Kubota B5100 front differential problem

   / Kubota B5100 front differential problem #1  

mcrossfield

New member
Joined
Mar 16, 2016
Messages
8
Location
West Brome, Quebec
Tractor
Kubota B5100
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.
 
   / Kubota B5100 front differential problem #2  
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.
 
   / Kubota B5100 front differential problem
  • Thread Starter
#3  
Thanks for your quick response. I'll check that out. I'll post what I find.
 
   / Kubota B5100 front differential problem
  • Thread Starter
#4  
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.
 
   / Kubota B5100 front differential problem #5  
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.
 
   / Kubota B5100 front differential problem #6  
My guess would be broken teeth on ring gear and/or pinion, or possibly a bearing completely shot letting the gears jam.
 
   / Kubota B5100 front differential problem
  • Thread Starter
#7  
Anybody know where I could find a parts diagram of the front differential, so I can visualize what the inside looks like?
 
   / Kubota B5100 front differential problem #8  
You should be able to find a parts list at Kubota's website.
 
   / Kubota B5100 front differential problem
  • Thread Starter
#9  
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...
 
   / Kubota B5100 front differential problem #10  
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
 

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