Kubota B5100 front differential problem

[mcrossfield]

I recently borrowed a 80's era, badly neglected Kubota B5100 4WD. When you drive the front end will suddenly lock up. Back up a bit and keep going and you're good for a few more feet. It will do this both forwards and backwards. On closer inspection it is missing several bolts that hold the front frame to the engine. I'm wondering if the flexing of the front end is the cause of the front diff locking up, or if it's a separate repair issue. The bolts are broken off in the engine, so they will have to be drilled out and re-tapped. Since it's not mine I'm hesitant to put a lot of work into it only to find more trouble.

 

[davesl708]

Hi. Welcome.

Check the tire size. If the wrong tires are matched up the front axle will turn at a different speed than the rear causing the drive train to bind up.
Sounds like that is what is happening. This may explain the broken bolts as well.

 

[mcrossfield]

Thanks for your quick response. I'll check that out. I'll post what I find.

 

[mcrossfield]

Tire sizes are correct, according to Tractor Data. Additional thought: If the 4WD was disengaged, wouldn't that solve the problem if it was a tire size issue? It does it all the time, regardless of if it's 2WD or 4WD. But with the front wheels off the ground, they turn freely.

I suspect I will have to drill out and retap at least a couple of the broken bolts, to be sure that's not the issue.

 

[davesl708]

You are correct. In 2wd tire size would not create the problem.
The reason the bolts were broken needs to be determined. Otherwise the problem will shear the bolt again.

 

[bigdeano]

My guess would be broken teeth on ring gear and/or pinion, or possibly a bearing completely shot letting the gears jam.

 

[mcrossfield]

Anybody know where I could find a parts diagram of the front differential, so I can visualize what the inside looks like?

 

[davesl708]

You should be able to find a parts list at Kubota's website.

 

[mcrossfield]

Thanks for your ideas and advice. Right bow there are only two bolts left holding the front frame. I am going to drill out a couple of the broken bolts so I can align and tighten it up, then see if the problem still exists. There was a blade on the front, and I suspect the tractor was used roughly. The blade subframe was bolted to the front frame, and those bolts are snapped. That got everything up front moving, which snapped off more bolts. Now the frame moves like it's on a hinge. That movement may have in turn damaged something in the differential.

Amazing what a few decades of neglect can do...

 

[brain55]

These are more than likely separate issues. The frame bolts breaking are because nobody ever checked them. They will loosen up on their own and if left that way will break. The locking up is a gear and/or bearing issue. I would drain the gear oil out of each section to try and determine where to start.

Brian

 

[mcrossfield]

Thanks Brian. That makes good sense. Appreciate the help.

 

[mcrossfield]

Update: This weekend I bolted up the front end and drained the oil from the front diff. There was almost no oil inside, and a few shards of metal came out. I refilled it and tried it, just to be sure, and the problem is still very much there. Probably a ring gear. So much for borrowing the neighbour's tractor to save myself some work. I'll see what he has to say. Thanks again everyone for your help on this.

 

[mcrossfield]

Hey again, it turns out the ring gear stripped. There was hardly any oil in the front differential, and when I split it open the problem was obvious. The pinion is scarred but usable, but the ring gear is shot. Kubota up here in Canada doesn't list parts for that era of tractor. Thoughts on where to look?