No, your nut isn't your problem ! When you slide your stump jumper down onto the gear boxes shaft the gear boxes shaft and the stump jumper has cut splines on the shaft and inside the hole of the stump jumper and they slide into each other like gears ! When the stump jumper slides on the shaft it will be really snug. The two will lock into each other so the rotary cutters shaft will turn the stump jumpers blades. If the stump jumper is wobbling when it's all the way down onto the shaft and that's the original gearbox and stump jumper then either the splines on either the gear boxes shaft or the splines up inside the stump jumper are stripped out and if the splines are stripped out then their both probably stripped out and need to be replaced. Another option is the stump jumpers machined lug that was machined to slide onto the gear boxes splined shaft has broken loose and that's letting the domed housing wobble. If that's the problem the that needs to be welded back in place or replaced then rewarded in place. You can add spacer washers to get the right cotter pin lineup through the castle nut and shaft but I guarantee you that's not the wobbling problem ! All that castle nut does is keep the stump jumper from sliding off the brush cutters splined shaft. When you slide the two together even without the castle nut they are supposed too be really snug together with no wobble at all ! You could actually torque the castle nut down 100 ft. lbs. and if the cotter pin holes didn't line up then back of the nut where you need to and even add a washer if needed. The castle nut isn't there to stop and wobbling , just to keep the stump jumper from sliding off the shaft. All your supposed to have to do is slide the stump jumper with the blades on it down onto to gear boxes shaft making sure it's all the way down in place. Then screw the castle nut down against the stump jumper not even torquing the nut down just snug it down until the holes lineup. Another problem that can cause the vibration / wobble is you might have bearings on the bottom side of your gear box and they are falling out

Yep on aircraft we are told to add or remove washers to get the holes to align with correct torque on nut. Also turn the cotter pin 90 degrees and turn end over bolt so key will not vibrate and fail.

I have added washers or made my owns washers or shims in the past so the the cotter pin properly engages the castle nut. I have found that if the castle nut is too "deep" on the threads, the cotter pin is more vulnerable and gets damaged and disappears easier. It happens fairly frequently that the cotter pins get broken and come out due to something hitting them during normal operations. Checking for the presence of the cotter pin and tightness of the stump jumper / blade carrier is part of my daily check.

Glad it worked!

spacers or rather shims is what needs to happen. the issue with the gear box noise is the fact that the gear mesh was not properly set up with shims inside the gear box. this would have shortened the shaft where the stump jumper seats and you may not need a washer. gear mesh inside the box is very important and that is where the noise comes from. the shims inside is what sets the length of that shaft. ask me how I know this lol ha ha.

Thank you for this. Mine is also vibrating pretty bad. This winter I think it will need a bit of work.

I am not a mechanic but I think you replaced a washer that was left out when the rebuilt your gear box. Just the fact that the castle nut did not go high enough to be secured with a carter pin would indicate that.

hi!

The "humming sound" since the rebuild is because the gear spacing in the gearbox is incorrect and too loose. The backlash should have been adjusted when they rebuilt it for you. Will result in premature failure of the gears.

Those groves in the castle are called crenelations.

The shimming that you did should be perfectly acceptable. We do it on aircraft all the time per the manuals.

That's just basic maintenance. Any time you bushhog that vibration can start from hitting something like a rock small trees to hitting the ground too deep. Just protect the seal. Always check the gear oil. That roar you hear could be low of gear oil. Or the sound of gears itself. Some to sound that way. Adding a washer or two to fill up space is common. When you had it rebuilt they could of missed putting that washer on to start with. Yes, that happens as well. I have seen some put a large lock washer there as well. You could put a bigger size cotter pin in to fill the space inside the hole. Take a hammer and form it around the nut. Don't leave any of it flopping. Pliers to spread the pin and a hammer to form it around the nut. Just a better fit. When working on old equipment it's just common. The way they build new equipment now with thin metal. I'd rather have the old. And fix it myself. I'm NO mechanical engineer by No means. I'm just a man with a tractor that likes to take care of his equipment. I've been doing this ever since I was a kid working on my dads equipment. If you allow it to fail because of bad maintenance. Your the only one to blame. It takes time but, well worth it in the end. Just watch what you hit with it. Check it from time to time. Even after you cut with it.

