MX4700DT nasty, expensive noises

sunandsand · Apr 26, 2022

Next door neighbor has an MX4700DT which he uses hard.

(He also hasn't read the sig line here about taking time to maintain your equipment or your equipment will make time for you to maintain it.)

Anyway, I stopped in today and he has the front of the tractor off the ground (using the front loader bucket) and a bunch of parts scattered around. Did I mention he's wearing a LONG face? Well he is . . .

Tractor runs fine in 2wd, runs ok in 4wd as long as it is going straight, but when you turn in 4wd, it makes nasty, expensive crunching and grinding noises from deep down inside the back end of the tractor.

Dealer cheerfully advises "Bring it down and we'll do diagnostics for you!" I'm sure they will, I'll tow it right down behind Dear Bride's Subie.

He's thinking he broke something at the rear end of the drive shaft to the front diff. I'm not so sure, because I'd think it would make noises in 4wd going straight as well, but I really don't know what's inside there although I'm guessing it is a) hard to get to (he's going to split the tractor in the next couple of days) and b) its going to be expensive (assuming he can even get the parts in some reasonable time frame).

I asked if he had found any metal in the gallons and gallons of hydraulic fluid he's drained out, and he said "No, not yet."

Open to suggestions . . . he's a good neighbor and I do want to help him if I can. I even told him I was willing to come get dirty this weekend if he wanted. He doesn't even need to supply beer, my beverage of choice is Diet Coke.

Best Regards,

Mike/Florida

JWR · Apr 27, 2022

Well,... the only way something changes when it is being turned compared to straight line is that the differential in the rear end is involved. So that says that inside the rear end there is broken hardware between the normal rear end function and the drive headed to the front end via the drive shaft. Not pretty to picture. That's why the thing is being split. Most Harry Homeowners with a tractor for fun are not ready to do that kind of repairs -- one wonders if he has the experience/ability figure out what parts are broken much less how to remove replace -- even of the logistics of getting the parts is solved. Good luck to your neighbor...

sunandsand · Apr 27, 2022

JWR, thank you, and that's pretty much what I expected to hear - major surgery, bring big bucks and have the manual at hand at all times.

I think he can do this (he's split the tractor previously to change the clutch), but I agree that it isn't going to be easy, cheap or fast. He's well equipped with tools and fairly competent in using them, so I think ultimately he will be successful. I'll make sure he has the torque settings and end play measurements available and help if I can.

Best Regards,

Mike/Florida

big bubba · Apr 27, 2022

diet coke? you deserve something with more substance for helping. cheers

BeezFun · Apr 27, 2022

I bought this inspection scope, helps a lot with diagnostics without always taking everything apart. It's waterproof and pretty thin so it fits in any filler or drain hole. It's nice because it's wireless so you can have one person poking it around inside while a helper looks at the phone or tablet screen to figure out what you're looking at.

rScotty · Apr 27, 2022

It sounds like he isjust getting started. If he did a successful clutch job then he is a decent mechanic.

Since the best way to start a repair is to do some simple tests to determine what is broken, so that's probably the stage he was at when you stopped by. It's probably what he was doing. I'd watch for awhile. Maybe you could get him to post here.

Most any mechanic can do basic diagnosis without any tools at all, though some are better at doing that than others.

Basic maintenance doesn't automatically mean failure. Over stressing, overloading, and yanking the controls around are what breaks things.

Basic maintenance can be as simple as checking the lubricating and cooling fluids and still be pretty successful. If the fluids are up to level and not contaminated....just unchanged, then my experience is that mechanical parts may wear faster, but not necessarily break.

rScotty

5030 · Apr 27, 2022

Sounds to me like indiscriminate use of the locking rear differential to me. I bet the locking pins are sheared off and are doing damage in the rear case.

sunandsand · Apr 27, 2022

Noon Wednesday

Inspection scope is a REAL good idea - keeps from taking stuff apart needlessly.

Stopped by, he wasn't there, but he has the front axles out and the wheels are turned 90 degrees. I suppose that makes for a great turning radius. I'll report back on what he's found.

Best Regards,

Mike/Florida

5030 · Apr 27, 2022

Why would you remove the front axles when the noise is in the back end?

This is gonna get interesting I suspect.

sunandsand · Apr 27, 2022

I have no idea why he pulled the front axles, but I will ask him later today. He wasn't there when I stopped by so it is possible he found something and has taken a ride to the Kubota dealer for parts.

