Broken Mount For LA724

[Ford tractor]

I was wondering HOW the OP moved the machine with the hoe. Some operators like to have the FEL bucket in the full dump position and raise the front end up a bit (some pick the wheels all the way off the ground). If he had the bucket in that position and then used the BH to pick up the rear and push the tractor to the side, all the torque would be on the parts that broke.

 

[Gizmo2]

I have to chime in here. The bottom line, IMO, is pour design and I don't care what color it is. I also don't agree with lifting the whole tractor completely off the ground by many inches while using the BH either, especially the front end. Just sayin!

 

[rswyan]

I was wondering HOW the OP moved the machine with the hoe. Some operators like to have the FEL bucket in the full dump position and raise the front end up a bit (some pick the wheels all the way off the ground). If he had the bucket in that position and then used the BH to pick up the rear and push the tractor to the side, all the torque would be on the parts that broke.

The loader bucket position was covered in the original post in this thread:

"When I use the backhoe I lay the FEL bucket flat on the ground so that it will slide when I reposition with the hoe."

So he was fine with it, in that respect .... I've done similarly once or twice myself

 

[638]

If you dig a trench between two buildings, you will end up moving the tractor off of the trench with the backhoe. That is a very common maneuver. To do that, you have to have the bucket flat on the ground to keep the front end from falling into the trench. Kubota should know how backhoes are used and should have anticipated any tractor that would accept a backhoe would be used in this way. I feel they have a design problem.

 

[amigauser]

They look like yours. Solid on the outside with a pattern cast into them on the inside. No plates welded on.

My GL3240 w/LA724 purchased the fall of 2008 also has no extra plate welded, just the castings. If Kubota made a loader mount design change it had to be over two years ago as my tractor was built in early 2008 and sat on the dealer lot for 6 months when I bought it.

 

[kcender]

My GL3240 w/LA724 purchased the fall of 2008 also has no extra plate welded, just the castings. If Kubota made a loader mount design change it had to be over two years ago as my tractor was built in early 2008 and sat on the dealer lot for 6 months when I bought it.

I don't know when they stopped putting the reinforcing plates on the brackets but I do know of one 2010 L3240 that will have the plates.That one is mine as I just finished making the template for them and will get the plates cut out tomorrow.I am thinking of 1/4 inch plate welded on both sides of the bracket.Some people will probably say that if I make that area stronger it will just break somewhere else.Maybe true but after studying this whole loader assembly,I definitely think these brackets are under built and are the weak point of the whole assembly.I am certainly not an engineer but I have worked around steel long enough to know a few things about it.I will add the plates regardless if Kubota replaces the brackets or I have to repair my own.I normally have quite a bit of faith in Kubota quality but this is one instance where I think they could have made a better product.:2cents:

 

[Baby Grand]

Kcender,

I'm currious as to what the design change was, exactly. Being a designer of castings, myself, my prime suspect is that the amount of long welds on the plate were cost prohibitive for manufacturing, and someone in a kwality circle or a cstcttng team got a paltry bonus or company coffee mug for eliminating it. My suspicion further suggests that this was accomplished by thickening the web of the casting to provide a similar dimension to that of the casting + plate.

Could you humor an obsessive design engineer and take a measurement across the thickness of your part? From the attached pictue I have a casting thickness of 7/8" with a 1/4" plate filet welded onto the web:



Thanks. Oh, happy (belated) Canada Day, by the way!

-Jim

 

[Chilly807]

Kcender,
I'm currious as to what the design change was, exactly. Being a designer of castings, myself, my prime suspect is that the amount of long welds on the plate were cost prohibitive for manufacturing, and someone in a kwality circle or a cstcttng team got a paltry bonus or company coffee mug for eliminating it.

I think you're exactly right.. the scenario was something like this..

"Ok, we had to weld stiffeners on the 724 loader brackets to keep them from cracking. Let's calculate how much more material we need to put in the mold to compensate for the lack of the stiffener plate. We'll save the cutting and welding time for the old plate and streamline the process."

