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

[Jay E.]

I'm new to this forum and to this machine. All functions work well but the dipperstick has very little power. Meaning it will move with no load and the engine pulls down slightly when it does. But but when I have even a half a bucket it will not crowd, even in loose soil. I have checked pressure at the cylinder and it is 2550 lbs. The engine rpm does not pull down at all. It is as though all the pressure is somehow bypassing actually pushing the load. How is this possible? There are no leaks in the cylinder.
As an aside, when I try to use the crowd function, the curl function power also is greatly reduced. Meaning anytime I am curling the buckat and try to crowd, the bucket curl stops until I let go of the crowd.
Machine has 5300 hours. I had dealer come out, they checked pressure at pump, control valves and cylinder. We changed the filter, it was clean. It is driving me crazy as this is a nice machine, but I cant do squat with it.

 

[redneckracin]

could it be a bad seal in the cylinder?

 

[Delmer]

So what did the dealer think was wrong? since they did the testing. Did you have the line at the cylinder dead ended to the gauge, or teed into the gauge? Neither way is making a lot of sense to me but it would help to know. Also, how does the stick extend function work?

Do you know how a closed center hydraulic system works? when a function is stalled the pump acts just like the valve is closed. The pump only loads the engine when oil is flowing.

 

[Jay E.]

could it be a bad seal in the cylinder?

The dealer says he didn't think so because the wiper seal would probably be leaking.

or teed into the gauge

it was teed in to the gauge

Do you know how a closed center hydraulic system works

No I didn't but now I do. That makes sense and this one is certainly doing that. Whether I move the stick 1/8 or the whole travel, it has the same power. It isnt pushing or pulling with any strength.

So what did the dealer think was wrong?

Here is the rub. He says that the 1999 machine is too old and that no-one at their shop has worked on 710's. After he went to the JD online help and found nothing beyond what he tried, he had no further suggestions.
I did talk to an old timer at a private repair shop and he though it might be the spool valve in the dipperstick control valve just bypassing all the fluid. A big job to repair and they are not rebuildable and no individual valves are available new. Used I can only find a very expensive complete used 6 valve set.

Also, how does the stick extend function work?

The e stick works fine, I tried moving it to see if it was hanging up something but it made no difference.

Thank you for helping

 

[Delmer]

E stick? do you mean you have an extendahoe? I meant does the stick go back out with normal power when the crowd cylinder retracts?

 

[Jay E.]

do you mean you have an extendahoe? I meant does the stick go back out with normal power when the crowd cylinder retracts?

Yes it has extendahoe. I will check extendahoe when I crowd.

 

[Delmer]

The dealer says he didn't think so because the wiper seal would probably be leaking.



It isnt pushing or pulling with any strength.

So you do mean the dipper has no power either way. And the dealer who is incapable of fixing one of the simplest hydraulic systems doesn't think a piston seal can leak without the gland seal leaking.

" Meaning it will move with no load and the engine pulls down slightly when it does."

Good, the oil moving is loading the engine.

"But but when I have even a half a bucket it will not crowd, even in loose soil. I have checked pressure at the cylinder and it is 2550 lbs. The engine rpm does not pull down at all. It is as though all the pressure is somehow bypassing actually pushing the load. How is this possible? There are no leaks in the cylinder".

No oil moving, no loading the engine, the pressure is fine. I'm inclined to think you are taking too big of bites?


"As an aside, when I try to use the crowd function, the curl function power also is greatly reduced. Meaning anytime I am curling the buckat and try to crowd, the bucket curl stops until I let go of the crowd."

Then this is definitely wrong. With the stick stalled you should be able to hold the lever back and operate the curl the same as if the stick were centered, no operation of the stick.

So based on that contradictory reasoning, I have no idea what's going on. Further diagnostic steps would be to swap the hoses and see if the problem moves to the curl or stays with the stick cylinder. Or starting with a cold machine, hold the stick stalled for 10 seconds, hop down and see if the valve section or the cylinder where the piston is are warm to the touch. If you can't find any warm spot, try it for 20 seconds.

Don't bother with the extendahoe, I think I understand the problem. Did the "tech" check the charge pressure, or the transmission screen?

 

[Jay E.]

So you do mean the dipper has no power either way.

Yes, there is no power either way.

doesn't think a piston seal can leak without the gland seal leaking

Apparently, but you have me questioning that!

swap the hoses and see if the problem moves to the curl

That is a REALLY good idea, sheesh

If you can't find any warm spot, try it for 20 seconds

Ok I'll do that. Stupid question alert... Should the oil should be warm first? Or will it get warm to the touch even with cold oil? If so, would stalling( or moving) the front bucket warm the oil?

