270dlc no boom down power

[jhexjd]

so on my 270dlc when i try to lift the excavator of the track on one side using only boom down it will not lift it. As soon as i activate the arm or bucket cylinder i can lift it off no problem. We rented a 210glc that had no problem lifting one track off the ground with the boom cylinder alone with no help from bucket or arm cylinder im just wondering if someone can tell me why this might be thanks

 

[uffex]

Good day
The observation you report is not so unusual, when lifting many machines' undercarriage it can stall the hydraulics. To be certain you have a fault, install a pressure gauge to the boom down line and measure what pressure you have when the cylinders stop lifting. Full relief pressure will mean that it is a geometry issue and not a hydraulic fault. Boom down issues are in most instances accompanied by a creep issue, where the cylinders will not hold the equipment up.
Hope it is of help.
Kind regards
Uffex

 

[jhexjd]

thank you for your reply sir i will check that out i do believe the cylinder drift is less than spec so im not thinking that that is the issue excavator operates fine othrwise but ill check this out

 

[jhexjd]

Good day
The observation you report is not so unusual, when lifting many machines' undercarriage it can stall the hydraulics. To be certain you have a fault, install a pressure gauge to the boom down line and measure what pressure you have when the cylinders stop lifting. Full relief pressure will mean that it is a geometry issue and not a hydraulic fault. Boom down issues are in most instances accompanied by a creep issue, where the cylinders will not hold the equipment up.
Hope it is of help.
Kind regards
Uffex

so i installed a guage to the lines that go to the top of the boom cylinder and here is what i found : when i use only the boom cylinder function to try and lift the excavator the most pressure i get is 1200 psi. when i activate the arm cylinder (i dont have to actually move the cylinder just move the joystick to the point where it almost starts moving) i can get 3000 psi max. when i do the same thing with the bucket cylinder i get 5000 psi the pressure drops gradually but the cylinder does not drift or at least very little . it seems like activating those other two cylinders lets more pressure come to the boom cylinder im not sure if this is an issue boom lifts good maybe a little slow but still lifts good let me know what you think please
thank you

 

[uffex]

Good day
From your description and checking the information we have on file, I would make the following comments. Hitachi along with most of the players use two main valves for the boom (two pumps), however when lowering the boom only one that of the Primary is activated.
During lowering (free fall) if the pressure required is less than return pressure a check valve will open allowing the return pressure to fill the negative line, the check valve is in the primary spool. I have discounted port relief valves as you do not make any observation of boom creeping and using the bucket, you achieve full pressure. If the creep prevention valve were to be taken out of the circuit, I guess you would see the boom lower of its own accord. I suspect that this valve is lodged open. My compliments on your troubleshooting to date, attached are the illustrations that may be of help.
Kind regards
Uffex

 

[jhexjd]

thank you sir for your reply i will look in to that sometime ummm i should still be able to use the excavator without causing more problems right

 

[uffex]

Good day
Not sure how or what should have been the root cause, so I cannot be sure that no other problems may arise, a temporary obstruction could become dislodged by dropping the boom from full height to the ground, but I do not endorse trying that method.
Kind regards
Uffex

 

[jhexjd]

well dropping the boom scares me a little cause it falls so fast it feels out of control but ill pop out that valve when i finish my project and see what i find thank you for your help sir

 

[uffex]

You comment the boom drops like a stone is further confirmation we are on the right track good luck and let us know how you make out, I have some information in the achieve on spool dismantling, when I get a moment I will update it and post it to you.
Kind regards
Uffex

 

[uffex]

Good day
Updated file attached for your observations.
Kind regards
Uffex

 

[jhexjd]

thank you sir for your help

 

[jhexjd]

ill let you know what i find but it wouldnt be before a month a least

 

