Chasing down a vibration in Woods brush mower

[MESSMAKER]

My 3 year old Brushbull has picked up a good bit of vibration as the RPMs go up. I have checked the PTO shaft and blades and they seem OK. I found that one of the bolts holding down the gearbox was not tight, but I took care of that. I suspected that Maybe I bent an output shaft. I have run cutters for decades and never had this happen. I have watched the rotation of the blades but I am not sure I can trust my eyes. Anyone have any ideas?

 

[Midniteoyl]

Output shaft bearings?

Home

Shop Parts Online

store.germanbliss.com

 

[rademamj1]

Mine (BB60.50) only incured vibrations after the blades hit serious metal debris mowing along side the Interstate, and slightly bent a blade. It was just a minor deformation, barely noticeable, but at 15,000 rpm, it was enough to create vibrations. I ordered both new blades and bearings from German Bliss, but the blade replacement eliminated the vibrations. I now have a set of backup bearings just in case.

 

[RickB]

15000 rpm? Must be one of those high speed BB's.

 

[Tinhack]

Yeah, that thing must sound like a jet engine. 15,000 rpm!

 

[rademamj1]

Yikes....your right. In the cutter specs, its 15,000 fpm on the blade, not the rpm.

 

[beckmurph]

On my BB48x the welds that connected the crossbar to the blade pan broke.

Replaced the blade pan and cured my vibration.

 

[MESSMAKER]

I guess it could be the blade pan. It is dented but in one piece.
New blades are $175. What is the cost on the blade pan?

 

[beckmurph]

I don’t remember the cost exactly, but it was around $200

I have replaced 2 blades because they broke. Rocks, stumps, logs and other things I have hit with this cutter.

But, the condition of the blades have not caused any vibrations.

Loose gear box and broken welds on the blade have caused vibrations.

 

[3gunr]

Make sure your blades are swinging freely. If mine bottom out or get any grass in between the pan and blades it will shake like crazy. I usually sray some lube up there and swing them by hand to loosen them up. This has happened on al 3 of my cutters over the yrs.

 

[Slowpoke Slim]

Make sure your blades are swinging freely. If mine bottom out or get any grass in between the pan and blades it will shake like crazy. I usually sray some lube up there and swing them by hand to loosen them up. This has happened on al 3 of my cutters over the yrs.

This is about the only time mine shakes. When I hit something that causes the blades to swing out of line. Then it shakes like mad too, until I stop it and restart it (the pto) again. Most of the time stopping and restarting the mower (pto) takes care of it. Once in a while I have to shut it off, raise the mower and swing the blade back to straight by hand.

 

[MESSMAKER]

This is about the only time mine shakes. When I hit something that causes the blades to swing out of line. Then it shakes like mad too, until I stop it and restart it (the pto) again. Most of the time stopping and restarting the mower (pto) takes care of it. Once in a while I have to shut it off, raise the mower and swing the blade back to straight by hand.

Maybe this is it. I tried to take a putty knife and some WD40 to clear them.It seemed to help but not cure the problem. I might try removing the blades and making sure there is not some debris still giving me problems. Good thing it's a Woods. Not a big deal.

 

[rdewey]

Like already mentioned. Make sure your blades pivot freely. If they are stuck it will shake like crazy. Next make sure your blades are not excessively worn. Blades must be the same weight. A bent gear box shaft is very unlikely. There isn't hardly enough weight in your cutter to bend the shaft. A bent stump jumper is possible. Does your unit have a round or football shaped stump jumper?

 

[MESSMAKER]

Like already mentioned. Make sure your blades pivot freely. If they are stuck it will shake like crazy. Next make sure your blades are not excessively worn. Blades must be the same weight. A bent gear box shaft is very unlikely. There isn't hardly enough weight in your cutter to bend the shaft. A bent stump jumper is possible. Does your unit have a round or football shaped stump jumper?

It has the football shaped one. It has a dent on it ,but I don't see it causing a vibration. It may be what I am cutting getting wrapped around the pivot on the blades because the vibration seems to come and go to some degree.

 

[Midniteoyl]

because the vibration seems to come and go to some degree.

Vibration is going into and out of resonance.

 

[beenthere]

Mine (BB60.50) only incured vibrations after the blades hit serious metal debris mowing along side the Interstate, and slightly bent a blade. It was just a minor deformation, barely noticeable, but at 15,000 rpm, it was enough to create vibrations. I ordered both new blades and bearings from German Bliss, but the blade replacement eliminated the vibrations. I now have a set of backup bearings just in case.

Blade tip speed is 15,525 feet per minute, according to specs and likely that is at PTO speed of 450 rpm.

 

[akajun]

I had this pop up on a old bushog I had, had trouble pinpointing it. Took of the stumpjumper to look for a crack and the stumpjummer had a weight welded to one side that went missing, I could see where it was tacked to.
I simply took the blades off, put the jumper on a lawn mower blade balancer, and played around with scrap pieces of steel at different spots till it was level and welded them in place, then installed the blades and double checked. Ran smooth after that.

 

[MESSMAKER]

Put new blades on it. Vibration went away. The old ones looked just fine. Sometimes, you never know.

 

[Baby Grand]

Same with my 13 year old Brush Bull. If I hit a stump or rock it sometimes causes one or both blades to swing off the cross bar centerline. The blade pivot joints are stiff and require some force to get them back into alignment. Usually spinning it up, unloaded, is enough to staighten them out. A few times i had to shut down, raise the cutter and yank on a blade to ftee it up. Debris - shredded sapling or vine bits - may be the culprit. Sometimes smearing some oil, grease or anti-seize on the area around the pivots helps.

 

[workinonit]

450 RPM? Interesting.