Stay tuned . . . you're right, this may get interesting indeed ;-)

Best Regards,

Mike/Florida

rScotty · Apr 27, 2022

5030 said:
Sounds to me like indiscriminate use of the locking rear differential to me. I bet the locking pins are sheared off and are doing damage in the rear case.

I hope it's not another diff locking pin shearing. We just covered that subject pretty well in another thread that was named:

"I'm missing something: Front-end 4-wd"

In that thread, people were real opinionated about whether or not to stop the wheels from turning before engaging the locking rear differential. Some do and some don't and both are sure they are right.

Switching subjects now to the idea of a borescope - I hope he does try it. We haven't gotten one yet but that's mostly just because of the fun to be had solving mechanical things from other clues. I can see where a borescope would be handy.

But for me mechanics is more a hobby than a necessity. There's a large but limited number of possible mechanical breakdowns, and some things are just more fun to solve from more subtle clues.
rScotty

sunandsand · Apr 27, 2022

Update - he had the front axles out because he suspected the front diff. It was fine, so he put it back together.

What he did find was the drive shaft which goes from the front axle to the rear case had a problem. Seems it is somewhat open to the elements and in the 1970 hours he's put on it, enough sand and other crud (tm) got into the internally splined sleeve at the front end of the shaft and wore out the sleeve and the drive shaft. They were worn to the point that you could actually get them to skip teeth by hand.

I didn't see any bright metal, just rust and crud, so I think while those parts were bad (marginal in the tractor where they were kept in alignment, bad when removed and wiggled by hand), that may not be his real problem, though for his sake, I hope it is. A $200 fix on a busted tractor is a gift . . .

He's ordered the internally splined coupling/sleeve ($58) and the short drive shaft ($140+/-) and they should be here at the beginning of next week. The back end of the splined shaft where it goes into the rear case is fine, just the front end where it goes into the splined coupling is shot.

I asked if he had found any metal when he drained the rear case, and he said no, it came out clean, no metal, no sparkly bits. He thinks the noise in the rear end was the front coupling slipping (cogging) and the noise was telegraphing to the rear case. This may be wishful thinking on his part - we will see.

I'll report back after he's installed the new parts.

Best Regards,

Mike/Florida

5030 · Apr 28, 2022

I guess I need to post up the page in the WSM that covers the pins.

loggin · Apr 28, 2022

sunandsand said:
Update - he had the front axles out because he suspected the front diff. It was fine, so he put it back together.

What he did find was the drive shaft which goes from the front axle to the rear case had a problem. Seems it is somewhat open to the elements and in the 1970 hours he's put on it, enough sand and other crud (tm) got into the internally splined sleeve at the front end of the shaft and wore out the sleeve and the drive shaft. They were worn to the point that you could actually get them to skip teeth by hand.

I didn't see any bright metal, just rust and crud, so I think while those parts were bad (marginal in the tractor where they were kept in alignment, bad when removed and wiggled by hand), that may not be his real problem, though for his sake, I hope it is. A $200 fix on a busted tractor is a gift . . .

He's ordered the internally splined coupling/sleeve ($58) and the short drive shaft ($140+/-) and they should be here at the beginning of next week. The back end of the splined shaft where it goes into the rear case is fine, just the front end where it goes into the splined coupling is shot.

I asked if he had found any metal when he drained the rear case, and he said no, it came out clean, no metal, no sparkly bits. He thinks the noise in the rear end was the front coupling slipping (cogging) and the noise was telegraphing to the rear case. This may be wishful thinking on his part - we will see.

I'll report back after he's installed the new parts.

Best Regards,

Mike/Florida

Thank you for the update!! Please keep us posted.

sunandsand · Apr 28, 2022

Went past today at noon, took three pix. The internally splined collar goes on the front of the front to rear drive shaft and connects to the input shaft of the front differential. As you see, that collar is shot. The front of the drive shaft is also gone.

I asked if there was any damage to the splined input shaft of the front differential, his reply was it seems OK and that he thinks the collar wasn't hardened properly. Whether he's right or not, I'd certainly prefer to replace the collar than rebuild the front differential. Aft end of the drive shaft is grubby but the splines are undamaged.

He's going to split the tractor anyway because last time he did it, he did not replace one seal, and it drips (hopefully not on the clutch plate, or he'll be replacing that, too).

I was concerned that the front of the tractor would tip backward as he rolled the back end away, but he says he will have jacks in place. Last time he did it was on a concrete floor (in my hangar) and the FEL and bucket acted as a counterweight and kept the engine level. This time the FEL is off and he's working on a dirt floor.

