Possible Air In Backhoe Dipper Stick Cylinder - Cycling Doesn't Eliminate - Help

   #1  

snymat68

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I think I have some air in the cylinder/line for my backhoe dipper stick. The dipper stick extend (cylinder retract) works fine. When pulling the dipper stick toward the tractor (cylinder extending) once the dipper stick is all the way back to the point where the welded stops should be hitting the boom, the dipper stick dangles freely like a pendulum for about 3 seconds until the (what I'm assuming is) air gets compressed. If I retract the dipper stick to the point where it can dangle freely, if I push it back and forth by hand, I get almost an inch of free movement of the cylinder rod in and out. Also, for those 3 seconds while the air is compressing, I can hear what sounds like bubbles going through the hydraulic line at that end of the cylinder.

I've cycled the hydraulics stop to stop about 20 times and zero change. There is no oil leaking out anywhere and all the fittings appear tight, so I don't think there is any air actively leaking in anywhere. Being that it's a new backhoe, I'm guessing it was just air in the line from the factory that I didn't notice at first.

My question is, how do I fix this if cycling the hydraulics doesn't work? Can you bleed tractor hydraulics like you bleed hydraulic brakes in a car? Since the pressure is higher, not sure if that would be safe or not? :confused: Suggestions?

Also, not sure if it's related, but the boom swing cylinder and/or circuit has started making a kind of squealing sound when actuating at anything less than full open on the valve. Not sure if this is normal or not. It was pretty quiet for the first 5 hrs of use, then started making the sound.

The bucket curl is about the only circuit that seems to be working properly. LOL.
 
   #2  

EddieWalker

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Air is never the problem with tractor hydraulics. It's just not an issue. Ever. It is either warn seals around the piston in the cylinder, or the control valve. Since the seals always wear out eventually and need to be replaced, that's usually where the issue is.
 
  
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#3  
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snymat68

snymat68

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Air is never the problem with tractor hydraulics. It's just not an issue. Ever. It is either warn seals around the piston in the cylinder, or the control valve. Since the seals always wear out eventually and need to be replaced, that's usually where the issue is.

This is a brand new piece of equipment. Maybe defective components? The problem seems to be on the base end of the cylinder though, where their is no seal.
 
   #4  

Gary Fowler

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I agree with Eddie, air works out of the system really fast and should not be an issue. Either the seal is damaged and leaking past or the cylinder bore at the end is scarred or out of round causing a bypass of the oil. This is a good time to call for some warranty work.
If possible go by your dealer and check out another tractor of your model and see how it operates then you can show the shop manager how is should work and maybe show a video of how yours is working.
 
  
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snymat68

snymat68

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Yeah, I'm definitely going to get the dealer involved. I've only had this thing a few weeks! Seems strange though, if it was internal scoring or something, that it would ever "tighten up" at the end of the travel. If it gets to the "loose spot" of it's travel and I hold the lever for another 3 seconds it WILL repressurize and hold tight against the boom. Also, once the hydraulics "catch up" and the cylinder starts moving again, it seems to always have full power, not reduced as if oil was somehow bypassing. Who knows.
 
   #6  

LD1

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I am gonna go a different route here and think maybe nothing is wrong? But let me ask some questions then explain my logic.

Is this doing this and/or causing a problem when actively digging?
I envision this happening when you have the dipper fully extended (cylinder retracted)....and go to crowd the dipper in some (extend cylinder), maybe half way, then stop.....now you can move the dipper back and forth by hand? Is this accurate?

If the above is true....I think its hydraulic pump capacity vs gravity.

As you are extending the cylinder (crowding the dipper in toward the tractor), gravity is making it move FASTER than your pump can get oil to the cylinder. Therefor you have air in the cylinder.

This happens and is a common complaint on front loaders. When someone has a bucket full of dirt or gravel.....dump it, then immediately want to back-drag to smooth it out. Only the bucket is no longer rigid. Some here call it "floppy bucket syndrome". Some front loaders use a regen circuit for dumping to solve this.

