Bush hog blade stopping

[yanmars]

I was mowing grass with a 5 foot light duty King Kutter brush hog using a 40 horsepower NH tractor. It cut well in areas I had cut earlier this Spring but when it got into 2 foot tall grass (not that thick) it caused the blade to nearly stop but enough it did not cut at all. The mower has always been greased, the shear bolt was not damaged or broken. The blades are dull. When I would get back to the prior cut grass the blades would pick up speed and cut again but it had nothing for the taller grass. The tractor was moving at slow speed with engine RPM near 2500.
The problem is most of the grass is tall as my main tractor and mower have been down for 3 months waiting for an odd sized O ring. Really need to mow the tall stuff with what I have. Any thoughts or suggestions?

 

[airbiscuit]

Not sure this will help, but if you adjust the rear tail wheel so the rear of the mower is elevated, the mowed grass can more easily exit the mower. It can make a difference in the power needed to spin the blades.

 

[Williy]

Can you raise the brushhog then cut and then lower it
and keep making passes till you get it cut
and blades not sharp don't help it just makes it harder
to cut and takes a lot more power to bull threw

willy

 

[Roadworthy]

The mower blades slow down. Got it. Does the tractor engine slow down as well? If the mower slows and the tractor engine does no slow you may have a slipping clutch.

 

[yanmars]

It is a hydrostatic transmission. The engine does not bog down, just the bush hog.

 

[WranglerX]

Is there a clutch on the mower PTO shaft? ....Something similar to image below...

 

[pjbci]

If blades are slowing down but not the engine. Something is slipping. The clutch pictured above or the clutch inside tractor.

Rare but possible with some rotary mowers, the output shaft on the gearbox has sheared the key but continues to spin from friction of a tapered shaft and tight bolt.

 

[yanmars]

No slip clutch on the mower and the shear bolt is not broken. Hydrostatic drive on the tractor.

 

[Tx Jim]

Sounds typical for pto clutch slipping. Hyd engaged pto clutches normally have a test port to check hyd pressure. I suggest to check pto clutch pressure.

 

[Roadworthy]

I don't know how your tractor's built but my Kubota is HST AND has a clutch. When the clutch is depressed it disengages the PTO and my mower slows down. I suspect if that clutch was slipping the mower could slow down in use. Even with HST you can have a defective clutch.

 

[CobyRupert]

Can you see the pto shaft (on the tractor side of any shear bolt) slow down when the blades slow down? This means the pto is probably slipping inside the tractor.

If the tractor’s pto shaft rpm stays consistent with the tractor engine’s rpm but the blades slow down, the slippage is elsewhere on the mower. Some shear bolts can be broke and look okay if the sheared head doesn’t fly out.

Like roadworthy says, check adjustment of pto clutch.

 

[LD1]

Can you see the pto shaft (on the tractor side of any shear bolt) slow down when the blades slow down? This means the pto is probably slipping inside the tractor.

^^^THIS

Basic troubleshooting.

The engine (indirectly through clutches and gears) drive the blades on the mower.

The only parts visible are
1. RPM's via the tach
2. The PTO shaft
3. The blades on the mower

Since 1. RPM's are not slowing, but 3. The blades are.....then you obviously have something slipping in between.

But what about #2. What is the PTO shaft doing? That alone will tell you if the issue is something on the tractor side, or on the mower side.

 

[Thomas]

Have you try mowing when grass good and dry?...it will give easy and better looking cut.

 

[yanmars]

The grass was dry. The tractor RPMs do not drop but the blade and the PTO shaft both slow and nearly stop. The New Holland does not have a foot clutch on the hydro trans. Will try to check more in the future. Thanks

 

[MESSMAKER]

Check your hydro fluid.

 

[yanmars]

I will but I am pretty sure I had it full a week or so ago.

 

[airbiscuit]

I've had shear pins break, with ends remaining intact giving the appearance that all is well. You've checked that, so the problem sounds like issues with the PTO clutch.

 

[LD1]

The grass was dry. The tractor RPMs do not drop but the blade and the PTO shaft both slow and nearly stop. The New Holland does not have a foot clutch on the hydro trans. Will try to check more in the future. Thanks

That's not good news. If the pto is slowing and the tractor is not....the clutch that drives the pto (inside the transmission/rear axle of the tractor) is slipping pretty bad.

 

[LD1]

How many hours and what's the age of this machine that a light duty kk 5' mower is slipping the internal clutch of a 40hp machine?

 

[yanmars]

The tractor has about 1850 hours on it, I would guess it is 20 years old or so. Never heavily used by me (us) but lent out and the guy abused it badly but i did not think he did any PTO work but bent the bucket and did other damage that was repaired.