New JD 710 owner needs help. No crowd (dipperstick) power

[workshoprat92]

Right you can have pressure but no flow!!!! Again like you say under load!
The hyd system will either make full rated pressure or it wont under load. Now the pump may be flowing its ass off but your not getting full rated pressure to the function you are activating. This is because somewhere in the system it has found a path of least resistance and will take that. The total system pressure will only get as high as that path of least resistance will provide.

In all that i have read i have not seen any mention of what full rated system pressure should be or if any messurements of this pressure has been taken at the actuation point where the pressure is needed.

 

[workshoprat92]

Ok one other thing and this may be a stupid question but does your controll stick have alot of slop in them? Is there a million miles of movement before it actually starts to move the valve?

 

[workshoprat92]

Also delmar did hit on something else i agree with. The only way you could have full rated pressure and not be able to move a load that is within the mathmatical capability of that machine to move is you have to have an opposing force reducing the avalible pressure differential to move the load. Like delmar says pressure on the other side of the piston. If you have 100 psi on one side and zero on the other you have 100 working psi avalible to multiply on the square area of the cylinder. If you have 100 psi one side and 50 the other you now only have 50psi to multiply on the area of the piston.

Again you need to take the time to know what your pressures are and where. If you have a high pressure on the backside of the piston opposing sytem pressure on the front side than id start to suspect a control valve issue. Of course a restricted or crushed oil return line could cause the same effect.

 

[workshoprat92]

Something else comes to mind re reading some of the posts and the talk about destroking the pump. From what i remember i learned about that system from when i was looking at buying one the destroking function is only for destroking or unloading the pump when starting so the pump does not put an un needed added load to the starter. This is acomplished with an electrically activated valve on the pump. This valve is part of the 4-5 components you change all at once!

 

[workshoprat92]

Hey just one more as this thread is bringing up many memories about looking at this series of machine. To be very honest i have looked at well over 8 machines in the 710d. I have yet to find one that should perform the way i think it should. I had also come to the possible conclusion that the 710d really was just an under engineered dog! I have yet to find one machine or anyone who has had one say im wrong!

 

[Jay E.]

Im going to do the lift tests and have the different circuits flow tested and report back. Stand by...

 

[workshoprat92]

Sounds like a good idea. My work here is done. Good luck.

 

[Jay E.]

Here is the information from todays tests.
Concrete boxes are 2500 lbs. Measurements are from the stabilizer to the bucket teeth.

Dipperstick at 13' should lift 6250, it JUST lifted 5000
Boom at 14' should lift 3530, it could NOT lift 2500
Bucket should lift 7700, couldn't lift 5000, but it could curl it.
Curl couldn't even lift 5000, didnt try 2500 I don't know if 12500 lb breakout force is the same as lifting force.
All was done at high idle, it didn't make any difference if I ran it faster
So force was down all across the board.
I bought some 3000 lb preassure gauges today, I'm going to T them all over the place.
It is really going to **** me of if the JD tech's pressure gauge was inaccurate since all this drama was based on those readings.

In the first photo, I could extend the e stick about 2 feet before the loader bucket came off the ground. But the dipperstick couldn't lift it if I sent it out at all.

Testing dipperstick at 13'. Testing curl. Each box weighs approximately 2500 lbs +/- 100

Testing boom at 14' and 2500 lbs. It could not lift this. Should lift 3530



Testing bucket lift

 

[redneckracin]

That really makes me smile seeing the tests for some reason!

 

[Jay E.]

