Front wheel shimmy

[Bryan Edwards53]

I have a Bad Boy 72" ride on and for some reason the front wheels shimmy quite badly when it gets up to speed. The left wheel is noticeably worse than the front. Is this a normal thing or is it indicative of somrthing out of ali8gnment or balance?

 

[jmurray01]

Sounds like the wheel bearing. How old is the mower, and how many hours are on it ?

 

[KennyV]

I have a Bad Boy 72" ride on and for some reason the front wheels shimmy quite badly when it gets up to speed. The left wheel is noticeably worse than the front. Is this a normal thing or is it indicative of somrthing out of ali8gnment or balance?

I think you mean the left front is worse than the right front... The gauge wheel yolks and forks may not be perfectly formed, swap them left to right and see if the problem moves...
Also because of the torque needed to rotate the blades, one side of the deck will lift & be lighter than the other... the light one will not track as well as the side of the deck that has more weight... :smile:KennyV

 

[jmurray01]

I think you mean the left front is worse than the right front... The gauge wheel yolks and forks may not be perfectly formed, swap them left to right and see if the problem moves...
Also because of the torque needed to rotate the blades, one side of the deck will lift & be lighter than the other... the light one will not track as well as the side of the deck that has more weight... :smile:KennyV

I did not know that Kenny! How does that work exactly ?

 

[KennyV]

It is very apparent with a shaft drive into a right angle gear box... the larger the cutting width the more it will pick up one side...
Using an industrial Hustler with bat wing (Range wing) decks driven from the front deck, you have to set up the front deck height for the torque lift, but your turning all 12 feet width of finish mower decks with the One front PTO shaft...
I'll try to get some pictures of it doing it.. :smile:KennyV

 

[jmurray01]

It is very apparent with a shaft drive into a right angle gear box... the larger the cutting width the more it will pick up one side...
Using an industrial Hustler with bat wing (Range wing) decks driven from the front deck, you have to set up the front deck height for the torque lift, but your turning all 12 feet width of finish mower decks with the One front PTO shaft...
I'll try to get some pictures of it doing it.. :smile:KennyV

Ah I understand now.

 

[benski]

It hadn't ocurred to me until Kenny ponted it out, but it makes sense. Similar physics as the torque reaction on shaft drive motorcycles, eh?:smile:

 

[Bryan Edwards53]

Thanks for the replies

No definitely not the wheel bearing as it has just had a new wheel fitted and new bearings. The old wheel completly collapsed early this week. I think that was likely because of it being subject to the forces caused by the shimmying over a period of time.

It does it with or without the blades engaged so guess that rule out the torque factor as well

I have just been looking at it and it does seem that the problem wheel sits more lightly than the other but I cant see any reason why that would be.

I am going to taker it up to the dealer and see if they can dampen it down some how.

 

[GentlemanFahmah]

In my experience, gauge wheels shimmy at speed when all the components of the vertical shaft are worn such that it allows the wheel to track at a slightly tipped forward angle. Check the bearings and races in those vertical shafts for wear and grease; I'll bet the bearings are gummed up and dry and have worn such that they now have enough slop in them to allow the front wheels to go into the death wobble at speed. Keep on the grease gun on all those parts and particularly so if you are washing the machine down after each use which allows minute dust and sand particles to wick down in the bearings and shafts.

These wheels are "trailing wheels"; the axle of the front wheel is behind the vertical centerline of the pivot shaft. If the alignment bushings on the top or bottom of the vertical pivot shaft are worn, then they will allow the gauge wheel pivot shaft to tip forward when traveling at speed and setup the wobble - particularly so on pavement or hard flat surface.

Here's a schematic showing the parts and numbers I'm referring to: http://www.wctractor.com/outdoors/PARTS/2006/AOS%20Pages/front%20wheel.pdf.

 

[oldyellr]

This is similar to when you get a shopping cart where one front wheel oscillates wildly. Other than wear, it's because the axis has been bent out of vertical, or wherever it's supposed to be. Just a degree will make a difference, even though it's not apparent to the eye.