce said:

Have never seen the insides of a 3 PT rotary mower.

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Now you have. This one looks like a 4' wide model.


PB Blaster/penetrating oil et al won't help much with properly torqued nuts of bush hog/rotary mower blades like the ones being talked about. It only helps with corrosion and sometimes with galling. These nuts are just plain TIGHT!

You don't see the nuts in the picture because they are on top of the blade stubs. The blade bolts, have a swage, a flat, or some other stamped/machined in area that locks the bolt to the stub so you don't need a 'backup' wrench under the mower. The stub, is almost always obscured from view by the stump jumper, which is the big dish shaped object in the center of my previous picture.


The nuts are generally accessed thru a hole in the mower deck.

Mr. @greybeard, sir! Thanks for the info on sharpening the blades. I will do that soon.

Senile Texas Aggie

greybeard said:

What is a GT mower?

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Garden Tractor! You know, the "wanna be" of tractors. Mine is 24 HP with a 54" 3 blade deck and a 50" snow blower. I think people with a 24 HP sub-compact tractor get a lot more capability for their HP. Of course they pay a lot more too.

greybeard said:

Now you have. This one looks like a 4' wide model.
View attachment 52551

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That doesn't look like something that is easy to take the blades off. I gather the ground edge faces down which is why you can get an angle grinder on it with the blades still on. What do you do to keep them from moving while you sharpen? I think I'd be tempted to lift it to perpendicular by the top link connection hole with the chain hooks on the FEL rather than doing it from below. Oh my aching back!

Bruce said:

What do you do to keep them from moving while you sharpen?

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No, ground edges are facing up, which is why you want to use a 4" angle grinder and not a 9" grinder.
The blades are heavy enough to usually stay right where you rotate them to.

If you hang one vertically, you will have to find some way to lock the input shaft of the gearbox, as the blades will then want to pivot pointing down...and in a hurry too. I tried it once........a real pita.

Believe me, it really is an easy and quick job to sharpen them on the mower, with the mower in a horizontal but blocked up position. I just did mine a couple weeks ago before mowing my neighbor's place. I sharpened his last week.
(I do recommend doing it on the grass or dirt tho...not on a cement floor.)

Blades aren't too bad to remove, depending how beat up the threads are.
Most manufacturers tho, strongly recommend replacing the bolts with new ones if you remove the blades for any reason. Those bolts take a real beating under there and no sense risking fatigue cracks result in a blade flying off. (I've only lost one blade in my life, and it was from the blade itself breaking right at the bolt hole.....you know it right away.the whole thing shakes from being so out of balance)

The center nut that holds blades/stumpjumper & everything to the gearbox output shaft is the one that can really make you pull your hair out.....then, you have to hope it all just slides off the tapered shaft and splines......

Bruce said:

Garden Tractor! You know, the "wanna be" of tractors. Mine is 24 HP with a 54" 3 blade deck and a 50" snow blower. I think people with a 24 HP sub-compact tractor get a lot more capability for their HP. Of course they pay a lot more too

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It's not all the garden tractor's 'fault' Bruce. Most of it has to do with how the mower deck drive is designed. You will never get the mechanical HP and torque from a belt driven mower you will from a pto driven deck that has a gearbox on it, with that heavy rotating mass underneath. Even garden/lawn tractors that do use a pto driven mower can't duplicate what you get from the heavy blades of a like sized mower such as what we are taking about. Inertia is a very powerful weapon against resistance from tall, thick grass. That mass acts just like a big flywheel, storing energy.