Did the "tech" check the charge pressure,

I dont know what this is, but he only checked the pressures I mentioned above. Is the charge pressure coming into the main hyd pump from the charge pump?

or the transmission screen?

Funny you should ask this. No he did not check anything to do with the transmission. Should I do this? Can you explain the thought process here? The machines automatic seems to shift well, but it feels like the engine is not getting proper fuel as it will not rev to the limiter on a smooth road (it will in neuteral when I'm running the backhoe) except in 1st or 2nd. It bogs down in 3rd at 2000 and 4th at 1500 rpm. I'm installing a new lift pump today as the fuel output from a clean filter seems really weak. I'm not sure if low engine power is contributing to the Hyd isue, but it seems best to fix that first and then keep moving on the Hyd. Are you suggesting I clean the tranny screen too?

Thank you for your ideas and suggestions.

"Tech" was there for 5 hours and when the bill hit a grand I had enough. He said I should have it brought to his shop and expect to spend 4-5 grand to diagnose and fix what ever it is.

 

[Delmer]

You do have 8 forward speeds right? bogging in 3rd The lift pump is probably cheap, at least compared to the tech, so it can't hurt. They typically leak, not get weak, but you could have gunk in the valves making it weak. When it doesn't help, check the screen in the tank. Does the lift pump priming lever seem to have decent resistance? it shouldn't, it should pump fairly easily. You can try removing the hoses and using the priming lever with temporary hoses in a can of fuel to get a feel for what it feels like when there is no restriction on the inlet or outlet, then use your finger to plug each and compare. When it's pulling a vacuum, the lever gets harder to operate.

I might be off on the transmission. Some JD had the transmission supply the charge pressure oil to the hydraulic pump, and the charge pressure was third in line for priority if anything's left over. Too bad Lantraxco's not around here anymore, he was good at remembering which model did what. Do you have a separate charge pump on the front of the engine? An Operation and Test Technical Manual is priceless in this situation, if we don't figure this out easily.

If you wait for the perfect crisp frosty morning, I'd bet you could make it "steam" from the affected spot with the sunrise in the background. A thermal imaging camera would find it at whatever temp, or a infrared thermometer if you have the patience. I thought cold because you can feel the difference between 50 and 150 much more quickly than the difference between 150 and 250. Even a heavy dew might make it visible, I was only half kidding.

Stalling a function will not heat the oil, it just sits there the same as with the valves closed, the book procedure for warming the oil for testing purposes is to loop a hose back so you BYPASS a cylinder and activate that function, high flow low resistance makes more heat than working it "heavy".

 

[Jay E.]

You do have 8 forward speeds right?

This is a 710D and has an automatic transmission, 4 speeds on the column shift.

Does the lift pump priming lever seem to have decent resistance

The lever does not pump any fuel at all.

Its going to take me a while to make up hoses to swap curl and crowd. I am not certain if both circuits are closed loop, I have to check on that.

 

[Delmer]

Oh, I was thinking of a different transmission, third bogging is still a little odd, does it blow some black smoke when it bogs?

You don't have to swap both, if you hook up the crowd cylinder to the bucket curl hoses you can tell if the cylinder is leaking. They're all closed center valves, the worst you can do is leak some fluid, wait, no, don't block off the rod side of a cylinder, that could blow up. It looks like you might be able to switch the hoses at the valves easier than most backhoes too. Especially if you can get ahold of some good crowfoot wrenches in the right sizes. Label them first of course.

I'd still investigate the transfer pump, see if it will pump from a can, blow it out with air, or a garden hose, you won't hurt it if it's already broke. I like to see how things broke so I'd pull it apart if all else fails.

 

[house cat]

If the rest of the hyd systems work ok and you have that kinda pressure at the cylinder it's leaking past the gland seal most likely, i have seen cylinders so bad that they would stall out and not leak around wiper seals, matter of fact just replaced boom cylinder because of that problem it fixed it and it was only leaking a couple of drops around wiper seal, worth a shot.

 

[Ronsii]

Another simple test is dig the bucket into the ground a bit with the stick as straight as possible then with the wheels on the ground at a low idle in first gear will it move the stick at all and if so how much going both forward and reverse. You can also just fasten the bucket to something immovable but depending on what you see the cylinder and rod doing can tell you a lot.

One other thing nobody has mentioned is are you sure the boom/stick pin isn't seized... haven't seen it happen on a 710 but have seen it on other stuff.

 

[Bls repair]

Does the stick drift down if you raise boom and push stick out level to the ground and leave there?

 

[Delmer]

Another option, bury the bucket so the stick won't move. Remove the rod side hose and cap the HOSE. Start it back up and try to crowd the stick, if oil continues to leak then the piston seals are leaking. It will shoot some oil as it takes up the slack, but should hold after that as long as the cylinder doesn't move.

