755 4WD Front Axle Problem

[kebo]

Best just to load it up and take the whole tractor to the shop, if you don't want to tackle it yourself. That way, the dealer can test it out after the repair is made to make sure all is ok.

After reading your other posts above, it sure seems like something inside the axle has sheared off. When you have it jacked up, with 4x4 engaged and you can see the wheels turning, and you grab the wheel (by hand) and it stops, that tells me that there is just enough friction in the driveline to make the front wheels turn. Grabbing the wheels overcomes the friction in whatever is sheared/busted and causes them to stop, that's obviously why you "have no power in the front wheels".

Good luck with the repair.

 

[carl755]

kebo
I wouldn't mind getting into one of the finals, or even a axle drive shaft replacement, but I don't want to get into the differential, and would rather leave that to the professionals.
I keep hearing from other owners, that most of the problems are usually in the finals. If an axle shaft on one side sheared, or a final failed near the hub, wouldn't the other wheel still pull until it hit something slick? I guess both finals could fail at the same time, or it is something that would affect both sides, like the Ring Gear, or Input Shaft.
Thanks,
Carl

 

[Mechanos]

kebo
I wouldn't mind getting into one of the finals, or even a axle drive shaft replacement, but I don't want to get into the differential, and would rather leave that to the professionals.
I keep hearing from other owners, that most of the problems are usually in the finals. If an axle shaft on one side sheared, or a final failed near the hub, wouldn't the other wheel still pull until it hit something slick? I guess both finals could fail at the same time, or it is something that would affect both sides, like the Ring Gear, or Input Shaft.
Thanks,
Carl

No. The front differential is an "open" differential. The way it is designed, it will direct power to the wheel with the least resistance.

 

[carl755]

mechanos
Guess I am getting too close to this issue..... Glad I have guys like you to keep me on track.

Guess I could still be facing a failure in one of the finals, or a broken axle shaft, but more likely a final. If that is the case, I need to figure out which side.
I can put my finger in the lube hole (left side) and feel the response on the axle shaft, and it is smooth, and positive as I rotate the left wheel back and forth, no hesitation or feeling of slippage whatsoever. Wish I had a lube hole on the right hand side to check that axle.
To me the finals feel good and solid when rocking the wheels back and forth, no loose feeling.
I keep going back to the 'ring gear' thought, but that is not a good one !
Thanks
Carl

 

[Mechanos]

I think it's time to get out the wrenches, put on some rubber gloves (if you so desire) and and start opening things up. At this point.... I just don't see any other way to definitively find the root of your issue. Where are you at in Missouri. If you're not too far from where I'm at, my spare axle might save you a bunch of time and cash over buying all the new seals, parts, etc. depending on what you find out after exploritory surgurey.

 

[carl755]

I think you are right about starting to get into the axle. I am waiting for a friend to assist, who is really busy right now.
I am at the Lake of the Ozarks, snowing here.

I will let you know what I find out when I get into the axle, or give up and take it to the shop, or maybe see if you still have an axle to sell.
The good thing is that the tractor is stored inside, and I really don't need to use it until early in the Spring.

Thanks again to all of you for your suggestions and support
Carl

 

[Mechanos]

You're not too far from me... I'm on the north side of KC. Chances are I'll still have the axle. It's on a parts 855 (same axle as the 755) but it is a different axle than the bigger one in my 955, so I'll never have a use for it.

 

[carl755]

jd110

Removed the left part of the axle at the differential box, and you were right, all six of the bolts holding the Ring Gear were at the bottom of the case. Three had backed out, and the other three were sheared. In a way, it is fortunate that the bottom of the housing is rounded, a perfect place to hold the junk bolts.
There is no damage whatsoever, just need to replace the bolts and the case O-Ring seal.
My thanks to everyone that responded........
Carl

 

[carl755]

I just ordered them, and they are $.70 per bolt. I will use sealant on the new ones, that is for sure.

