Guys, I have a 312A with 12500hrs. Long story short I've been told the pump is leaking internally, has been set to stroke 100% and I'm told is down on presure a little. All this from the local Cat agent. The machine has resently started tracking off line and with very little power on the left side going frontwards indicating to me a problem on the left side, and tracking right when going backwards indicating a problem on the right side to my way of thinking. I presure tested the pump, and both pumps have identical readings, 3800 psi when end stroking a ram and 4300 psi with a block in the tracks. These were maximum reading and it took less than 2 seconds to reach full presure. We then took off the case drains and with the tracks still blocked we would get about a table spoon of oil squirt out when presure was applied but nothing at all after that, again this was the same of both sides. After some head scratching we identified and removed the return line of a weak performing direction, again we got a tablespoon oil out and then nothing else. We tracked that hose back to the valve bank and removed it there, things really started to get messy here because I didn't have an end cap for the valve block but there was oil definitly a flow coming out of the return line. Unfortunally the transporter arrived then and the digger has been working ever since and driving me up the wall. I am far from and expert but I'm think I have a swivel joint problem. Is there a more conclisive test? Could the problem be somewhere else? Do these machines have a knowen problem? I appricate any information you guys can offer.
Reseal the swivel, it's cheap and easy and it seems you have the symptoms of bad seals.
More than likely yes, your seals are bad and the oil is bypassing back to the tank. Now when you said you were measuring the case drain at the pumps, do you mean the individual drive motors for the tracks, or do you mean the hydraulic pumps? I think for case drain you're allowed no more than a gallon of oil to drain out in a minute. You should also do the case drain test coming out of the top of the swivel. We had a 330B go through 2 swing motors within a month because the seals had gone bad in the swivel and would build up too much back pressure on the case drain side and just detonate the swing motor.
Remove and inspect return filter, u should find pieces of old seals in housing, last one I resealed was only around 100.00 for the seals. Couple hours and your done. Make sure to change case drain filter.
could it be ur track motor we have a 312a with about 10,000 and the motors are gone very week.
I have rebuilt many more swivels in higher hour cats than drives. Swing upper wile traveling and travel usualy gets eratic not only weak.from 375's to 120's. Proper diag is always the cheapest starting point !
At the drive motors, and then on the top of the swivel joint, exactly the same results. The A series is getting old now, but resently I've driven the latest hitachi offering and while more comfortable couldn't move as much dirt at the old CAT, might have to give it a birthday and keep it going for a couple more years.... Thanks for you advice
Thanks for all your help guys, when I get the machine back to the workshop I'll reseal the swivel joint and hope that fixed it.
Thanks again guys, that fixed the problem 100%
I’m having a swing problem on my cat E120b and what your saying here might pertain to me. I get a good bang once and a while actually more and more. Ill swing one way go to swing the other way and bang like the swing break is sticking or something. Desperately want it to be a rotary union or what ever it called. I have no book for this machine and definitely not up on excavator hydraulic systems. Any help would be greatly appreciated.
The center passage or swivel joint transfers the oil from the house to the car body for your travel motors, I think you should look at your swing gearbox and or motor. Good luck.
When the "bang" occurs, does it stop the swing as well? No funny stuff in the swing drive oil? Might want to make sure you have good power to the swing brake solenoid, when that isn't energized the swing brake activates
Why would you go through swing motors if your swivel seals were bad? Are referring to the swivel bypassing from pressure side to drain side and pressuring up the drain side thus back to the swing motor? Just seems odd.
Since the drive motor case drain and the swing motor case drain tee at the top of the swing motor, drive oil pressure can get into the swing motor when the swivel joint leaks to much. At best blowing out the swing motor seal or at worst busting the housing.
No, it doesn't stop the swing. It happens when I start the swing or when I'm at low idle and try to swing in witch case it will keep banging like a heavy chater. It dosn't do it all the time mostly after running for a while.
I mean at idle or low throttle it will continue to bang or chatter at full throttle hot it will bang at the beging of a swing sometimes almost like its sticking.
Could be the seals on the swing brake piston that is bad so it isn't able to release properly. It can be tested for leaks if you connect a porta power pump or something similar to it and pump up about 500psi, it should hold the pressure for a while without problems. It might even leak so much that you can see the pilot pressure go down when trying to swing at idle.
Where could I make that connection? I don't have a repair manual so I'm a little in the dark on locations and termonoligys. Ive been a mechanic my hole life, cars first then fuel cell fuel processing systems R&D fabrication and now industrial equipment and some machining, but never a hyraulic system of this complexity. Do mean like a regular old portapower that has all the jacking accessories? Use that with an in line gauge? Any details I would really appreciate it big time. Thanks again.
In the pump compartment you have a small valveblock with an accumulator on one end, that's the pilot oil accumulator. On that block you have 5 solenoids and the third one from the acc is the one that controls the swing brake, it is energized when performing a swing. From that a hose goes to the swing motor housing to a port that's on the lower part of the motor housing just below the 2 bigger ports, put a tee and a gauge capable of atleast 600 psi on that hose and check the pressure when doing a swing, it should be 500-550 psi when the brake is released.
This might be of some good to you