Shear Bolt Broke On New Deck. PTO Shaft & Gear Box Holes Don't Align.

FunkeeMunkee · Jul 28, 2021

The tractor is a John Deere 990 and the Rotary Cutter is a Frontier RC2072. I bought the Cutter brand new in November of 2020. I used the cutter only about 6 times to mow a 2 acre pasture. I live in SW FL so the ground is relatively flat, soft and the pasture is just now starting to develop having previously been part of a nursery that we cleared and fenced for horses.

I was mowing last week and had 3 passes to do when I noticed the sound of cutting grass stopped. I looked back to see that about 60 feet of my current row had not been cut. Investigating I found the shear bolt in two pieces right under the gear box. I was a little perplexed by this because the mow deck this one replaced (another Frontier) came with the tractor and I had used it for over 10 years and in some pretty high, thick brush on other properties, numerous times and never once did the shear bolt break. I wasn't the only one driving and you know how other people are less careful with equipment that isn't theirs. And here I am with a brand new deck and a broken shear pin after only 6-7 uses on new pasture.

The original shear bolt is a 1/2"X3.5" grade 8 bolt. I looked without success to purchase one from various local Lowes Depot type stores. TSC had a pack of five, same dimension grade 2 bolts. I bought them because I was going to use them to keep me going until I could locate a grade 8 bolt. I called our local John Deere. They ordered me the recommended bolt for the cutter (which I bought from them). The guy first tried to tell me that the grade 8 bolt was wrong and that I should have a softer bolt. I asked him if this was the case then why did the cutter come new with a grade 8 bolt.

I have turned the PTO shaft to align the holes up to the shaft on the cutter gear box. They align perfectly from top of holes to bottom of holes but not from front to back. Neither the old bolt or the new bolt will move beyond the edge of the hole. It's not even a matter of a tight fit or getting half way and getting stuck. There should be a round hole to slide the bolt through but it looks like one of the two components is jacked at an angle. One one side it looks like the gear shaft hole is too far back at the front of the PTO hole and on the other side the Gear Shaft hole is too far forward in the back of the PTO hole. Is this a manufacture defect?

The original bolt has wear and damage at both spots where the holes would touch the bolt Is this normal wear? Notice how the PTO shaft has wearing on the front of the hole on one side, but on the other side it is at the back of the hole. Is this normal?

I would like to remedy this problem myself if I can. I would like to avoid taking it to the dealer because they will keep it for weeks before they actually look at it and another few weeks before they fix it. But if it looks like it's a defect issue then I'll deal with it appropriately.

I am including photos of the original bolt and images of the PTO shaft and Gear Box shaft holes from both sides. Your advice and wisdom is appreciated.

blee03 · Jul 28, 2021

Sounds like there is either a high spot on the rotary cutter shaft itself, or the pto shaft has a burr or something in it that is preventing it from sliding all the way back to let the hole line up.

I had the same issue when installing a new pto shaft on my old bush hog. I had to get out a file and some sand paper to knock down the high spot on the bush hog shaft before I could properly seat the pto shaft and get my new shear pin in place

the old grind · Jul 28, 2021

When I find a shear bolt unable to go all the way through I rotate the inner OR outer part 180 deg and that's usually all it takes to get the holes to line up. btw, IMO a grade 8 shear bolt is about a useful as a PTO clutch that has frozen up with rust.

bigtiller · Jul 28, 2021

The Frontier RC2072 manual says on page 23 -- 1/2" x 3 & 1/2" grade 8 bolt.

That's what I would use.

Sometimes shear bolts just .... shear off. It's what they do best.

RickB · Jul 28, 2021

bigtiller said:
The Frontier RC2072 manual says on page 23 -- 1/2" x 3 & 1/2" grade 8 bolt.

That's what I would use.

Sometimes shear bolts just .... shear off. It's what they do best.

Every shearbolt application has a specific spec for the correct bolt for that use. Some folks understand that, some don't. This one calls for a grade 8 bolt. That's what should be used.

ruffdog · Jul 28, 2021

Whoa...for the shear bolt joint to work the inner shaft and outer yoke that the shear bolt goes through must not be rusted solid. First, spray penetrating oil in the shear bolt hole and between the shaft and yoke to free up the connection. Lube it good too. Then run the pto on/off so the lube gets in there good. Then you should be able to drop the bolt in. A frozen up joint is just like having a frozen up slip clutch.

workinonit · Jul 28, 2021

I must have missed the part about them being rusted solid. The pics don't depict that.

r porter · Jul 28, 2021

and it was spinning on the shaft for 60 ft without cutting grass.

try rotating the shaft 180 degrees to get the holes to line up.

FunkeeMunkee · Jul 28, 2021

This is an issue misalignment on both sides of the shaft(s).

Hole #1, lets say the PTO shaft - (Female) is aligned like this ---> |
Hole # 2, gear box shaft - (Male) is aligned like this ---> /

The PTO shaft spins and spins and spins and spins. I have rotated the PTO shaft AD NAUSEM and the holes are still misaligned. I've owned the rotary cutter for a total of 8 months and did not start mowing with it until this spring. It is not rusted. There is only a mild amount of surface rust - Florida is wet.

Talking with local dealer again today and sharing these photos he can confirm that the Grade 8 bolt 1/2" x 3 1/2" is correct. Ayup. He also said, after looking at the photos I sent him, "the machine has a slip clutch built into the drive shaft. Without being there to see why the holes are not lining up I would try to adjust the alignment or use a tapered pry bar".

Do I have a miracle rotary cutter that has both a Slip Clutch and a Shear bolt? Cause the specs on these things say Shear Bolt OR Slip Clutch. This is the repair guy.....

When I asked if I used a pry bar and eff it up more would that void my warranty, he said they can come get it for $100 and haul it to their shop.

Reposting 2 photos, now labled and images of the absolute worst pasture anyone has ever had to mow.... it's a wonder I don't roll my tractor or break a shear bolt every time I've mowed it.

Sportsman762 · Jul 28, 2021

I know many rotary cutters use the same gear box for drivelines with a slip clutch and those with a shear bolt. When a slip clutch is used a Grade 8 bolt is substituted for the normal softer shear bolt. This is what you have going on. I had a friend who had a rusted slip clutch and broke the Gr8 bolt on his rotary cutter. Good thing it was not the gear box. My boss had a rusted slip clutch and took out both blade gearboxes on his 8'.

To me those pastures look like a dream to mow. Nice and smooth and flat and square.