 

[Mechanos]

That's good news! I would replace them with the exact same bolt and not try to "improve" it with a higher grade bolt. As you can see, they acted like a fuse and kept something else from breaking causing severe damage. Of course, if 3 of them backed completely out, then the torque applied to 3 remaining bolts was double what it should be. Not surprising that the remaining bolts sheared off.

When you go to replace them. Clean the threads in the bolt holes out with some brake parts cleaner to remove the oil from the threads. Then use some medium strength thread locker on the new bolts when you install them. Tighten to 16 ft-lbs.

 

[carl755]

I have already cleaned up the holes, and have the LOCKTITE 243 Blue-Thread locker. I need to check the markings on the 'junk' bolt heads to see the markings, but already ordered new ones, seal rings etc. The tractor is a 1991, and has 600 hours on it. Good idea to improve on the bolts.
I wondered about the torque on the bolts, 16ft lbs seems light to me, but I double checked the shop manual, and that is what it says....
Carl

 

[Zebrafive]

I just ordered them, and they are $.70 per bolt. I will use sealant on the new ones, that is for sure.

$0.70 from JD? Or did you get somewhere else? I too am interested in what size & grade was used.

 

[carl755]

That is the price a dealer gave me. I will post the info. about the bolt once I know know what it is.
Carl

 

[Mechanos]

They are metric bolts: 8mm, Class 8.8

 

[kjung17]

Hey Carl,
Glad you found your problem. Sorry it's so deep. Is there any damage to the gears or case? If there is no other damage, you might get by with new bolts only. This would eliminate the need to "set up" the diff with new ring and pinion. I looked through the technical bulletins on this machine. Most MFWD issues are apparently caused by incorrect front tire overrun. If you would send me the static rolling radius of both axles, I will calculate your ratio. To determine static rolling radius: 1)Park on a flat, level surface. 2)correct all tire pressures. 3)measure the distance from the floor to the center of each hub.:thumbsup:

 

[carl755]

Looks like I am lucky, no damage except for some scrambled bolts at the bottom of the case. I am lucky there was space at the bottom of the case for them to reside, or it could have been much worse. There is some scratching on the back of the case #14, but that is all, the ring gear and pinion look to be perfect.

I do not plan to pick up the bolts, ring seal etc. until next week, so the tractor will be down for awhile longer.
My rear turf tires are 'slicks', and they need to be replaced, so there is a 'slip' factor in any calculations. Thanks for the offer, but it would be a waste of time to do any calculation until those rear tires have been replaced, and to make matters worse, there are almost new tires on the front.
Thanks,
Carl

 

[Mechanos]

I'm not so convinced that this problem was the result of incorrect front tire overrun. If I understand Carl's description, some of the bolts backed completely out and fell to the bottom of the case. That left the remaining bolt to carry much more load that normal. That in combination with driving the tractor on pavement with the front axle engage and the remaining bolts just got overloaded and sheared off.

One thing I'd be concern about is galling. If the axle operated for long in that condition, the ring gear or differential case may have galled with the ring gear spinning on the case.

 

[carl755]

I think it probably is the case that some of the bolts came loose, backed out, and that the remaining bolts sheared when they became loose.
The Ring Gear fits and rides very snugly around the differential gear case #14, and of course it was bathed in axle lubricant, so for the short time it had to ride around and around because it was not bolted down, it appears that no damage was done.
My guess is that no thread seal was used on the Ring Gear bolts originally, some came loose, backed out, broke off whatever, and then I drove the tractor a short distance on pavement with the ring gear in a weakened condition, and the remaining bolts sheared.
I'll hopefully get things put back together sometime next week, and I will report back when the job is complete.
Thanks again!
Carl

 

[carl755]

Well, the tractor is back in operating condition, and all seems to be fine.

I need to replace the rear tires, but I will replace them with the original type, being careful not to get into the "Rolling Circumference" issue. My current rear tires are original, and the front ones were replaced by those that match the original diameter, type, size specifications.
Started playing the pricing game, and do not like what I see. The Goodyear / Titan tires 33X12.50-15NHS Softrac carry a list price of $446.90. Ouch!
My best price so far, is $275.
Carl

 

[kjung17]

Thanks for the follow up, Carl.