755 4WD Front Axle Problem

carl755 · Jan 13, 2011

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 · Jan 13, 2011

carl755 said:
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 · Jan 13, 2011

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 · Jan 13, 2011

They are metric bolts: 8mm, Class 8.8

kjung17 · Jan 13, 2011

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 · Jan 13, 2011

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 · Jan 13, 2011

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 · Jan 14, 2011

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 · Jan 19, 2011

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