Your gonna have to get in to that gear box next year brother and replace that bottom bearing ! ! ifn ya got to put 2 washers in it time !

🔥 it with the torch stump jumper it's a taperd fit

Should have had a washer like that in the first place. Also, if they're tapered bearings, it should tightened to a torque figure then backed off until you can get a pin in, at least that's how I was taught and have always done that style of bearing. Just frapping it up with an impact wrench can put too much pre-load on the bearings, which usually wipes them out a lot sooner.

Could be gear mesh like other have mentioned but it also kind of sounds like straight cut gears like used in high performance applications(aka 1/4 mile cars)

If I could add my 2 cents of knowledge by the sound of the gear box I’d say who ever rebuilt this unit didn’t put enough shims on the rotor shaft to space the gears in the housing the specified mesh clearance and this is why the castle nut is threading on too far and you had to put a washer on under the castle nut , so you need to have the gear shims properly gaged that is why it is making the strange sound you hear if not the gears will mesh them selves to metal pulp. Do not continue to run this rotary mower until properly adjusted or $$$$. Sorry I guess that’s $2.00 worth of brain cells.Good Luck from Canada cheers !

Never had a problem with my brush cutter until I got a new tractor with automatic transmission. The PTO is started with a pull switch, like a riding mower, so even if you throttle down all the way, the brush cutter is going to start with a bang. There's no clutch to let out gently and start gradually. 9 times out of 10, when I throttle up I've got a vibration that's impossible to deal with. I hate it so much I'm using a finish mower to do most of my heavier cutting.

Way too much slack in shaft and hub Mine is extremely tight and I had to build a home made puller and grade 8 all tread screw

Wish I knew some company that could get parts for all the different brands of gear boxes Any suggestions????😊 Thanks 🙏

The humming is the gears not being alinement right. They sound way to tight. They are shimmed just like the gears in a truck rearend.

Sounds like either bearing is loose or damaged...

that gearbox does not sound good I put a new one on mine it,s very smooth.

Should be a taper press fit.stump jumper to shaft..i think your not torquing it enough.

Why not just drill a new pin hole? all it does is keep the castle nut from backing off

No, your nut isn't your problem ! When you slide your stump jumper down onto the gear boxes shaft the gear boxes shaft and the stump jumper has cut splines on the shaft and inside the hole of the stump jumper and they slide into each other like gears ! When the stump jumper slides on the shaft it will be really snug. The two will lock into each other so the rotary cutters shaft will turn the stump jumpers blades. If the stump jumper is wobbling when it's all the way down onto the shaft and that's the original gearbox and stump jumper then either the splines on either the gear boxes shaft or the splines up inside the stump jumper are stripped out and if the splines are stripped out then their both probably stripped out and need to be replaced. Another option is the stump jumpers machined lug that was machined to slide onto the gear boxes splined shaft has broken loose and that's letting the domed housing wobble. If that's the problem the that needs to be welded back in place or replaced then rewarded in place. You can add spacer washers to get the right cotter pin lineup through the castle nut and shaft but I guarantee you that's not the wobbling problem ! All that castle nut does is keep the stump jumper from sliding off the brush cutters splined shaft. When you slide the two together even without the castle nut they are supposed too be really snug together with no wobble at all ! You could actually torque the castle nut down 100 ft. lbs. and if the cotter pin holes didn't line up then back of the nut where you need to and even add a washer if needed. The castle nut isn't there to stop and wobbling , just to keep the stump jumper from sliding off the shaft. All your supposed to have to do is slide the stump jumper with the blades on it down onto to gear boxes shaft making sure it's all the way down in place. Then screw the castle nut down against the stump jumper not even torquing the nut down just snug it down until the holes lineup. Another problem that can cause the vibration / wobble is you might have bearings on the bottom side of your gear box and they are falling out.