More testing. It appears that there is 2550 at the cylinders. Either 2550 is not enough to push the parts to their rated force (doubtful since this is the specs published and the force I have is so much lower) or somehow the spool valves/hydraulic controls/destroking function is working incorrectly and as soon as it sees 2550 it reduces the flow to an amount that simply cannot move the part. It has power, then it just stops, the stick functions (all of them) stop moving far below the ratings. This occurs whether you open the flow just a crack and let it move into the weight, or move into it full stroke. The function just stops, the stick is dead, except if you reverse it out. Even while one of them is stopped, you can still move the others, so the hydraulic pump will put out fluid. But any one of the functions, independently or in concert with others, will cease to move as soon as it gets to 2550 lbs, and on the way up to 2550 lbs it does not exert the force it should. Meaning at 2500, before it cuts off, it isn't moving 95% of its maximum strength.
I tried lowering the pressure to 2400, it still cut off exactly the same way, just lifted less. Which makes sense, once a closed loop system sees no more flow, it cuts out. BUT THERE SHOULD STILL BE FLOW BECAUSE IT SHOULD NOT BE STALLING OUT! The next step is begin cranking up the pressure and see what, if anything, that does. Hopefully it doesn't blow seals. I think the cylinders are rated for 3000 lbs. I'm thinking there needs to be a bit or reserve PSI, sort of a cushion to keep the flow going so it works at 2550? I don't know. At 100 lbs less it doesn't lift close to capacity, I cant see what 100 more PSI is going to do. All the functions are 20 to 50% low on power, curl, crowd, boom, loader.
I may get a 3000 psi electric hydraulic power pack and bypass the entire 710 hydraulic system. Put in my own valve and new hoses. Then see if the crowd or curl function will dig properly at 2550 lbs with a system that does not have a destroke closed loop system. At least then I would know the geometry and cylinders have the function and power that is advertised. That is going to be A HUGE amount of work. Perhaps I'll borrow a 410 and hook that up, even if the pressure is lower by 100 lbs. Hopefully you guys are still following this and can help me out.
I'm out of ideas. So is everyone else that has looked at it. But the answer is out there somewhere.

 

[Bls repair]

Have you checked the pressure on the return at the same time as the pressure side ?

 

[Jay E.]

I'm going to do that as soon as I get some more pressure gauges. Until it hits max pressure all the controls move freely, so I don't think it is bleeding by the piston seals. Plus it will stall in any position in the stroke. What were you thinking?

I'm still looking for someone that has a flow tester.

 

[Bls repair]

You may have something happening that is stopping or slowing return causing back pressure and locking cylinders up .
Years ago had a Ford back hoe, when you tried to curl bucket it moved about an inch and stopped.What we found was end of rod broke off in side one of the two curl pistons . When we tried to move bucket it would pressure the return side and lockup.

 

[Jay E.]

Thanks for the input. I'll be posting what the additional gauges show.

 

[Jay E.]

I received some feedback form Jerry at Kin-tec Industries. His company is very highly regarded when it comes to rebuilding the hydraulic pumps on these. He felt that there could be one or more bores of the pump that are worn and this allows the fluid to build to pressure, but not to be able to work properly. He has had others with this same problem and it was helped by a rebuild.
Basically, beyond a certain point the pump flows around the worn piston bores.
This is the second pump rebuilder that has contacted me to talk about this problem. So before I go through the work of hooking up hydraulics independently, I'm going to remove the pump and send it to Kin-tec to be tested. There wont be any posts until I have that information back.
http://kin-tecindustries.com/contact-us/

 

[workshoprat92]

I am only going to say this once and im pretty sure it is going to fall on deaf ears with a lack of understanding of science to understand what I am saying. If the system is rated to produce 2550 lbs of pressure and you are achieving 2550 lbs of pressure then the pump is putting out max rated pressure. since force is totally a function of pressure multiplied by the square area of the piston and you are producing the max system pressure then the only way that there cannot be movement. Listen carefully THE ONLY WAY THERE CANNOT BE MOVEMENT is if you have an opposing force equal or greater to the force you are using to cause movement. FLOW MEANS NOTHING other than the speed at which you will move a function within its rated pressure range given the fact that the opposing force is not greater than the force you are trying to use for movement!!!!! PERIOD!!!! You absolutely cannot max out the pressure of a function and yet have no movement as a matter of lack of flow. movement will only be created by pressure differential or difference in force vs resistance

one of two things is happening here.
#1 you ethier have an opposing force equal to or greater to the force you are trying to use such as pressure on the return side of the cylinder causing a massive reduction in the pressure differential thus reducing the force. For example if you have 2550 on the pressure side of the piston and 0 psi on the other you have a 2550psi pressure differential. Ok if you have 2550 on the pressure side of the piston and 2000psi on the return side then you only have a pressure differential of 550psi and in effect only have 550psi of force to work with. or you have a massive resistance created by the possibility of a frozen pin. highly unlikely as loose as all these used john deere machines i have looked at are.

#2 And from the many many 710 machines I have looked at that all functioned this way the conclusion that I have come to and have yet to see a 710 prove me wrong is that the 710 is an under engineered pos dog and you are getting max out of the machine and the john deere performance numbers that are advertised is totally a joke and a complete lie and fabrication or just a pipe dream!!!!! Also my brother was an engineer for john deere on thier construction equipment and he tells me that john deeres attitude is that if a machine has so much power it can drag itself into the hole like cat and every other machine i have run will do then that is not good and the machine must be derated. I belive him because all the deeres i have run are just as he described and a cat or case will eat a deere for lunch.

