A few (probably) dumb questions.

[RjCorazza]

can you possibly explain this a bit more? I just heard about the shaft length issue the other day (and how it's likely you need to trim shafts)? I can probably assume this one is ok since it was installed by dealer? how can you typically get them sized right? how do you cut them?

@dodge man explained it well. DO NOT count on the dealer correctly sizing the shaft. There are threads here, and videos on YouTube that explain how to measure and cut the shaft.
Definitely a measure twice cut once procedure!

 

[Jstpssng]

Just my two cents although neither will answer your question;

Cent 1- there is no such thing as a dumb question if you need to know the answer.

Cent 2- There likely are 10 or more relatively new tractor owners who read this and said "I am glad that he asked this!"

 

[dougtrr2]

The risk of damage is too great to assume the dealer supplied shaft is the correct length. It is pretty easy too figure it out. Unhook the shaft from one end. Collapse it as far as it will go. Make marks on the shaft or the safety cover. Reconnect the shaft. SLOWLY raise the three point watching the marks. Make sure they never get back to the collapsed length. If they do, STOP. You will need to shorten the shaft.

Doug in SW IA

 

[ericm979]

If the external PTO shaft is too long it will bottom out when the top link is shortened, and that can damage the bearings on the PTO shaft inside the tractor. The hydraulic top link may be able to go shorter than the turn buckle type, and you're much more likely to do it. So you'll need to check all the PTO shafts on your implements when you get the top and tilt.

To shorten a PTO shaft you pull the two halves apart and cut each side with a hacksaw. I prefer to take the outer plastic shield off and cut it separately. There's instructions all over the web. The manual for many implements also has instructions as do the documentation for the shaft itself.

I do a lot of backing into thick brush with a rotary cutter. To avoid damage, first go slow. If you back it into something solid like a stump you don't want a lot of momentum. I have a hand on the 3pt lift control so I can lift the mower away from anything bad like a large rock that the mower's pulled out of the ground. Ideally you will have examined the area for obstacles before mowing it but that's not always possible.

 

[CoyPatton]

You are wise to be concerned and to ask!
Assuming you did not go with the economy model brush cutter and it is appropriately sized for your tractor’s size and HP, damage to your 3PH or brush cutter is minimal in my opinion.
Others have addressed the issues related to too long a PTO shaft. There are issues related to too short as well. One I have not seen is when extended the shaft will slip apart, but also if it does not have sufficient overlap you can damage the shaft.
My recommendation is to learn all you can prior to cutting. Measure 2x or more before cutting.
One caution. I had to replace a shaft, not because it was mis- cut, but because after cutting I added a QH. It was a short shaft to begin and may not have been long enough as supplied for the QH. But I had to replace it to use the QH.

 

[rgr33]

Things to watch for on your first attempt at brush cutting

any unusual sounds or violent shaking of the mower as you work the implement

any unknown objects that are hidden in the thick brush, rocks, old fence posts, stumps, etc

any deep holes that your wheel could sink into and cause mayhem

other than that, and if you follow the good advice already given here, you should make short work of that mess

 

[UncleW]

Bent up the dealer installed PTO shaft on the 3 pt cause it was cut too short

I mowed my neighbors vineyard which got overgrown with 1” elm saplings and a bunch of brush. Medium duty 5’ brush hog was fine as long as I kept it in 1 st gear. Made 2 passes at different heights

Did have trouble at the end of a couple of the rows where the end turnaround was too tight up against a rocky bank. Got it stuck on a boulder at 0 mph and sheared off a hitch pin in the stabilizer for the 3pt linkage before anything else broke. Replaced 2 stabilizer hitch pins with low strength ones a size down. Thought was they would act like shear bolts and protect the 3 point. They did. And you could hear it snap cause the mower wasn’t running

Obvious downside of damaging something if one breaks while you’re mowing. They didn’t but I was darn careful

 

[Trackerjoe]

can you possibly explain this a bit more? I just heard about the shaft length issue the other day (and how it's likely you need to trim shafts)? I can probably assume this one is ok since it was installed by dealer? how can you typically get them sized right? how do you cut them?

YouTube has many good vids on cutting shafts. It's easier than it sounds. Tractor Mike's channel is usually a good place to start.

 

[5030]

Hasn't been directly mentioned, so I'll add that an improperly sized pto shaft can do SIGNIFICANT damage to the tractor if it's too long and bottoms out.

Follow the pto shaft cutting directions that are in the operators manual. Easy-peasy.

 

[EddinKY]

Just be aware that those saplings you are cutting off 6" tall turn into spears as they dry out...they like to pierce tires.