Rotary Cutter Drive Shaft Sheared!

[Haoleguy]

Well another first happened to me today. I have been cutting fields and forest areas for the past few days and today I stayed more to the woods to stay cooler. Well I was buzzing along at 2mph at 1700rpm with my Deere MX5 and it sounded like I hit something, not unusual occurence, and I kept on going and after 100ft or so I felt like everything was too quiet. I looked back and I saw the PTO shaft turning but then at the path behind and there was no cutting going on. Disengaged PTO lever and raised the MX5 to find I had no turntable and blades. Went back to area where I think it happened and sure enough there was the blades and turntable with the 2-3in drive shaft sheared off! Couldn't believe this could happen as the MX5 had been bullet proof for 5 years. I was overheating at this point so I did not open the gear box. Searched this forum for ideas on how this might have happened and how difficult the fix might be but didn't find any ideas. I'll talk to my dealer tomorrow when he opens and get an idea on the best way to proceed. My guess is to let him repair and check it out before reuse. Any thoughts from this group on the possible cause to fatigue the shaft and whether this is a straightforward fix?....Thanx.

 

[sweettractors]

Look at the shaft at the shear point and check to see if there is any discoloration on the surface that would indicate a previous partial break. I had this to happen to me on a 6 ft pull type AC brush Hog (hit a rock). All you need is a output shaft. Pretty straight forward mechanics. You have got me worried now, my Son is using his MX7 today in some pretty rough work. I thought those would be bullit proof for 20-30 years at $3500 a pop. Ken Sweet

 

[Haoleguy]

Hi Ken - I was pretty much surprised to have the drive shaft shear off. On first view I did not see any discoloration on the top of the break. The break is pretty clean except for a small rough line of metal. I will check closer tomorrow..thanks for the tip. Other than one other case I'm not aware of this to be a problem with the MX series. Mine has been used to reclaim pasture and turning wooded areas into pasture with followup cutting in subsequent years to get good ground cover growth. I have hit my fair share of unseen rocks and logs with no issues. I had been cutting today for 4 hrs straight when the shear happened. As I said it looks like a clean break and no indication it was going to give. Maybe there is more to see in the gearbox.

 

[gauthier]

If its made of metal it can break,metal in those is probably no different[probably from same mill] as my cheapo kingkutter.

 

[Ford tractor]

If its made of metal it can break,metal in those is probably no different[probably from same mill] as my cheapo kingkutter.

I got a box of donuts that says your wrong on that one! (same as KK)

There was probably a casting imperfection or else a faulty heat treat. Get a new shaft and should be good to go.

 

[Dead Horse]

I have seen this several times on JD cutters and in fact replaced both spindles on my MX10 over the last several years. On the heavy duty 6' cutter JD actually warrantied the whole gear box and sent me a complete new one. on my light weight 613, I have beat the heck out of it for 12 years and it is solid. I think JD chinzed on the steel on the larger cutters. I know I will never buy another one.

You can buy the gear sets from JD, and do the r&r yourself. The toughest part is getting the old bearing off the stub of the spindle. Course you can always just purchase a bearing set and be done with that aspect of the job.

I can walk you through the repair job, it is not at all complicated. Only real tools you need are some wrenches and snap ring pliers.

I think the reason this happens is the disc is pretty big and when it makes contact with the ground because of a bump, or small hill or something like this, it causes the spindle to flex, eventually weakening it to the point of failure.

Man, when that disc with blades attached come shooting out from under the mower, you don't want to be standing there, that is for sure!!!!!!!!

 

[rd_macgregor]

Does this unit have shear bolts or a slip clutch? From what I've read, one issue for those with slip clutches is that owners never adjust/reset them, so the clutch plates freeze (rust?) together and don't slip properly. When this happens, something else has to give. I guess a sheared shaft is likely a bit better than stripping all the gears, though!
Did the blades hit/damage the deck at all?
BOB

 

[gauthier]

Not only same mill,same fabrication place too probably[probably both in china:laughing:],and yeah agree there was a defect that contributed to the break. But everything has some defects,so that and hard use probably did it,and like we all know,things break[least we know deere hogs break]

 

[sweettractors]

Not only Deere cutters break, Other do as well. I sell a lot of gearboxes and output shafts for many other brands manufactured. Ken Sweet

 

[sandman2234]

Metal fatiques and breaks, simple as that. I sold my Ford 1100 the first time and the new owner drove it across his yard, nothing on it, and the rear axle broke. Had we not been friends and completely honest with each other, it could easily been assumed that one or the other did "something", but I am convienced that neither did. I was working in a QA lab at the time and took the shaft parts into work and had the Chief Metalurgist look at it. His answer was "torsion fatigue" which was accounted to the right brake not working as well as the left, plus several other factors which cause the left axle to load/unload more than usual. Loading of that bushhog output shaft is done when he hits something, and unloading is done when it is spinning without a load, allowing the weight of the disc to catch up with it.
I don't know much about JD gearboxes, but I do have one on a rusted out frame that might be a candidate for a broken gearbox instead of a deck rebuild, if it matches your gearbox. Assuming that an MX5 is a 60" cut, it is probably too small since it is on a 48" mower.
David from jax