 

[Jay E.]

FLOW MEANS NOTHING other than the speed at which you will move a function within its rated pressure range given the fact that the opposing force is not greater than the force you are trying to use for movement!!!!!

I understand the need to talk down to me like I am an idiot. But I'm not. The problem may be that the speed of the movement is so slow that it is useless. There is some reason why the speed is so slow. I intend to find out what it is.

710 is an under engineered pos dog and you are getting max out of the machine

This is possible, but one of the neat parts of a forum is that I have been assured by several owners that the machine is a monster at trenching. The issue most have with it is that the components of the boom are very heavy, and expecting it to be nimble and work quickly is not realistic. It is not an excavator.
I have several options on how to continue to figure out what is wrong and until I satisfy myself that it is impossible to make function at a reasonable level for a modest cost, i will keep working on it. When I find the answer I will share it.

I have quite few older machines, an Allis Chalmers D45 grader, a 944 Traxcavator, an old W900 Kenworth dump truck, a DD 400 International semi, an ancient White 8 x 10 water truck, and numerous steam powered tractors. I have also restored UH-1 helicopters and radial powered aircraft. All of them were purchase non operating and all of them are used for their intended purpose all the time. The only reason that I went on this forum is because I purchased this as a working machine that I hoped to not need to spend my time fixing it. I am fully capable of fixing pretty much anything I set my mind to. I was hoping someone was going to respond with an answer based on the experience of fixing one, not telling me how NOT fix it.

What would be really helpful is if one of YOU experienced guys could come to Southern Oregon and hook up all the appropriate equipment and see the results. With any luck we won't be standing around scratching our heads like the other experienced guys wondering why it isn't responding to the inputs like it should. Until then I'll just keep trying to fix it as best I can.

 

[hosspuller]

Seems like you could answer the doubts of several posters by flowing the return of the crowd cylinder into a bucket. Then there is no hydraulic back pressure and the only restriction possibility is mechanical.

And speaking of mechanical... Any chance the crowd cylinder has been changed ? Perhaps smaller diameter ?

 

[workshoprat92]

Its hard to know the skill level of others on a forum. Wasent trying to talk down to anyone but merely emphasise the facts of the science. Sounds like you have aircraft experience like i also do. If you have an a&p like i do then you probably went through school and had some training on the subject of hydraulics. I also hold ase master heavy truck ratings as well as ase master auto ratings. Plus 25 years working on about everything you can imagine. Not trying to impress you or break my arm patting myself on the back. However one thing i have learned in all my training and experience is that it is awfully easy to get your mind locked on a thought that you cannot get rid of and clouds all other options. Most of the time on forums like this you hear lots of opinions and possibilities but no imperical data to back up anything. Such as the case in what you have put forth in testing data and what you have said the machine is doing. I also have my own experience in looking at several of these machines for possible purchase and all of them opertate just as you have described. In fact i even went to an auction in dallas that had 4 of them and they all ran the same with no difference between them and were all in my opinion hydraulically deficiet. When i ran those machines the function would flat stall. They would reach a point where there was no movement at all! And whats most puzzling is when they did this the engine would not load down like on any other machine i have ran. I have a real hard time believing that out of 6-7 machines i had looked at that they all would have the same problem. I could not find one machine that worked as advertised. If this actually is a hydraulic issue and not just a under engineered design flaw then i find it really hard to belive that this is such a common issue that 6-7 machines i looked at all have this issue and no one anywhere has seen this problem or know what causes it. No one anywhere in this huge pool of online knowledge or even dealers and shops could i find anyone thats even remotely knowedgeable about the functioning of this machine. It really is a very baffling thing all the way around and has caused me to steer way clear of this model and honestly anything deere. I really honestly wish you luck and hope you do find it. I would very much like to see one of these operate as advertised. On paper this machine should be a super beast. But yet have to see that is!!!

 

[Delmer]

When i ran those machines the function would flat stall. They would reach a point where there was no movement at all! And whats most puzzling is when they did this the engine would not load down like on any other machine i have ran.

That's exactly how they are designed to operate. Take a look at the controls, or service manual, or anything written about a closed center hydraulic system, when the function reaches the end of the stroke, or stalls, the engine DOES NOT bog down because the pump is unloaded, the pump cannot tell the difference between a stalled function and a closed valve, same pressure and same flow.

I'm glad to answer questions, or clear up confusion as I see it. But I try to follow three and out, suggest something three times with no response, or hear the same nonsense three times and I'm out.