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
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
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
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
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
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
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
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
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
Good day Updated file attached for your observations. Kind regards Uffex
thank you sir for your help
ill let you know what i find but it wouldnt be before a month a least
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
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
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
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 ( P ulse W idth M odulation). Inside the actual boom spool you have a check valve, has this been removed and inspected? Kind regards Uffex
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
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
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
Good day Post the schematic so I may be sure I am not giving any bum steer. Kind regards Uffex
here are the best i could find i believe they cover the whole control block
Good day According to your information both primary & secondary valves are connected when lowering the boom. By disconnecting the pilot line to the priimary we can see what effect we have by just lowering with the secondary valve.See attached. Kind regards Uffex
ok i will check this out and see what i see
so with boom down pilot spool on boom 1 spool blocked off i can only get half the pressure i get if it isnt blocked off. i only blocked off the top since this is where boom down pilot pressure goes to .
Good day Please block of the primary in the same way lets see what happens using just the secondary. Primary Vlave No.1 Secondary No.2 Kind regards Uffex
if i block off the primary then boom down doesnt function
Good day This is proving to be tricky to solve, please check the bucket spool has no faults - loose spring - also be sure the boom secondary is good also. Kind regards Uffex
sorry for the delay here . so i pulled the spools and examined them and to my eyes they are in good shape . the springs arent broken or anything
Curious if you ever solved this issue, I’m working on a 350dlc with this exact problem
nope i never did im using it as it is