'L' Series Correct Frt Gearcase Shimming - Bevel Gear

[VT_Kubota]

What I need is someone here to help me with the correct way to set gear backlash in the front axel case. I found a very worn lower bevel gear in the bottom of the gearcase on the rt. side while I was replacing the seal. I ended up taking the whole case completely apart for cleaning and to check all of the bearings after seeing all the metal missing from that gear. The bearing on that gear was bad also but all the others were OK. The pics of the gear look to me like either a bad heat treatment of that gear or an incorrect setup of the lash originally. Notice that there is almost equal damage to each tooth and it is also in the same area of each tooth. I would not expect that kind of damage if a piece of something was rattling around in there (?).

When I reassembled things, the gearcase was WAAAY too tight when I tried to turn the hub. Since I reused the original shim, I am guessing that either the gearcase was improperly shimmed originally or ?? If I remove the shim (it is a 2.0mm;the parts book shows 7 thicknesses from 0.8mm - 2.6mm) there is a bit more lash than I would consider ideal.

The odd thing to me is that the gear can be driven upward until it hits the casting but this places it more deeply into the ring gear for the hub further decreasing lash + increasing binding. Does this gear and bearing assy just "sit" (via gravity) down against the shim(s) and snap ring in the bottom of the gearcase since there is nothing that shows any shims between the gear and the bearing?? I guess ther isn't anything that would make the gear and bearing want to move upward under operating conditions but it seems a bit of an odd design to anyone used to automotive and marine gearboxes.

 

[RobJ]

Looks like they are a little bit to much on the inside looking at the wear marks.

Maybe this will help, from my L2500 manual which is probably close.

Rob

 

[VT_Kubota]

Thanks Rob, that helped. I assume by "too much on he inside" you mean they were too deep?

There was a single 2mm originally. I ended up with a .8mm on that bottom bevel gear. I'm doing the seal on the other side too and will be checking that gear also. I told the dealer if it looked like the first one, I'd be back - and looking for a bigger break on the parts!!

 

[RobJ]

From what I could tell depth was decent, but there was a lot of wear on the inside...large part of the gear and little in the small end. Even though it's a bevel gear, IMO it should still cover equally. Where your gears broke, it seems that is where most of the wear and pressure is.

Man just seems like a lit of these bevel gear systems fail when they really shouldn't.

Good Luck,
Rob

 

[rbargeron]

........ Does this gear and bearing assy just "sit" (via gravity) down against the shim(s) and snap ring in the bottom of the gearcase since there is nothing that shows any shims between the gear and the bearing??........

Yes, it just sits there. The driving force tends to push the small gear down against the bearing - no snap ring above to locate it, just shim(s) below the bearing to get the right clearance.

What condition was your 40T gear in? The damage on your 12T gear looks like a ball got loose from a bearing or part of a tooth broke out of the bigger gear. Could you tell if the hub had been apart before?

 

[VT_Kubota]

What condition was your 40T gear in? The damage on your 12T gear looks like a ball got loose from a bearing or part of a tooth broke out of the bigger gear. Could you tell if the hub had been apart before?

The 40T gear was fine; almost no wear and absolutely no damaged teeth. The bearing on the bevel gear was noisey and didn't feel good but I think that from sitting at the bottom of the housing running in oil filled with bevel gear particles. I looked closely at the bearing and didn't see any missing pieces and all the balls are in their races.

I bought the tractor brand new; it has less than 600h now and it has never been apart. This is actually the first major failure I have ever had with it. The front 4WD axel assy has been serviced by the book and I have always used 80w-90 gear oil. I know they now say either is OK but I believe gears need gear oil NOT UDT!

 

[rbargeron]

I agree about 90-weight. Man that's a real head scratcher how that 12T gear gave up so much material without the 40T showing any damage. It's possible the 12T got through-hardened instead of just case hardened - that would make the teeth brittle well-below the surface which it looks like in the pics. Backlash errors don't usually do that kind of damage - more likely to be just uneven but smooth wear along the tooth.

 

[VT_Kubota]

I agree about 90-weight. Man that's a real head scratcher how that 12T gear gave up so much material without the 40T showing any damage. It's possible the 12T got through-hardened instead of just case hardened - that would make the teeth brittle well-below the surface which it looks like in the pics. Backlash errors don't usually do that kind of damage - more likely to be just uneven but smooth wear along the tooth.

Well, here is the second part of the head scratcher puzzle:

I just came in from opening up the left side to replace that seal. Damned if the damage to that lower bevel gear wasn't identical! So I'll be headed to my dealer in the AM to get another gear and bearing. That will spoil another $100. I told them when I was ther getting the parts for the first disaster that if the damage was the same on both sides we would need to discuss whether or not they would approach Kubota about some kind of customer assistance. My feeling is that if something broke and got into the gears, it would be unlikely for it to damage both sides since any pieces would have to travel across the pumpkin in the middle which acts as a natural low point.

My instinct is that either both gears had bad heat treatment or they were set up too tight initially.

 

[rbargeron]

I agree - the gears may be a little too hard and/or they may have been installed a little too tight. It's also possible the 12T or the 40T gears didn't get all of their tooth-shaping finishing operations when they were cut (harder to prove but a good machinist can tell by examining them). Even if there's no major damage visible on the 40T gear(s) there may be some tooth crown roughness. If so it would be good to smooth it with a die grinder so the new 12T gear survives.

 

[Leejohn]

Don't over look the ID bore not being 90 degrees to the mounting flange. After you get it shimmed I would get me some blueing and check the wear pattern. Lee