PTO Shaft to Gearbox Bolts Keep Breaking!

[bigtiller]

Have you made any witness marks on the slip clutch to confirm that it is slipping?

Maybe try loosening each tension bolt on the clutch an eighth of a turn and check it again for slippage and/or excess heat.

 

[Roadking52]

Check to see if your pto drive shaft is bottoming out when you lift the mower. It may need shortening. You should also never run a grade 8 bolt in that application. You want that bolt to be the weak link. It’s a lot cheaper than the other parts you can break.

 

[Zork]

A few things I can think of.
1- Is it a shear bolts? Slip clutches do not require shear bolts in the shaft as the clutch does the protecting of the gearbox.
2- Is the shaft too long and the back-forth movement is shearing bolt?
3- Are you over torquing the bolt when you tighten it?

 

[bill karrer]

You say the slip clutch is adjusted properly, but is it rusted together? Has the clutch ever slipped? Loosen the slip clutch until it does slip and gets a bit warm to the touch. This will assure the discs are free of rust and corrosion. Readjust clutch. Not a bad idea to do this at the beginning of every season. Use only grade 8 or 10.8 metric bolts and let the slip clutch take the pounding.

 

[boatmoter]

I run a 5 foot brush hog on my JD 3032E. I have used this cutter for years for lighter duty work. Mostly just cutting field grasses on nice flat areas.
I do run a slip clutch PTO shaft. Clutch is adjusted correctly and is in good shape.
I usually run grade 5 or grade 8 bolts where the PTO shaft connects to the input shaft on the cutter.
This thing consistently breaks the bolts. I break one every week or two. I am not hitting anything like dirt clumps, sticks stumps etc.
The bolts all break at the same spot, which is about an 1/8 inch from where the threads meet the smooth shank.
The slip clutch fits snuggly on the gearbox input shaft so there is no wobble.
The gearbox is in good shape, spins freely and has no slop. Gearbox mount is solid and the gearbox is aligned straight.

I also run a 5 foot Woods BrushBull on the same tractor and have never broken a grade 5 bolt.

Any thoughts on this one?

we always use a regular soft bolt, the bolts are supposed to shear to protect the shaft and other components. thats the whole reason behind not making it a splined shaft. use regular cheap bolts, we used to use a 3/8 bolt.

 

[Pinecrest]

I run a 5 foot brush hog on my JD 3032E. I have used this cutter for years for lighter duty work. Mostly just cutting field grasses on nice flat areas.
I do run a slip clutch PTO shaft. Clutch is adjusted correctly and is in good shape.
I usually run grade 5 or grade 8 bolts where the PTO shaft connects to the input shaft on the cutter.
This thing consistently breaks the bolts. I break one every week or two. I am not hitting anything like dirt clumps, sticks stumps etc.
The bolts all break at the same spot, which is about an 1/8 inch from where the threads meet the smooth shank.
The slip clutch fits snuggly on the gearbox input shaft so there is no wobble.
The gearbox is in good shape, spins freely and has no slop. Gearbox mount is solid and the gearbox is aligned straight.

I also run a 5 foot Woods BrushBull on the same tractor and have never broken a grade 5 bolt.

Any thoughts on this one?

Are you buying your Bolts from the same place? They may not be Grade 5 even though clearly marked on the head. There are a lot of counterfeit grade 5 bolts made in China on the market
and other than buying from a reliable vendor I don't know how to tell.

 

[henerythe8th]

The bolt is not being sheared. It is being killed by countless rapid lateral shock loads that fatigue the metal at the weakest point...the bottom thread. I wonder how close a fit the hub and shaft are? There should be no slop there. What actual diameter are the holes in the hub and shaft?

After reading several pages of issues THIS needs further investigation!
The fit of the flange to the shaft should be "near perfect".
In other words, no slop between the OD of the shaft and the ID of the flanged piece.
If there's "wiggle" then that's likely the issue!

 

[Gord Baker]

I run a 5 foot brush hog on my JD 3032E. I have used this cutter for years for lighter duty work. Mostly just cutting field grasses on nice flat areas.
I do run a slip clutch PTO shaft. Clutch is adjusted correctly and is in good shape.
I usually run grade 5 or grade 8 bolts where the PTO shaft connects to the input shaft on the cutter.
This thing consistently breaks the bolts. I break one every week or two. I am not hitting anything like dirt clumps, sticks stumps etc.
The bolts all break at the same spot, which is about an 1/8 inch from where the threads meet the smooth shank.
The slip clutch fits snuggly on the gearbox input shaft so there is no wobble.
The gearbox is in good shape, spins freely and has no slop. Gearbox mount is solid and the gearbox is aligned straight.

I also run a 5 foot Woods BrushBull on the same tractor and have never broken a grade 5 bolt.

Any thoughts on this one?

Take note of clutch plate spacing and loosen off bolts. Be sure the clutch is not Stuck. Run the machine level, Front to rear and side to side. Keep sides 4" or more OFF THE GROUND.

 

[RESINC]

1
Find the hardest grade and largest diameter bolt you can buy that you fan fit in. You may need to go to a bolt specialty shop.
2. When you engage the Bush cuter, engage at lowest rpm possible. 1500 IS TOO HIGH.
I have an 8ft JDeere. I had the same problem. I took it to dealer. They said nothing was wrong with the cuter. They said do 2.
I Took the initiative to do 1. Problem solved. Good luck.

 

[RESINC]

I run a 5 foot brush hog on my JD 3032E. I have used this cutter for years for lighter duty work. Mostly just cutting field grasses on nice flat areas.
I do run a slip clutch PTO shaft. Clutch is adjusted correctly and is in good shape.
I usually run grade 5 or grade 8 bolts where the PTO shaft connects to the input shaft on the cutter.
This thing consistently breaks the bolts. I break one every week or two. I am not hitting anything like dirt clumps, sticks stumps etc.
The bolts all break at the same spot, which is about an 1/8 inch from where the threads meet the smooth shank.
The slip clutch fits snuggly on the gearbox input shaft so there is no wobble.
The gearbox is in good shape, spins freely and has no slop. Gearbox mount is solid and the gearbox is aligned straight.

I also run a 5 foot Woods BrushBull on the same tractor and have never broken a grade 5 bolt.

Any thoughts on this one?

In addition, good clutches and clutching very important. Also lower RPM when engaging