But the fact that you can actually see the cylinder rod move in and out of the cylinder tells me it isn't pivot pin slop, and the issue is defiantly air. I suspect what I describe is the source. But when actively digging and making the dipper encounter a little resistance, this shouldn't be a problem/
 
  
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snymat68

snymat68

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I am gonna go a different route here and think maybe nothing is wrong? But let me ask some questions then explain my logic.

Is this doing this and/or causing a problem when actively digging?
I envision this happening when you have the dipper fully extended (cylinder retracted)....and go to crowd the dipper in some (extend cylinder), maybe half way, then stop.....now you can move the dipper back and forth by hand? Is this accurate?

If the above is true....I think its hydraulic pump capacity vs gravity.

As you are extending the cylinder (crowding the dipper in toward the tractor), gravity is making it move FASTER than your pump can get oil to the cylinder. Therefor you have air in the cylinder.

This happens and is a common complaint on front loaders. When someone has a bucket full of dirt or gravel.....dump it, then immediately want to back-drag to smooth it out. Only the bucket is no longer rigid. Some here call it "floppy bucket syndrome". Some front loaders use a regen circuit for dumping to solve this.

But the fact that you can actually see the cylinder rod move in and out of the cylinder tells me it isn't pivot pin slop, and the issue is defiantly air. I suspect what I describe is the source. But when actively digging and making the dipper encounter a little resistance, this shouldn't be a problem/

That sounds pretty accurate, mostly. The "free play" occurs when the dipper points straight down to the 6 o'clock position, so that would fit exactly with your explanation.
HOWEVER, there is ALSO a pause when actively digging with the dipper. Even when the dipper has been in the dirt with resistance since the beginning of the stroke.

I'm having a guy stop out Saturday to take a look at it.
 
   #8  

LD1

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That sounds pretty accurate, mostly. The "free play" occurs when the dipper points straight down to the 6 o'clock position, so that would fit exactly with your explanation.
HOWEVER, there is ALSO a pause when actively digging with the dipper. Even when the dipper has been in the dirt with resistance since the beginning of the stroke.

I'm having a guy stop out Saturday to take a look at it.

Perhaps the dirt just wasnt offering enough resistance to slow down the stroke?? Take a bigger bite maybe;)

Let us know what you find out
 
  
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snymat68

snymat68

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Perhaps the dirt just wasnt offering enough resistance to slow down the stroke?? Take a bigger bite maybe;)

Let us know what you find out

That's a possibility. We'll see what they say.
 
  
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#10  
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snymat68

snymat68

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Monroeville, PA
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RK24H, Gravely 8123
I am gonna go a different route here and think maybe nothing is wrong? But let me ask some questions then explain my logic.

Is this doing this and/or causing a problem when actively digging?
I envision this happening when you have the dipper fully extended (cylinder retracted)....and go to crowd the dipper in some (extend cylinder), maybe half way, then stop.....now you can move the dipper back and forth by hand? Is this accurate?

If the above is true....I think its hydraulic pump capacity vs gravity.

As you are extending the cylinder (crowding the dipper in toward the tractor), gravity is making it move FASTER than your pump can get oil to the cylinder. Therefor you have air in the cylinder.

This happens and is a common complaint on front loaders. When someone has a bucket full of dirt or gravel.....dump it, then immediately want to back-drag to smooth it out. Only the bucket is no longer rigid. Some here call it "floppy bucket syndrome". Some front loaders use a regen circuit for dumping to solve this.

But the fact that you can actually see the cylinder rod move in and out of the cylinder tells me it isn't pivot pin slop, and the issue is defiantly air. I suspect what I describe is the source. But when actively digging and making the dipper encounter a little resistance, this shouldn't be a problem/

Okay. So after watching some YouTube stuff on Floppy Bucket Syndrome, you might be right. I've been doing all my backhoe work with the tractor at idle (~1400rpm) to keep the motions a little less jerky until I get a better feel for the thing. After I get home tonight I'm going to try it at a higher RPM to see if that makes a difference. If so, then I think you hit the proverbial nail on the head with the pump not keeping up and it drawing a vacuum in the cylinder. I'm also going to try smaller (not fully extended) movements of the dipper from around the 7 to 5 o'clock positions to see if that still has the issue or if it's just when "gravity wins out" and forces the dipper down from a higher position.
 
 
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