Broken Lift Arm - Fix or Replace?

[J_J]

Perhaps we should start a list of any one that has welded or replaced the roll over assembly.

Some of these problems are caused by over working the machine. For instance, when the PT pucker occurs, do you realize that you are lifting about 1000 lbs behind the front wheels. The 425 weighs 1375 lbs, but several hundred are forward of the front wheel. When you are trying to lift that large bolder or large bucket with what ever, you could be putting stress on that roll-over assembly. You do that enough times, and you will get stress cracks, which will lead to failure of the roll-over assembly. Whether you realize it or not, there is this thing called reverse pressure. That is when the material you are trying to work with, overloads the hydraulics by putting more pressure on the circuit than you are generating. I have watched the lift and tilt cylinders work against each other, and I try and avoid this situation. Some thing will burst or bend. I have some flat spots in the round tubes that connect the two lift arms together. I believe this was caused by undue force, which means going beyond acceptable limits. My roll-over assembly did not crack, but the pin and tube bonded together so hard, that it would not move. We may think that our machines are invincible, but they are not. Tuff enough, yes.

 

[stray]

I may have over stressed my machine by doing this but one way or the other whatever I have to do (redesign, reinforce or repair) it must perform this Job. I moved a lot of moss before the roll-over assembly gave way so maybe I’m not asking too much of it. My first hint of something wrong when this weld cracked was a squawking sound while rolling the rake back to me. If I had kept working after this warning my repairs may have taken much longer.

 

[catsco]

</font><font color="blue" class="small">( I want to repeat PJ's question above...

For those who've experienced this problem, have you been using a mini-hoe?

)</font>

Yes, I have been using the mini-hoe. The first crack did not appear until one year and about 275 hrs.

Mini-hoe work was in the first 100 hours, then light 4 in 1 bucket digging and snow plowing with the PT blade for the next 175 hours.

Cracks were already there at that time, and I had them welded on three different occasions.

More mini-hoe work enlarged the cracks. Once the pin starts to bend, the rollover assembly is doomed, as rotating the part on a bent shaft will continue to brake the welds.

Possibly the thicker new 'tube' will prevent this from occurring again.

When using the bucket, I've only lifted the rear wheels 2 or 3 times when digging.

What do you guys recommend for avoiding overstressing lift arm parts? I had assumed that the relief valves would prevent damage.

Apparently not.

Thanks!

Mark H.

 

[MossRoad]

That's one of the things about a PT... the hydraulics are stronger than the unit is heavy... meaning it is strong enough to damage itself eventually. I've never kicked in the reliefs when lifting anything... the rear tires will always come off the ground first.

 

[KentT]

</font><font color="blue" class="small">( I've never kicked in the reliefs when lifting anything... the rear tires will always come off the ground first. )</font>

I loaded my tires and put wheel weights on the rear, trying to see if the lift arm hydraulics would bypass...

Nope...

I've since taken the wheel weights off....

 

[J_J]

I installed a quick disconnect for a plug in gage on the lift cylinders. It will indicate operating pressure, and you can also see large spikes when grabbing hold of a heavy load. You can install these disconnects through out you system and monitor the pressures.

 

[J_J]

I also took out my relief valves and sent them back to PT for testing. You could install adjustable relief valves in place of the fixed ones in the system . Apparently someone has messed up on the computations for the load limits and the relief setting. If you could prove this, PT should have to fix the components that fail in that circuit. If that 425 is rated for 800 lbs, and you can lift up 1000 lbs, and the relief does not relieve, that should tell you something.

 

[tlb]

I don't own a minihoe. Most of my use is with the LMB , followed by the SMB, then forks. I pick up some heavy rocks and tree stumps though.
-Tim

 

[toy]

At Tazwell when I took mine back to get the rollover pin fixed they asked if I was jamming it into the material to be loaded, but I hadn't done this and when they looked at it they saw that it was the fault of their weld. I asked if using the backhoe would cause this to happen and they didn't seem to think so but I would say that if when you are digging using the endloader bucket and you get one side under a big rock that you can't lifk but you continue to try lifting with only one side of the bucket I beleive that this would put a twisting strain on the loader arms and probably causing it to break. That is just a thought of what could be causing it.

