PTO Shaft to Gearbox Bolts Keep Breaking!

[wirlybird]

Sorry for no updates but been out brush hogging and mowing every day.

The cutter is still breaking bolts. Not frequently but is breaking them.
I think the grade 2 bolt I put in lasted longer!

I am going to try a different PTO shaft and see if it helps.
May just be the way it is.
I carry bolts, nuts and wrenches with me so quick change when it breaks. I actually did shear one bolt the other day.

For other questions - the clutch is in good condition and functions fine.
Gearbox is fine and input shaft is tight, no bearing play.

Thank you to all for the input.

 

[hayden]

Would it be possible to get a picture of the bolt and surrounding mechanism so we are all sure to be talking about the same thing? I have seen bolts holding flange faces together, flange faces with only one bolt holding them together, sleeve couplers with shear bolts through the shaft and sleeve, etc. I don't know exactly what the arrangement is that's causing the problem.

 

[SPYDERLK]

Would it be possible to get a picture of the bolt and surrounding mechanism so we are all sure to be talking about the same thing? I have seen bolts holding flange faces together, flange faces with only one bolt holding them together, sleeve couplers with shear bolts through the shaft and sleeve, etc. I don't know exactly what the arrangement is that's causing the problem.

post #56

 

[ning]

Honestly the only thing I can think of is that your "slip clutch is adjusted correctly" isn't.
When's the last time you checked it?

 

[wirlybird]

Honestly the only thing I can think of is that your "slip clutch is adjusted correctly" isn't.
When's the last time you checked it?

It is fine. I completely disassemble and clean every spring, and it is checked every month. I do this with all of my slip clutches.
It is not "shearing" bolts they only break on the threaded side where the nut is.

 

[RayIN]

Here are the last three that broke. 2 grade 8 and 1 grade 5.
This is a lighter duty cutter and I don't push it hard. I engage and disengage the cutter with engine RPM at about 1500.
I use it mainly for doing fields that are in good shape and just cutting the field grasses.
Most of the time it is areas that I do about once a month to maintain. Next step would be a finish mower or mid mount and mow a little more frequently, but the customers don't need it cut that often.


View attachment 3546902

It's obvious to me the threaded portion is breaking. FWIW I use 3½" bolts, it is a bit too long so I use a heavy flat on each side of the PTO yoke and torque the nut to maximum recommended.
Every gearbox shaft I've touched is hardened steel, good luck doing any machining to the shaft.
IMO you should lighten up your slip clutch a bit, breaking bolts is telling you something.

 

[wirlybird]

It's obvious to me the threaded portion is breaking. FWIW I use 3½" bolts, it is a bit too long so I use a heavy flat on each side of the PTO yoke and torque the nut to maximum recommended.
Every gearbox shaft I've touched is hardened steel, good luck doing any machining to the shaft.
IMO you should lighten up your slip clutch a bit, breaking bolts is telling you something.

it is only breaking one side so it is not actually shearing them. I did use a 3 1/2 and it lasted longer but did eventually break. I think the grade 2 bolts are lasting longer than the 5 or 8's.
Also, they are breaking while mowing nothing more than regular field grass. Cutter is not taking any hits. Not that it is breaking them every day but enough to be a trend and not random chance!
When I am mowing this stuff it barely even affects the RPM it is so easy to cut.
I'm going to change to another PTO shaft and see what happens. Might just be the combo isn't aggregable.

 

[airbiscuit]