[jhexjd]

so hopefully its not too late to start this thread up again cause im really stumped as is the mechanic i usually hire
so to refresh my problem is no boom down pressure . if i activate bucket dump or bucket load and arm out i can get lots of pressure . also not sure if this is related but my hydraulic oil runs pretty hot like 94celcius if i let it
so ive check my cylinders and they hold pressure
i plugged of the bucket pilot hoses and tried to boom down with the bucket helping and the results are the same as when i dont use bucket or arm which (correct me if im wrong) means it isnt a pilot problem
i changed the boom flow rate control valve and poppets that go with it and now my boom drifts down
i checked out the boom down spool and its all good too
im open to any and all suggestions cause this thing is bugging me and i dont know what else to check help please

 

[uffex]

Good day
First please keep in mind my information sours is predominantly Hitachi, I do not have JD 270 Hydraulic schematic. If you prefer I work from JD please suppl;y the appropriate hydrau;ic schematic.Your post specifies that boom down has only low pressure.
This only changes when you operate the bucket or arm. When I look at the schematic I cannot see any possibility of leakage into those two circuits.
I would suspect that the pump is remaining idle until you activate bucket / arm.
I would check this by comparison with arm in operation and the PWM valve output to the pump.
Kind regards
Uffex

 

[jhexjd]

thank you for the reply . im not sure i understand . arm in doesnt help to get boom down pressure. the only connection i see between the three functions is that they are beside each other in the control block with the boom 1 spool in the center between arm 1 spool and bucket spool . how likely would it be that there is a crack in the control block? pilot pressure is fine with 600 psi at the spool . when i boom down it seems i hear oil hissing at the control block . sorry for my ignorance but could you explain what the pwm valve is . also is it possible to check the pressure in neutral passages in the control block

 

[uffex]

Good day
When you activate the arm in low range and lower the boom, do you have pressure? Boom & Bucket use the same pump, if the bucket is OK the indication is that there is no passage from one to the other. PWM valves are what is controlling pump output (Pulse Width Modulation). Inside the actual boom spool you have a check valve, has this been removed and inspected?
Kind regards
Uffex

 

[jhexjd]

thank you for taking the time to reply . yes that valve was taken out and inspected there was a spring broken and replaced but it didnt change the pressure . so again sorry for my ignorance but is the pwm valve an electric valve like a solenoid and how would i check that . on the moniter in the cab i cant check any voltages

 

[uffex]

Good day
You found a broken spring in the boom primary spool. Did you get all the broken parts? Any seat damage?
If your control block was cracked fluid would leak in both directions.
My interpretation of the issue is one of two case scenarios.
1/ The pump pressure from boom down is leaking away (Hissing) operation of the bucket cylinder prevents the leakage, it could be that the pump flow increases with the bucket activation which compensates for the leaking. Can you confirm removal of the creep prevention valve allows the boom to sink to the ground? This will narrow the issue down to the actual boom circuit.
2/ The pump remains at idle when lowering the boom, one possibility not so likely is that you have a boom float system, this is a popular option in Scandinavia not so usual in Canada. It makes the hydraulic schematic relative to your machine very important.
One schematic I have shows the secondary boom valve active in boom lowering. If this is the case with your machine, we could disconnect and plug boom down pilot on the primary only use secondary to lower and see if this resolves the problem, like wise we can take out the secondary valve with the same method. See attached.
Kind regards
Uffex

 

[jhexjd]

thank you again sir for your reply . i sent the the spool to the mechanic i always hire to check and he didnt mention any other damage to the spool but he did mention that he didnt figure the broken spring would cause any problems that im experiencing . to answer your question from yesterday i dont actually have to move the arm or bucket cylinder to get more boom down pressure . i just have to move the the lever in the cab to "wake up" the engine so it revs up at which point i assume the pumps start making pressure. so although im certain that this excavator only uses boom spool one for boom down i could certainly try your last comment there. sorry for my lack of knowledge again but how would i remove the creep prevention valve i will try to post a hydraulic schematic tommorrow

 

[uffex]

Good day
Post the schematic so I may be sure I am not giving any bum steer.
Kind regards
Uffex