755 4WD Front Axle Problem

[carl755]

New to site.

I have a 755 MFWD (1991) and have lost power in my front axle when in 4WD.
Trying to figure out where the problem is located. I know I have power in the
front drive shaft, no unusual noise, just no power in the front wheels.
I drained the lubricant, and found no metal shavings.

I was moving some dirt, moving forward and backward, then traveled on a blacktop road, forgot to take it out of 4WD. Found the problem a couple of days later.

My key issue is how to trace the failure to left side, right side etc. The front wheels will turn, but have no pulling power.
I have dropped the front drive shaft, and have access to the input gear, so can turn it by hand.

 

[Mechanos]

Hmmm.... as far as I know, ther are no keyways or shear pins in any of the front axle connections. All the gears are splined to their shafts. My first thought is that a gear has decided to spit it's teeth out. You may have to start opening up the front axle to find the culprit.

If it does turn out to be a shelled out axle component, shoot me a private message... I have a spare front axle assembly (minus the right knuckle/hub) that I'm not using.

 

[dsmau]

If you lift the front end off the ground, will one wheel spin in one direction while the other in the opposite when you make one of them turn? How much resistance do you feel?
This should help identify where the problem is.

 

[kebo]

If I understand you correctly, since you have dropped the front driveshaft and can turn it freely by hand, and NEITHER of the front wheels turn along with it, then you have either broken the input shaft that the pinion gear is on, or as others suggested the teeth on the pinion (and/or ring gear) or broken off. If the problem were only on the left side or right side, then when you turn the input shaft the wheel on the opposite (good) side *should* rotate.

 

[kjung17]

You say you can turn the input shaft but the front wheels do not turn? Looks like there is a reduction gear between the input shaft and pinion shaft on that little fella. Here is a parts blow out. Error java.lang.NullPointerException
Let me know if the link doesn't work.

 

[carl755]

mechanos,dsmau,kebo,kjung17

Thanks for your replies. I'll try to answer all of your questions.
First, the wheels will turn most of the time, and they do counter rotate as they should. There is just no pulling power. Something is sheared or broken, but may be touching to the point that the wheels still will turn, most of the time.

Thanks to the lube fill hole, I can tell when the left axle shaft is turning, but I do not have that luxury on the right hand side (no view hole). I have been told that "if the input spins and no wheels move and the shaft on the left spins, the problem is on the left side final. If the input spins and no wheels move and the shaft on the left does not spin the problem is in the right side." in my case that points to the right side.
What throws me is that sometimes both wheels turn, one counter rotating, but you can stop them very easily. It is almost like a shaft is severed, yet touching.
Any ideas what a JD shop would do with something like this, just start a tear down?
It appears to me per my "Shop Manual" one must start at the (hub) final to get into the axle, unless of course you would go in at the differential.
Yesterday, I removed the right hand wheel, and turned the spindle that holds the wheel, and it sounds just fine, no noise, just the normal pressure one would feel when turning gears in a shaft.
I have drained all of the lubricant from the front axle.

Thanks........

 

[jd110]

I had one that sheared all the bolts holding the ring gear on. Sounds like you may have the same thing. #15 in illustration. I would think if you had teeth stripped on a gear, you would hear some noise when turning the axle or driveshaft.

 

[Mechanos]

Well, if you done all the diagnosing that you can do, I don't see any other choice but to start a systematic tear down. Based on what you've described, I'd be looking for either a shaft that twisted in two or a stripped splines between one of the gears and it's shaft.

 

[kjung17]

Here is a better pic of that differential. I would check the input shaft #18. I suspect the spline connection between 18 and 19. This failure would produce very little material and the symptoms you describe. This would also be a relatively cheap fix.

 

[carl755]

mechanos & kjung17 - Thanks to you both

kjung17 I have the 'cover' #59 already off. I have been turning the input gear # 19 for my testing since I removed the cover. Is it your thinking that the splines on #18 are just holding enough that I can turn the wheels by hand using the input gear #19?
If true, it appears that #18 will simply pull out of the differential. That indeed would be a simple fix.
I can't get to it until later next week, but I will let you know what happens.

Looks like we may be in for some snow in MO.

 

[kjung17]

Sorry jd110, didn't mean to step on your pic. You must have posted while I was researching.:laughing:

 

[carl755]

kjung17

I just took a look under the tractor, and I gave you bad information in my last post, sorry about that!
I have been turning the axle by gear # 22, not #19. The parts you describe stay in the cover (# 59 ) when you remove that cover. I may have simply been testing the axle beyond the problem, if you are correct.

 

[kjung17]

let us know what you find. Good luck.

 

[carl755]

kjung17

I just looked at the cover # 59 which holds haft #18, which slides onto the gear # 19. I pulled the two parts from the cover, and found the splines to be like new, so that is not the problem sorry to say, as that would have been an easy fix.
Thanks - Carl

 

[carl755]

jd110
The front end of my tractor is up off the ground, and I can either turn the wheels by hand or by the 'input gear". I seems to me that turning the wheel by hand requires a normal amount of pressure. I recall when I first found the problem I jacked both ends of the tractor off the ground, and had it running while in 4WD. The drive wheels were both turning, and then I grabbed the right hand wheel and it stopped, and the left hand wheel started turning, as it should (counter rotate). I then lowered the front end with the back end still up on the 4-wheel jack, and the front wheels would not drag the tractor, no power.

What happened when you sheared the bolts #15 in the Ring Gear?. Was there room for them to simply drop to the bottom of the case, without any other damage, and make no noise once there ?
Is there enough pressure against the ring gear #12 that it could still turn the wheels, although not pull the weight of the tractor?

Thanks,
Carl

 

[kjung17]

Oh well. We had to try. I guess you'll have to dig into the axle. You are certain that your mfwd selector is working properly?

 

[Mechanos]

Based on your latest info, it is also possible that there is nothing wrong with the front axle at all. There is a chance that the problem lies in the transaxle and the MFWD output shaft. If that turns out to be the case, let me know... I have a spare transaxle as well. :laughing::laughing:

 

[carl755]

Yes, I checked the lever when I first lifted the tractor off the ground. With it running and in 4WD, the front wheels were turning. Later I then slid under the tractor and moved the front drive shaft shield to see what kind of power I had in the front drive shaft, couldn't stop it with my hands, so I was reasonably sure I had sufficient power to the front axle.
Thanks for asking.
Carl

 

[jd110]

Carl, yes there is enough drag to make the wheels turn with no load. I can't remember right now whether the bolt head fell to the bottom or if they stayed in the carrier. There might not have been enough room for them to fall out of position once they sheared off.

 

[carl755]

jd110
That is interesting, and it made no noise?
If I did not want to attempt the repair myself, would I need to drop the entire front axle, or haul the tractor to the shop, looks like a huge task.
Thanks,
Carl