Diesel Driveshafts

[wh500special]

This probably would apply to the IH built tractors too, but I figured that since almost all the diesels came to be under CCC guise I'd post here.

It has been noted on numerous occasions that the diesel tractors (782D, 882, 1512, 1572) are particularly hard on driveshafts. Indeed, the PO of my 1512 noted that he's replaced the driveshaft several times on my tractor. The latest shaft on the tractor was actually not a CC part, but was one he had made for the task. He says it is a bit longer but I've never seen an OEM shaft to compare to.

What's the story behind the sacrificial diesel driveshafts? Is it an alignment issue perhaps? Too much engine thrust? An undersized shaft?

I'm curious if the cause is known.

Forgive my ignorance on these things, but I am a complete CC novice. I have a bunch of off-brand tractors that I know pretty intimately, but these Cubs are much more complex and advanced machines than I am accustomed to. I picked up this 1512 with plans to get rid of it, but half a year later it is still sitting here smiling at me every day. A friend said he wants it, but to be honest I hope he never follows thru since it has really grown on me.

Thanks,
Steve

PS- T-MO, I still can't find that stuff I owe you!

[Matt G.]

I think it's a number of things. One, the diesel engines are rubber mounted and move a bit under torque, misaligning the shaft. Two, the rag joint design really can't seem to handle all the torque in my opinion. It's not so much the driveshaft itself that is the problem; the 5/8" CRS shaft is good for about 35-40 hp according to faint memories of some calculations I did awhile back. What happens is, the spherical ball bushings in the couplers on both ends wear, causing the ends of the shaft to wobble around. I think there is a certain engine RPM that happens to have a multiple of the natural frequency of the driveshaft assembly, as both my 782D and the 1512 I used to have had a HORRIBLE vibration at about 1/3 throttle before I replaced the driveshafts in both of them. When the engine runs at that speed, the shaft vibrates even more than at other speeds. The Kubota also shakes a bit at idle, which doesn't help, either. If this isn't fixed, the rag joints don't last much longer, and all of the vibration eventually wears out/crack the spirol pins holding stuff to the driveshaft. The wobbling driveshaft also wiggles the coupler on the trans input shaft, destroying the spirol pin, and eventually, the coupler itself and the trans input shaft if left unrepaired. This usually deforms all of the spirol pin holes in the driveshaft and causes weird wear on the ends, requiring it to be replaced, as well. I had to replace everything except the front coupler on both of my diesels, to the tune of more than $200 per tractor. The biggest problem is the rear coupler on the trans input shaft; if it wobbles, it needs immediate replacement. Buy the QL one, it's the same thing as the 82 series one at 1/3 the price. I've been making driveshafts out of 4140 Chromoly steel lately. If there is any vibration at WOT, something needs attention. My 782D is smooth as glass at full throttle...you cannot tell it is running when sitting on it, save for the noise.

I can't say for sure that this is what's happening, but it's my opinion as to what's going on from what I've observed owning and repairing two of these tractors.

This is also the most annoying repair I've ever done to a Cub Cadet in the 7 years I've been into these...there is very little room to work to remove and reinstall the driveshaft.

[wh500special]

Thanks Matt. I figured you'd take my bait...thanks a TON for the info and for the "watch-outs".

I've noticed that harmonic at about 1/3 throttle. Seems to be a pretty common thing on a 3-cylinder Kubota. My Kubota zero turn (28-hp, 3-cyl) and dad's Kubota SCUT (22-hp, 3-cyl) both do the same thing as the Kub-Cadet at about the same empirical throttle position. And they all shake a bit more at low idle than I would expect.

I bought my 1512 mostly on a whim because the price was so good. But it really has won me over as a great tractor. But I was amazed that the driveshaft, something that CC hung their hat so proudly on, could be a source of expense trouble with these things. It just seems counter intuitive.

This 1512 runs amazingly smoothly at all RPM's except idle and at about 1/3 throttle. I have no baseline to compare with, but I think everything is in good condition but I'll have to give a closer look to the rag couplings and the junction at the pump to make sure it isn't getting loose.

Thanks again,
Steve

[Matt G.]

I emptied my inbox so you can send me whatever message you were trying to send and were unable to. I wish it had a bit larger capacity

[ChrisA]

My 882D blew the rear roll pin on the shaft and then the shaft spun inside the coupler. I figured the parts were ruined anyway and I needed the tractor running, so I just replaced the roll pin and hoped that the now sloppy joint would hold out for a week or two. In fact, it has now been several months ( including fall leaf pickup) and the driveshaft seems quite happy.
Some time ago there was a post (possibly on the old site) by someone who had made his own driveshaft and replaced the rag joints with U joints. Does anyone know if this works out or where the original post might be? I would love to do that with the 882D.

[ChrisA]

I finally found the post by Dave Kamp at Cubfaq. com It is FAQ #25 "How to beef up your driveshaft"

http:cubfaq.com/questions.html

Dave gives a big detailed pdf file with pictures of the conversion.
Thanks, Dave

[Matt G.]

That would probably work good for a solid-mounted engine, but I'm not sure if it would or not for these rubber-mounted engines. U-joints do not like misalignment. I know of someone else on another forum that used U-joints on an 882, and it didn't last very long. The CV joint driveshaft from the cyclops tractors is probably the best upgrade.

[ol'George]

I am experimenting with this coupling to eliminate the rear rag joint on my 782. I have used these successfully in industrial applications.
I thought I'd give it a try as I had it on hand and the rag coupling was sloppy both on the hydro and driveshaft.
Also I made a new driveshaft and put in a keyway for the coupling but retained the coiled pin for the hydro.
Time will tell how well it works, and it makes driveshaft removal simple.

[Sam Mac]

I have a 1210 and I got tired of the drive shaft vibrating. I picked up a 1440 that the engine had been removed from and swapped the trans from it to the 1210. It was a bolt in swap except for the drive shaft that had to be shortened. I cut it then welded it together and put a sleeve over it then welded the sleeve to the shaft just to make sure it wouldn’t come apart. Had to put a disk between the engine adapter and the CV joint to keep the grease in. So far no problems. Also used the rear tow plate with the spring lift assist from the 1440 and the steering box after I modified it. I guess the 1210 is now a 1240?

[aagitch]

WH500, I agree with Matt that I don't know if that's a good application to use ujoints. There's a member from another forum that's done the cyclops cv shaft upgrade and i believe he's pretty happy with it. Don't let your buddy have that 1512, you'll regret. It took me a few years just to find the right smoker for myself. I told the wife "over my dead rotting corpse" will I get rid of it. She said that could be arranged. Ha Ha

Ol George, does that rear driveshaft upgrade allow for flexing? Looks pretty neat.