What bothers me is that the collar and drive shaft show no signs of fresh damage, they are just worn out. When you hear snapping and crackling noises, that tells you something is getting crunched right now, and when you look at that something, it is going to have fresh, bright dings, dents and other damage on it. These parts don't have anything that is obviously freshly busted. I hope I'm wrong here, but I've been fixing busted stuff for almost 60 years and if a broken part is covered in rust, dirt and grime and shows no bright edges or marks, that part has been busted for a while. These noises are new, and come from a different area on the tractor entirely.

(He's in denial. De Nial is a river in Africa, I have seen it . . . it isn't a broken tractor part, I've seen some of those, too. I sure hope he doesn't wind up splitting this a third time to go into the rear diff and replace the diff lock pins and whatever else got busted in there.)

Best Regards,

Mike/Florida

5030 · Apr 28, 2022

The collar is a replacement wear item, I've replaced a few. Never had an intermediate shaft look like that one before. On fact, I keep a collar on the shelf in the spares bin.

sunandsand · Apr 28, 2022

Since the collar is a wear item and the noises seem to be coming from the back of the tractor, I am beginning to suspect that he may indeed have broken off the diff lock pins.

Is there any way to inspect that while the tractor is split, or is there access from the back of the assembled tractor? What I'm trying to do is nudge him to "hey, while you have this thing apart, take a look at . . . " instead of having him put it all back together again, still have the noises, and have to split it a third time.

I'd be happy to look at the thread about that problem, I'm sure it goes into great detail.

Best Regards,

Mike/Florida

5030 · Apr 28, 2022

Depending on the model, on some Kubota's you can remove the back cover that carries the PTO gearing. On both of my M's you can and I have before. Just have to be sure you clean the mating surfaces and apply 3 bond before putting it back on. If you remove the cover, you can see everything inside including the ring, pinion, clutch packs and if there is anything in the lower part of the gearcase. You do have to drain the fluid however and make sure the internal pto drive shaft engages the gearing on the gearset properly. Not a big deal to remove (on mine), at least.

No harder than doing the front propeller shaft actually. Use some caution however, it's heavy. If it has draft control, the upper mount as well as the stopper block for the rockshaft has to come off as well. If it has position control there will be no stopper block to remove.

sunandsand · Apr 30, 2022

Saturday update:

He's getting in deeper and deeper and deeper . . . and I fear he is nowhere near out of the woods yet, or getting there.

Turns out there may be three splined collars.

Power to the front axle starts at the rear differential, goes via a propeller shaft which runs under the clutch housing, connects with another splined collar to the front shaft (the damaged one), then finally into the front axle via the collar in the photo which was worn out.

He split the tractor about a foot to change the leaky oil seal in the bell housing and discovered the propeller shaft is two parts, the front half, which was damaged (photo) and a rear half which runs underneath the clutch and connects the rear differential to the front shaft.

The collar between the front and rear shafts is OK, he removed the telecoping dust collar to change the O rings on the ends (and clean it out, it isn't very dust proof).

Then he pulled on the rear shaft and was rewarded by a "clunk" from deep, deep inside . . . putting the shaft back in didn't re-connect it to the rear diff, it now turns freely and isn't connected to anything.

He is going to have to pull the halves of the tractor much further apart to remove the rear half of the propeller shaft - wires, cables, hoses, linkages, ugh.

Then he has to fish around through that deep dark tunnel to see if he can find the (presumed third) collar and wiggle it back into position to re-install and re-engage the rear half of the propeller shaft. Sounds like he is going to do a colonoscopy on his tractor . . . double ugh.

Hopefully, there isn't a third collar and the clunk was just the loose shaft hitting the housing and it can be wiggled around and pushed back into the rear diff to reconnect it, but at this point I am not taking any bets. His luck hasn't been very good lately. If he IS lucky, he won't have to pull the halves further apart. I have urged him to get the manual, but he prefers to work with pictures from Messicks, on his cell phone (little, itty bitty pictures that you can hardly see).

He still hasn't addressed the original grinding noises in the rear diff which sound suspiciously like they might be broken diff lock pins. I looked at a video on a BX model which has the same symptoms, it shows the broken parts of the pins still in the differential, and not down in the bottom of the casing. This may be why he didn't find any loose parts when he drained the oil.

I've offered him help if he needs or even wants it, so far he hasn't taken me up on it.

More to follow.

Best Regards,

Mike/Florida