 

[Jay E.]

Thanks for the replies. We have determined it is NOT bad cylinders. Curl and crowd are bith no good, so swapping them makes no difference.

I'm going to restate with the direction we are now looking.

I have a 1999 John Deere 710D with ( im pretty sure ) closed center control valves. It appears to be a radial type of pump, the pistons are just touching until the system senses the load and the piston stroke is fully activated.

I'm not sure if it has a sequence valve (I assume it does) , but it also has a electric solenoid to destroke the pump when the engine is starting and there is no pressure.

The problem is I have 2550 lbs inline pressure on a gauge at the cylinder for the curl and crowd (and hydraulic valve port) but there is simply no POWER. It barely digs or crowds (500 lbs) , but it should be a monster, with 9500 lbs crowd force. As I move the sticks I can briefly hear the engine slightly load, but suddenly unloads when I need it to dig and wont crowd or curl anymore and the engine has no load. I don't feel or hear any bypass at my feet. At this point the cylinder pressure is 2550 lbs on an inline gauge. So it is though the pump senses the 2550 lbs and thinks it should destroke the pistons and stops pumping but still just keeps the minimal destroked pressure?? Even when I bring another valve like the boom ( which does have some power, but I cant tell if it is a lot or a bit because I cant dig enough with the curl and crowd to make a trench) !to require fluid flow, this flow does not activate any more power to the RH stick as I thought it might if the pump had destroked. As long as there is no load, the stick functions work as normal, but as soon as I need digging force the cylinders stall and the engine unloads.

I unhooked the start electric destroke to assure it wasn't kicking in, but it made no difference.

Could the pump just be worn out and when the sequence valve kicks in, it activates the full strokes and 2550 lbs but with a bunch of leakage at the excentric center it just doesnt send any power to the cylinders?

I've brought out several different JD repair people and there just isn't some obvious solution. We are still trying though. They all agree there is simply no digging force. Hopefully someone out there HAS a 710D or worked on one with this problem or I think I am screw$d.

 

[Bls repair]

Have you done a flow test to see if you may have a restriction in the return ,or lack of flow from pressure side?

 

[Delmer]

Yeah, this is weird and getting weirder.

What's the history of this? how long have you owned it, how long has it done this, did the curl change or did you not notice it originally? Also, did you swap them? Does the loader work right?

 

[Jay E.]

Have you done a flow test

Flow test is in the works. Hopefully it shows something. What should I be looking for?

How long have you owned it, how long has it done this, did the curl change or did you not notice it originally? Also, did you swap them? Does the loader work right?

I recently bought it on the assertions of a respected dealer that everything functioned correctly. I was not able to personally test run it before it was delivered. The very first time I ran it ( curl and crowd) I knew there was a serious problem. I use a 410B and know the 710 should outperform it ( at least on specs). The 710 has less power than my Kubota! Swapping hoses wont show anything as they are both weak. I have lifted buckets of loose soil with the front end and it seemed to do OK for that, but I haven't put it into compacted soil to see how it digs or lifted concrete or rocks or anything really heavy yet. I need the backhoe to work to really put the loader to work. We bought it for the backhoes power to break shale with a bigger bucket. It wont even scrape 4 inches deep with a 18" bucket. The 410 has no problem filling a 24" bucket. Pathetic.

 

[Delmer]

Before a flow test, I'd do the tests in #7, #9, #15. Force is pressure (which you HAVE???) flow is speed which you can measure by extending all the way out and bringing all the way back in, boom, stick and bucket from out to curled in. I'm thinking like 12 seconds, but see if you can find that spec. Does the boom, stabilizers and loader bucket each lift the machine on their own?

"As I move the sticks I can briefly hear the engine slightly load, but suddenly unloads when I need it to dig and wont crowd or curl anymore and the engine has no load. I don't feel or hear any bypass at my feet. At this point the cylinder pressure is 2550 lbs on an inline gauge. So it is though the pump senses the 2550 lbs and thinks it should destroke the pistons and stops pumping but still just keeps the minimal destroked pressure?? Even when I bring another valve like the boom ( which does have some power, but I cant tell if it is a lot or a bit because I cant dig enough with the curl and crowd to make a trench) !to require fluid flow, this flow does not activate any more power to the RH stick as I thought it might if the pump had destroked. As long as there is no load, the stick functions work as normal, but as soon as I need digging force the cylinders stall and the engine unloads."

This is all exactly as it should function at full pressure. You have full pressure measured at the cylinders, either the cylinders are leaking (which would heat up that spot fast, and load the engine), or there is huge backpressure on the other end of the cylinder (you can measure that easy enough), there is NO other possibility (well, the siezed pin, but you'd hear that squeeling right). It might not be up to your expectations.