 

[J_J]

I agree. Perhaps some additional reinforcement is required to stiffen the lift arms. I would think two 1/4 thick walled box tubing welded in between the lift arms would work.

Another problem I just thought of is this. If one of the lift cylinders is weaker than the other, Perhaps leaking internally, the stronger cylinder would lift first, thereby distorting the lift arms. Enough of this, will produce cracks or bind the roll over assembly

 

[tlb]

Found a good welder today and took the beast to his shop. I told him I wanted to reinforce the tilt arm (see the attachment). He talked me into a different method, one he felt was better. However, when he was measuring the clearance for the brace he did not realize the lift arms can go below grade and pick the tractor off the ground. Needless to say the first time I tried to move the lift arms all the way down it bent the arm that tilts the quick attach plate. Lucky it hit this before the lift cylinder! So back to the shop I go!
-Tim

 

[tlb]

What I really wanted was this. Anyone care to comment on whether this flange welded on the pivot arm would be effective? The welder did not think so.
-Tim

 

[stray]

Wow I don't think the welder understood the problem. Those brackets added won't hurt any thing but I would just add something like yours as well. Tomorrow I will try to illustrate what I plan to do if I have more trouble with this.

 

[catsco]

</font><font color="blue" class="small">( What I really wanted was this. Anyone care to comment on whether this flange welded on the pivot arm would be effective? The welder did not think so.
-Tim )</font>

The flanges would add some stiffness, but the bending force on the shaft is 90 degrees from where you show those stiffeners.

There is very little space to add a stiffener along that axis, but a little bit goes a long way decreasing the bending and subsequent failure of the assembly. The new rollover assembly I had welded in had a tube wall that was thicker to counteract the bending that is perpendicular to the arms of the rotating part of the rollover.

Mark H.

 

[stray]

With a configuration like this made of ¼” metal on this side and the side opposite, you should never have trouble with this pipe breaking again. The arrows indicate where welds should be. This shows 3 individual pieces. Altogether 6 will be needed the other 3 of course for the other side. Anyway this is what I plan to do if another failure occurs.

 

[J_J]

The center bar can not be there, the tilt shaft has to lie in between the tilt arms. Look at earlier pictures. His tilt arm is different. His tilt arm has two cross tubes welded in.

 

[stray]

JJ I guess my drawing wasn’t very clear. The new repair center pieces should lay here and the opposite side. The tilt bar or cylinder ram doesn’t come close. If this is what you mean?

 

[J_J]

Thanks, that picture shows more detail. I think I would do both vertical and horizontal bracing.

To those that have bent the tilt arm and pin, is the bend perpendicular to the tilt arms, or vertical to the tilt arm? It would be interesting to know where the force is coming from to bend a 2 in steel pin , inside of a 3/8 thick tube. How ever, 5000 lbs of force pushing on the center of a mass that is approximately 24 in wide gives one thought.

 

[J_J]

Your bracing idea looks good, but I would also beef up the vertical plane. A 6 in triangle,using 1/2 in steel on the outside of the tilt arms, top and bottom. Across the length, I would use 1 in wide steel, 1/2 in thick. I believe most of the flexing is coming from the center of the tilt arm, which is used as a fulcrum. Are the holes in your tilt arm equal from the center? If they are, it is set up for the bottom of the tilt arm which is attached to the cylinder to apply the same force to the top of the tilt arm, and then down through the tilt bar to the quick-attach. I believe that some of the tilt arms are unequal.

 

[stray]

Goodness JJ between you, me and the rest of us how much is this modification going to weigh? LOL /forums/images/graemlins/tongue.gif