Sean

 

[MHarryE]

Kcender,

I'm currious as to what the design change was, exactly. Being a designer of castings, myself, my prime suspect is that the amount of long welds on the plate were cost prohibitive for manufacturing, and someone in a kwality circle or a cstcttng team got a paltry bonus or company coffee mug for eliminating it. My suspicion further suggests that this was accomplished by thickening the web of the casting to provide a similar dimension to that of the casting + plate.

Could you humor an obsessive design engineer and take a measurement across the thickness of your part? From the attached pictue I have a casting thickness of 7/8" with a 1/4" plate filet welded onto the web:

View attachment 219894

Thanks. Oh, happy (belated) Canada Day, by the way!

-Jim

Jim - I have a LA854, not a LA724 loader, so I have a somewhat beefed up arm in the area but it is of similar design. The section is 150 mm deep by 20 mm wide or 5.9" x 0.79". Calculating the moment of intertia, it is 13.5 in^4 in the fore after direction and 0.24 in^4 in the side to side direction or 56 times stronger in the normal loader forces direction. If I am run into a bank to load my loader in float, there is no resistance from the lift cylinder so all force has to go through the main loader arm and that section has the lowest strength before it really enlarges into the torque tube weld. But it is designed to be very strong in that direction. Now visualize the bucket being firmly planted in the ground, raise the rear end and move the tractor with a backhoe bucket. If you scoot the tractor fore and aft it should be the same load as running the bucket into a bank or back dragging = no problem, working against the strong section. Now visualize pulling it side to side. If the bucket sticks for some reason it can put a high side load into the arms and that rear web is the most highly stressed point. If you go back to the first post in this thread and look at the cracked side, you can see the crack starting from the outside and actually being a vee shape. That matches the rusty area on the fracture surface of the broken side. If you anchor the bucket and try twisting the tractor in the loader frame, you end up with the loading that creates this stress. So I look at the failure and think I understand the load condition that caused it, but I have no clue as to whether Kubota should have designed it to be strong enough to withstand all the twisting load possible by pulling the tractor sideways with an anchored bucket (not that the operator intentionally put the bucket in a hole that effectively anchored the bucket against twisting load, but if it happened). Somewhere they had to draw the line or the loader would get so heavy and expensive we would never buy the product. The section needed to make that arm as strong side to side as it is fore and aft is 3.6" x 3.6" (that give a moment of 14 in^4 in both directions). Bottom line for me is I am even more glad I bought a mini-excavator instead of waiting for my Kubota dealer to find me a backhoe attachment.

 

[kcender]

Kcender,

I'm currious as to what the design change was, exactly. Being a designer of castings, myself, my prime suspect is that the amount of long welds on the plate were cost prohibitive for manufacturing, and someone in a kwality circle or a cstcttng team got a paltry bonus or company coffee mug for eliminating it. My suspicion further suggests that this was accomplished by thickening the web of the casting to provide a similar dimension to that of the casting + plate.

Could you humor an obsessive design engineer and take a measurement across the thickness of your part? From the attached pictue I have a casting thickness of 7/8" with a 1/4" plate filet welded onto the web:

View attachment 219894

Thanks. Oh, happy (belated) Canada Day, by the way!

-Jim

I just measured my bracket in the same spot as you show,it is also 7/8".From what I can see from your photos the web pattern from the casting is different on mine.Where yours is showing three depressions across the width
of the bracket,mine only has two.The third area is full thickness from top down quite a distance.It appears there was a slight change in the casting process to compensate for the lack of a welded reinforcing plate.Whether this is good or bad is debatable,I personally would prefer to see the casting process removed entirely from the fabrication of these brackets but I assume it is due to cost efficiency.I have added a couple of photos to help clarify.One shows the pattern of the webbing with the plates laying beside it that I have made to reinforce the bracket.The other shows how the plate will fit on the webbing side,it will be the same on the other side.I plan to reinforce the other bracket the same.