Driveshaft breakage??

Mon Sep 30, 2013 10:16 pm

Since I haven't ran my fcub much before the drive shaft broke. I noticed two circles on the diameter of the split ends. The darker ring was on the outer edge that tells me it's an older fracture. While the inside diameter was lighter in color so it's a fresh break. The drive shaft actually whipped inside the housing. I'm thinking I did the final break by snowplowing using the solid link instead of having a chain in its place. When the blade would bind the shock went to the drive shaft. The shoes on the plow aren't that good too. With the solid link on the plow lift it has down pressure. I'm pretty sure it finished off my already fractured drive shaft. Now Ralph sold me the new looking parts which I will magnaflux to make sure there are no fractures anyway. But by eyeing it I don't see any hair line fractures. Now I feel the need for an inner drive shaft support or a drive shaft girdle/support. So it can't bind or bend again. I have both designs in my mind. One is installing a flanged bearing block. The other is making a thicker drive shaft in the area were it wants to flex. I can't put this back together knowing there is a weak spot there only waiting to fracture again. Any thoughts? Is the fcub drive shaft fracturing a reoccurring problem on the Fcubs?

In the future I do want to get a heavier duty super A, or 140. The fcub isn't a real workhorse. It has its limits. But it will never see hard work again just mowing.

Re: Driveshaft breakage??

Mon Sep 30, 2013 10:29 pm

Before you get too carried away, you should know that a broken drive shaft is very rare. I think yours may be the first, or maybe the second one i have ever heard of, and have been on this forum for over 10 years, and on the ATIS forum for several years before that.

Re: Driveshaft breakage??

Tue Oct 01, 2013 12:23 am

My fcub was used on a local farm here for cultivating the corn fields. They had a big JD for planting and soil prep.

Re: Driveshaft breakage??

Tue Oct 01, 2013 7:11 am

Why not just fix the blade? Next will be the engine mount broke off.

Re: Driveshaft breakage??

Tue Oct 01, 2013 9:09 am

A chain on the blade only helps in the up/down direction.

When you hit something with the blade, the shock is transferred back through the solid arms to the mounting brackets, and then into the tractor. Since you can't push a chain, this is a necessary evil. The only solution is to be more careful. Go slower.

On the driveshaft, it is definitely NOT common to break. First one I've heard of.

Obviously the shaft was first damaged a long time ago. Someone really had to bash that tractor around HARD to do that.

Any sort of intermediate support for a shaft of that diameter given the limited RPMs and horsepower just isn't necessary. Not saying don't do it, but you really don't need to.

Just don't use the tractor for a battering ram and it will outlast you.

Re: Driveshaft breakage??

Tue Oct 01, 2013 11:26 am

My thought is you are way over thinking and worrying about this. You had a predamaged, long before you got it, drive shaft that failed. Snow plowing or anything else won't break a good drive shaft or a whole bunch of us would be replacing them all the time. Somebody damaged it when they were forcing it back together after a split, or maybe just put in a bent one to get good PTO splines, or who knows......Just split it and put the replacement shaft in. In this case with the shaft having whipped around I would do a double split one at the bell housing to check the clutch, TOB, and hangar and set the fingers while I'm in there and also take a look at the pilot bushing. The other split would be at the transmission to actually replace the shaft. I sometimes forget a little smear of grease on both bushings before putting it back together.

If we haven't convinced you the extra bearing is unneeded yet think about this. You have to get the bearing EXACTLY centered around the perfectly straight shaft. If there's a slight bend in your shaft; or your bearing, lets say, raises the middle of the shaft 1/100 of an inch making it an ever so slight "U" shape. When the shaft rotates 180 degrees from it's starting point, it will have to flex in the bearing 2/100" because the ends are fixed where they rotate and now you've fixed the center position as well. I figure you have bent a piece of metal back and forth to break it before? Here were talking up to 1600 or so times a minute for a couple hours. You'll definitely have another broken driveshaft.

Re: Driveshaft breakage??

Wed Oct 02, 2013 7:36 am

I have to agree with others, this is an EXTREMELY rare problem, maybe the only time I've ever heard of it either. Based on the way the cub is built, there's really no way to even put "lateral pressure" on the drive shaft, unless the engine to torque tube bolts are loose, or the torque tube to transmission bolts are loose. There's no way, even slamming into something with the blade, that would cause a lateral force on the drive shaft, causing it to deflect as you have described. It's just not possible. However, if the tires bite in, you could put undue "torque" on the driveshaft. There are several things that would give first before damaging the driveshaft in this occurance, the easiest and most obvious is the clutch.

So, thinking this through, the only way to really put extra load on the driveshaft while working the tractor would be to overload it with wheel weights (so it can push/pull more than it's designed to) and/or installing an aftermarket clutch with more gripping power, or adjusting the clutch so that it's grabbing more than designed to.

I've had dozens of cubs, and plowed way more snow and dirt than a cub was probably designed to. The very first thing that will happen if you hit something with a blade is the back wheels will spin (assuming you've got no more than 2 sets of wheel weel weights on, or loaded tires and one set of weights like I used to run, however both are within the recommended "weighting" of a cub). Yep, hit a root while pushing dirt, or hit a concrete curb while plowing snow, the tractor will stop dead in it's tracks, and one of the rear wheels will start to spin before you can ever think of getting your foot on the clutch. I've done it MANY times! If the tires actually both grip, it will stall the tractor. Done that many times too. Either way, you're still not really putting much stress on the driveshaft because of all the gearing in the final drives and transmission.

Putting a pilot bearing in the driveline is a waste of time. Totally useless, and would probably cause more problems than you've had already. Either something is wrong with the tractor, or the drive shaft was just faulty. My guess is something on the tractor is not put together correctly! It's probably been split for a clutch replacement, and the bolts were never installed correctly, or have worked loose, and the torque tube is flopping around on the engine block, or, it has happened in the past, and all the bolt holes are worn, and it's just not put together correctly. Could be at the transmission too, but my guess is the engine to torque tube.

Re: Driveshaft breakage??

Wed Oct 02, 2013 7:58 pm

I agree with the others! Only ones I have seen that were even bent had a tree to fall on them

Re: Driveshaft breakage??

Wed Oct 02, 2013 9:44 pm

May have been a flaw from manufacturing. I found a rear axle that had what appeared to be a lengthwise crack. After slicing it up with a cut off wheel, It appears it was a casting flaw. Probably would have never caused any problem other than a minor oil leak, which it had, and i was in the process of doing a complete refurbish when I noticed it.

Re: Driveshaft breakage??

Wed Oct 02, 2013 11:01 pm

I have repaced a few broken driveshafts over the years.. I is not a common problem Usually its a defect in the manufacturing. also I have had a cub myself that I bought that the driveshaft was bent. i ran it for years before it broke. I also replaced one that the previous owner got used out of a cub that was in a fire.. It broke right at the transmission.. it does happen but not a common problem.