Floppy bucket on BX 2680 or Compressible hydraulic fluid---NOT what's wrong

[robstaples]

My single cylinder bucket seems to have a loose connection between the shaft and the pressure plate , for lack of better words. The part of the cylinder that moves when oil pressure is applied.
See video and frozen frames of video in pics. My strain is lifting the weight of the bucket. It made no difference if the engine was running or not.
My dealer thought the nut may be loose and replaced the cylinder. New tractor 20 hours old.
The floppy cylinder was first noticeable when I went to back blade. But if I applied hydraulic pressure, the slack is taken up and the bucket stiffens up. My L39 does not do this. Its cylinder stays where it is left.
I thought maybe air in the line, but even air compression is more resistant than this.
I would love to see an X-ray of what is going on in the cylinder.

Two new cylinders doing the same thing.

I am interested in your thoughts of why this does this.






Floppy Bucket - YouTube

 

[Roadworthy]

Does the loader raise and lower normally when asked? Will it curl when told to? Check the position of your three point lift control, especially the rear one. That can affect bucked operation on some tractors. Other than that my guess is a problem in the control for the front loader.

 

[Stan B]

That's a pretty extreme example of something that was happening to my FEL too, and happens (based on Internet research) on many SCUTs and CUTs. When dumping the bucket, the hydraulic pump doesn't supply enough flow to fill up the head end of the cylinder, so you get an air pocket. The "fix" is to install directional flow restriction on the line from the rod end of the cylinder. This forces the hydralic pump to "work" to fill the head end of the cylinder. I just installed this fix on my Kioti CK3510 and the floppy bucket issue is gone.

This part from Surplus Center is the valve I installed on the rod-end line. It is installed so that the flow is restricted OUT of the rod end of the cylinder, and unrestricted flow IN.

 

[robstaples]

Does the loader raise and lower normally when asked? Will it curl when told to? Check the position of your three point lift control, especially the rear one. That can affect bucked operation on some tractors. Other than that my guess is a problem in the control for the front loader.

Everything else with fel works as expected. When I move the bucket ( by hand) I don’t feel oil moving or air. It’s just like loose inside

 

[robstaples]

That's a pretty extreme example of something that was happening to my FEL too, and happens (based on Internet research) on many SCUTs and CUTs. When dumping the bucket, the hydraulic pump doesn't supply enough flow to fill up the head end of the cylinder, so you get an air pocket. The "fix" is to install directional flow restriction on the line from the rod end of the cylinder. This forces the hydralic pump to "work" to fill the head end of the cylinder. I just installed this fix on my Kioti CK3510 and the floppy bucket issue is gone.

This part from Surplus Center is the valve I installed on the rod-end line. It is installed so that the flow is restricted OUT of the rod end of the cylinder, and unrestricted flow IN.

Thanks Stan, just to understand better, I noticed mine after carrying max load of gravel in bucket. But when I hand move it, is the air leaking by the o-rings? Otherwise, would I be compressing the air pocket?
Also, then it should work away with exercising an empty bucket? I’ll try that now.
With your fix, the pump has to work to dump the bucket versus just gravity?
Thanks

 

[Fallon]

One very common OEM preventative fix is regen. Apply fully hydraulic pressure to both sides of the cylinder. The increased area on the but end overpowers the rod end & it extends. The extra fluid from the rod end makes it extend faster. It trades power for speed.. The fact both sides of the cylinder are pressurized means it don't such in air through worn seals as the bucket pulls on the cylinder when dumping.

Most loader valves have recently these days. Economy Ls only have regen dump. Grand Ls have a 4 stage valve with regen as the first stage then normal power dump all the way at the end of the valve.

It works well for a bucket or forks, but can cause unexpected issues if you use a diverted. It will only angle a plow with a pair of single acting cylinders 1 way for example.

 

[Stan B]

Thanks Stan, just to understand better, I noticed mine after carrying max load of gravel in bucket. But when I hand move it, is the air leaking by the o-rings? Otherwise, would I be compressing the air pocket?
Also, then it should work away with exercising an empty bucket? I’ll try that now.
With your fix, the pump has to work to dump the bucket versus just gravity?
Thanks

If you run your tractor up to full PTO RPM, which is equivalent to max hydraulic pump flow, the cycle the dump a few times, the problem will likely go away for a bit because it chases that air pocket out of there.

You will definitely notice it more after dumping heavy loads as the load is pulling the bucket down which sucks in some air. It is exacerbated by trying to dump a heavy load gently, like metering out a bucket of crushed stone over a driveway.

Believe it or not, when you lift up on the bucket like in your video, you are actually compressing that air pocket.

When you cycle your bucket to get the air out, make sure to let the system go into relief at both extremes (curled and dumped) a few times.

 

[robstaples]

I did run the bucket to both limits and the muscle movement disappeared. Now that I understand cause and effect, I may add the restrictor valve.
I just curious why it doesn’t happen on bigger equipment. People use their equipment to its maximum capability all the time.

Maybe it does...

 

[Fallon]

I did run the bucket to both limits and the muscle movement disappeared. Now that I understand cause and effect, I may add the restrictor valve.
I just curious why it doesn’t happen on bigger equipment. People use their equipment to its maximum capability all the time.

Maybe it does...

As I noted above, the regen function on many modern loader valves prevents a floppy bucket due to air from worn seals. The L series & similar John Deere machines use regen. Id assume most of their bigger machines & most other manufacturers use it as well.

Plumbing a 3 stage valve with regen really isn't any more difficult than a normal valve. A 4 stage valve with regen & normal power dump is more material & machining so will be more expensive.

 

[LD1]

One very common OEM preventative fix is regen. Apply fully hydraulic pressure to both sides of the cylinder. The increased area on the but end overpowers the rod end & it extends. The extra fluid from the rod end makes it extend faster. It trades power for speed.. The fact both sides of the cylinder are pressurized means it don't such in air through worn seals as the bucket pulls on the cylinder when dumping.

Most loader valves have recently these days. Economy Ls only have regen dump. Grand Ls have a 4 stage valve with regen as the first stage then normal power dump all the way at the end of the valve.

It works well for a bucket or forks, but can cause unexpected issues if you use a diverted. It will only angle a plow with a pair of single acting cylinders 1 way for example.

^^ Nailed it.

Short of a mechanical fix (re-plumbing) you can simply change how you operate.

Most times people complain of "floppy bucket" is when trying to spread/grade dirt or gravel.

Get a big ole bucket load and dump it.....then immediately lower the bucket to back-drag and feather it out. Well....the result is just like you video....floppy bucket.

Because dumping that big ole bucket load allowed gravity to dump the bucket MUCH faster than the hydraulics could replenish the oil in the cylinder, resulting in an air pocket.

So when dumping a big heavy load and you want to back drag....dump the bucket ALL THE WAY, continue to hold the lever dumped, and pause for just a second. Then curl back to whatever angle you desire for back dragging