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MAINTENANCE
FX17/FX21 02/11 Maintenance Section 5-11
© 2011 Alamo Group Inc.
MAINTENANCE
General Information on Flail Mower Vibration
FLAIL MOWERS
INFORMATION BULLETIN NO. 5
EXCESSIVE VIBRATION
Vibration is a MONSTER and if allowed to continue unchecked, can cause the complete break-up of a machine
in a very short time.
A properly operated Flail Mower will produce very little vibration. If vibration does occur, the mower should be
stopped and the trouble corrected, as warranty does not cover failures resulting from continued operation after
something happens to cause the mower to vibrate excessively.
Vibration is caused by a rotating part which is out of balance. This could be the cutter shaft or, on those models
having a universal slip joint assembly drive shaft, from the drive shaft.
If the two extreme ends of the drive shaft, (the splined yokes which fit on the tractor power take off shaft and on
the mower gear box driven shaft), are not parallel, vibration will be evident.
This is because of the mechanics of a universal drive wherein the rotational speed through a universal joint is
not uniform. If the ends of a universal drive shaft are parallel, the uneven rotation effect is cancelled out and the
machine being driven will be driven at a uniform rate of speed. However, if the ends are not parallel, the
uneven rotation effect may be multiplied, resulting in a speeding up and slowing down of the entire mower
system (gear box, extension shaft, pulleys, belt, and cutter shaft) each revolution. This effect can be readily
noticed if the mower, while running, is raised to an extreme height on the tractor lift.
For smoothest operation, the tilt of the mower should be adjusted (on a 3-point hitch, by adjusting the length of
the top link between the tractor and the mower) so that the ends of the drive shaft are parallel when the mower
is down in operating position. Raising the mower, while running, to extreme heights on the lift should be
avoided.
To check where the vibration is originating, first be sure the ends of the universal drive shaft are parallel. Then,
if vibration is still present, remove the drive belt and run the mower. If vibration is still present, it most likely is
coming from and caused by a bent drive shaft. If so, the shaft should be replaced or straightened. If the
vibration is gone - the drive portion of the mower is running smoothly - then the vibration is probably coming
from the cutter shaft (it could be a pulley out of balance or a faulty belt with a varying cross section, but this is
not likely).
The cutter shaft will run out of balance if:
1. Wire, rope, string, rags, etc., around the cutter shaft,
are holding the knives in a folded back position.
Remove such foreign objects and be sure all knives are free to swing to the extended position.
2. (a) Knives are missing or broken.
Replace missing or broken knives.
(b) Knife hanger lugs are broken off shaft.
This condition usually results from continued operation in contact
with large hard objects where the knife hanger lugs themselves are hitting the hard objects. Lugs should be
replaced using arc welding equipment so as not to direct too much heat in one area of the shaft.
3. Cutter shaft ball bearings are worn
enough to have radial “play” in them. Replace ball bearing and other
worn parts to eliminate "play".
4. Shaft is bent.
The shafts are straight within a couple of thousandths of an inch when they are made. It is
possible that they will become bent in use, such as if the shaft is hooked on a stump while the tractor is moving
forward at a good speed.
5. Shafts are operated at improper speed.
Rotating shafts have what is known as a natural period of vibration.
The same is true of the cutter shafts on the Flail Mowers.