I destroyed the gearbox on my brush hog.... help

[Horse Family]

Hey All, First time posting on this forum.

I have a 1966 Ford 4500 Industrial Tractor with the 3 Cyl Diesel.

I bought a used howse 6 foot cutter, and have used it a couple times, probably cut about 6 acres with it total. I know the person who owned it previously and he seems to take good care of his stuff, but admittedly his pastures are like lawns, not much hard stuff to cut.

I noticed the gear box had gotten real loose and so I loctited all the bolts. Then I hit a small stump and broke my first shear pin. Also note, I had a oil leak from around the input shaft seal so i would add gear oil occasionally.

Anyway today my friend was helping me brush hog while i was doing other things and he said it started making a terrible noise. We parked it and opened up the gear box and this is what we found -

.

So obviously the gear box is toast. What I am trying to figure out is why did this happen, and how do I prevent it in the future. I don't want to buy a new gear box and have it get destroyed by the 3rd time I use it.

Looking at the model number of the gear box, it appears to be a 40HP rated gear box. Should i try to replace it with something heavier duty? Should i replace i with stock and look for a beefier cutter? Any help would be appreciated, This is my first tractor Ive owned and learning a lot, sometimes the hard way.

 

[YanmarFever]

Howse:Rotary Cutter:All Series:Howse Gearbox Parts

 

[Torvy]

Well, since your tractor has more than 40 HP at the PTO, I would not be using something with a 40 HP or less gearbox.

Personally, I'd get a beefier mower. Not sure if the rest of the unit could withstand the beating from a heavier duty gearbox.

 

[Horse Family]

Well, since your tractor has more than 40 HP at the PTO, I would not be using something with a 40 HP or less gearbox.

Personally, I'd get a beefier mower. Not sure if the rest of the unit could withstand the beating from a heavier duty gearbox.

Ok thank you for that advice. Maybe I just put a new gearbox the proper size on this one then sell it to someone with a tractor more suited to it.

 

[oosik]

I think you are looking at future problems. Using a cutter with a 40hp gear box. Fix the unit - sell it. Get a heavier duty cutter.

BTW - welcome to TBN.

 

[ROUSTABOUT]

Input shaft leaking, probably had a bearing problem. I have given gearboxes that size tee total heck. I mean the tractor on a 45 deg angle riding 3" trees over. Bunch of trees at a time. Still have that ole bush hog and it was a free gimme piece of skinned over junk when given to us when i was a kid, single digits. Mid fifties now,. Bush Hog still works, same one. Jimmy Carter was president when we got it, and it was old when we got it.

 

[hosspuller]

Another thought.... You replaced the shear pin... With what ? The shear pin is supposed to shear before anything else is damaged. Doesn't matter if you connect to a 1000 hp PTO when overloaded, the shear pin gives way.

 

[Horse Family]

Another thought.... You replaced the shear pin... With what ? The shear pin is supposed to shear before anything else is damaged. Doesn't matter if you connect to a 1000 hp PTO when overloaded, the shear pin gives way.

So I had never broke a shear pin in about 6 acres of mowing, but hit a small stump. Like a 3 inch stump that was sticking up where I couldn't see it, I was mowing in tal grass and weeds. It broke the shear pin. I couldn't find any the previous owner gave me so I ran to atwoods and bought 1/2" x3 1/2" bolts silver so I'm assuming grade 2. I snapped 4 of them literally just driving through the grass, not hitting anything really, so I googled and people said sometimes bolts are just junk, go to a grade 5. So that's what I switched to today when the gearbox had this issue. I don't know if that's related, but in hindsight maybe all those shear pins snapping were and indication of damage and not just junk bolts.

 

[LD1]

What bolts were loose on the gearbox?

If they were the bolts that hold the input shaft in.....that could explain it. As the input bolts get loose, it would allow too much backlash (clearance) between the gears and they could wipe out as pictured.

You mentioned leaks. Did it ever run low?

While I agree that a 40hp gearbox on a higher HP tractor shouldnt be an issue....as a shearbolt or clutch should protect it regardless. But this dont look like impact damage. Just looks like wear either from backlash adjustment or lack of lube.

But who you bought the cutter off of....was using it correctly. 40hp light duty cutter for pastures that look like lawn. They arent built to smack stumps and hog brush. So if that is your future intended use, you need to look for a heavier cutter. Most all cutters are rated at a certain "capacity". That meaning the diameter of tree saplings/brush they can handle. And most light duty ones are only rated for 1" or less saplings. Which is quite small....like only a little more than half a golfballs diameter.

Medium duty cutters are usually 2", heavy duty 3" and very heavy/extreme 4".

And with each increase in capacity, the gearboxes get much higher ratings. 3" capacity cutters usually have well over 100hp rated gearboxes.

 

[Tinhack]

I see three broken teeth on the input gear. And the breaks look old. That's how it starts. A piece of hardened tooth will wipe out other teeth and bearings in short order. (You can see pieces in the bottom.) That's most likely what caused the seal to start leaking too when the bearing let the shaft move around. Just buy another gear box. The parts to fix that one will cost more than a new one.

I'm guessing that box was making noise, and the input shaft was loose. Most likely why it was sold. Just saying...