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...

 

[LittleBittyBigJohn]

Put me down on the list that says get a gearbox and mow on. Looking at tractor data, your machine should have 45 hp at the PTO when new. I don't see that destroying a 40hp gearbox in the short or long term. I think LD1 has a good theory, pinon shaft backed out and extra backlash wore the gear set out.

 

[John0829]

That gear box failed for some other reason, definitely NOT what you did hitting the stump. I have a 40hp gearbox on mine and my rule is if the tractor can safely ride down the brush it gets cut. As has been said the shear pin is there to protect the gearbox and I have found most of the time they shear way to easy, that is why I finally put a slip clutch on mine.

 

[Horse Family]

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.

The first bolts i noticed that were loose were the bolts holding the gearbox to the top deck of the tractor. I had to remove the stump jumper in order to tighten them down. Two the the four bolts were missing the lock washers. I tightened them all down, and then after using the brush hog more, the same ones came loose again. So I retightened, this time with red locktite.

We did notice that the bolts around the input shaft had also gotten loose.

I think I have learned that in the future, if I buy any used equipment, that I will do a much more thorough look over of the equipment, as well as taking the time to go through it and check all bolts etc.

I do think that after I repair this one, I will sell it, and look for something that is a heavier duty cutter.

 

[2manyrocks]

By the time you make these repairs, you know what you've got vs buying another used cutter unless its new.

Bolts may be coming loose due to vibration or perhaps new bolts, washers, etc., would finally tighten enough to not loosen up? Do bolts actually wear out and loose their ability to stay tight?

 

[Horse Family]

You guys are awesome, I so appreciate the help and feedback. So its clear I need the new gearbox, now just trying to figure out which one to get -

On Surplus center, all the RC51s are ratio 1:1.93

According to the tag on mine my current ratio is 1:1.47

how important is it that the gear ratio remains the same?

I see they have some RC30s that appear to have the same gear ratio as mine - 40 HP Omni Gear RC-30 Rotary Cutter Gearbox 1:1.46 Ratio Model 250001 | Featured Items | www.surpluscenter.com

But I don't know what the difference in the two are.


I also see this one at agri supply - seems to have the same HP rating and ratio - Gearboxes-Rotary Cutter Gearbox

If anyone has any experience and can help me choose id appreciate it!

 

[5030]

I agree, the previous owner started the destruction of the gearbox, all in takes is one chipped tooth to start the destruction and because multiple teeth engage the pinion at one time, you won't feel anything until multiple teeth are destroyed, except maybe a little vibration.

Couple of other items that need to be addressed:

One, lift the cutter up and make sure the blades are FREE swinging, They have to be free and not rust locked to the pivots and if they are badly worn, replace them... I'll give you a web site where they will have EVERYTHING you require and their pricing is excellent and service is as well. I get all my replacement parts for both my shredders from them as well as 3 point parts like bushings and overrunning couplers, something you really need for ANY shredder as a shredder will destroy your PTO brake in pretty short order from freewheeling if the PTO is disengaged while the shredder is turning at operating rpm.

You can get everything you need, including the pivot bolts and lock nuts as well as the blades and gear box and even the correct shear pins (something you need and not Grade 5 box store pins) from Agri Supply. I think their website is www.agrisupply.com, if not, look it up on Goggle or Duck Duck Go, whatever browser you use. I buy a ton of stuff from them, shipping is very reasonable, delivery is always excellent and nice folks to deal with.

 

[5030]

Do bolts actually wear out and loose their ability to stay tight?

Especially if not torqued properly and Locktited. I use thread locker on everything threaded, subject to stress and vibration. Usually Blue Threadlocker but sometimes (depending on application), red high strength and not the knock off Chinese crap either. Always Henkel Loctite. USA made (sometimes Mexico) but never China. It's not cheap but the good stuff never is today. I buy it in 250ml bottles.

 

[ROUSTABOUT]

You guys are awesome, I so appreciate the help and feedback. So its clear I need the new gearbox, now just trying to figure out which one to get -

On Surplus center, all the RC51s are ratio 1:1.93

According to the tag on mine my current ratio is 1:1.47

how important is it that the gear ratio remains the same?

I see they have some RC30s that appear to have the same gear ratio as mine - 40 HP Omni Gear RC-30 Rotary Cutter Gearbox 1:1.46 Ratio Model 250001 | Featured Items | www.surpluscenter.com

But I don't know what the difference in the two are.


I also see this one at agri supply - seems to have the same HP rating and ratio - Gearboxes-Rotary Cutter Gearbox

If anyone has any experience and can help me choose id appreciate it!

2 to 1 cuts better. If I'm looking at a cutter, if it ain't close to 2 to 1, meself will let it pass. That babe will cut grass like a lawn mower.

 

[LD1]

Not sure the difference. They seem to read and spec nearly identical

 

[2manyrocks]

Can't go crazy with it, but if you want a bolt tight, a breaker bar seems to get a bolt tighter than a short handle ratchet wrench. Given the labor involved to fool around re-tightening bolts, I'd think about installing new bolts, nuts, washers, and lockwashers along with locktight as 5030 recommended. I'd also clean the mounting deck surface in case rust is keeping the bolts from firmly locking in place.