I have a CAT 312 excavator with an unsual track problem. I have found this is a gray market machine which means getting correct manual information can be challenging. My local CAT dealer has been a lot help but is running out of ideas. From the time the machine is started to the time it is shut off the right track is hesitant to move when control lever is pushed. Meaning it takes 3-5 seconds before the track will engage to move and direction doesn't matter either. Pilot pressures have been checked at both the manifold and at the main control valve and are within spec at 500psi. Pump pressures have been checked and are also within spec. There is no power problem with any of the hyrualic functions. The swivel has been resealed already as that was the first thing my dealer told me to look at. I also swapped the hoses and now can make it so the left track has the delay in it. I removed the spool out of the right valve travel and found no scoring on the shaft or the cylinder. I also removed the spool from the straight travel and found no scoring. This non-travel happens eveytime I run the machine and then try to move. If I let off the travel levers to stop and then move agian there is no delay. Its only after running the arm has occured. I have found if I curl or open the bucket against the relief I can move instantly as the pump has spooled up to provide pressure. There is no leaks, the system is full of oil, and it has new filters.
From what it sounds like the pump does not have much of any standby pressure and has problem stroking to the load. If this is a solenoid controlled pump I would swap the two from side to side. Good troubleshooting otherwise, you have nailed it to the pump or valving. Did they flow test the unit or just pressure
Standby pressure is the same on both pumps. I have to assume that the pump is good as the pressures are the same. The only solenoids I see are the ones on the pilot manifold. There is definatley not a problem with power in this machine it's just a lazy track and only after the boom and bucket functions have been run. The delay seems to me to be almost as if the oil isn't there to go to the drive motor. With the right side picked up you can see the track try to move as if the brakes are on. Remeber this happened when the hoses were switched to th eleft side so its not a motor.
Bill, I'll share an experience I had with my 312, for whatever it is worth. I had to replace the proportional reducing valve solenoid (which I believe controls the stroke of the pump). After I replaced it, the machine would function almost normally except that the hydraulics would have dead spots, so to speak. I could try to swing but have no reaction, until I activated another function. I have learned (thanks to this forum) that certain computer calibration steps have to occur after certain repairs or modifications are made. I have yet to do it to see if it cures the problem. Think about your problem as being potentially computer related. Good luck.
as you switch the hose on the pump and the problem go to the other side I would expect that its either in the pump or the LS (load sensing) signal is not ok. need to do a pump flow test. Try to change the hose of the travel pedal block valve under the cab, you will see if the pilot signal (even if pilot pressure is in the spec dosen't mean the spool stroke enough). Did your dealer check the PRV set up? And also I will check the other action that is related with the same pump and make all the cycle cylinder test, its easy to make. Start with the travel spool block lever.
I have read on other sites about the proportional reducing valve being bad. But I would think if it was that it would affect the other functions as well. What was your original problem that you changed out the valve?
does the machine have a back-up switch? that should rule out most of the electrical side of things.... what model 312/serial number is it?
I will have to look to see if it has a back-up switch. Serial #: 6LK01962 PIN #: 7DK01652
Where specifically did you make the hose switch? Pilot hoses, or main hoses? before or after the swivel? One old trick is to take the pilot line off the top of the travel spool cap, plug the hose and leave the fitting open with a drinking straw in it so you can watch the straw to see if the spool moves with any delay when the pilot control is activated. (I'm not sure if that will be F or R, but no matter seeing as you have the issue both ways) If no delay in spool reaction then I would like to watch the two NFC pressures when you have the issue to see if they drop off at the same rate. I'm a little confused about the LS comments - a 312 is not load sensing. and there's nothing electrical could make it weak on one track. However, when the delay happens, is there any delay in the travel alarm coming on? That would be valuable info. If the straight travel spool was shifting slightly when it shouldn't, (and it shouldn't when you only travel straight, ironically) it could cause 1 track to hesitate slightly. The straight tvl spool should only shift when both tracks PLUS at least one implement are used simultaneously. - then it rearranges which pump feeds what circuit. A bit of leakage in the pilot logic network has been known to cause that straight travel spool to move ever so slightly when not called for on some machines.
PRV can be adjust with the dash. Almost of time when a bad PRV seting in the dash or bad PRV is in trouble it makes the engine to died when you open a spool. too much load on engine and just died. But the other can occur too. Not enough load on engine because an implement is consuming too much oil and the prv setting is no well set. Example if the travel motor consume more oil than the other side with a bad prv it will not stroke the pump at its best. When you said you swap the hose, did you swap the hose from the pump or the swivel/control valve area?
The hose swap was done at the top of the swivel. The engine does not change when the spool is activated. We lifted the machine up with the boom to watch to see what happens when the foot pedal is moved. The track chucks a bit but doesn't move then suddenly it will go in about 3-5 seconds. I have resealed the swivel as it was the first thing the local dealer said to rebuild. We found a couple of seals with some nicks in them but nothing out of the ordinary.
ok, so you have eliminated the swivel, the motor and the brake, final drive too. Good troubleshooting. I would be going to the straw on the spool trick next. You need to see if the two spools shift at the same time or not. If you can't repeat the symptom whilst doing the straw trick, an issue could exist in the travel pedal pilot valve. Not only does pilot pressure have to push on one side of a spool valve to move it, but the opposite hose has to drain. When you step on that travel pedal, you feed one hose and the other needs to push an ounce or so of oil out (so the spool isn't hydraulically locked), through the pilot valve back to tank. Keep that in mind.
and by back to tank, I mean right to tank - pump suction usually...that drain of pilot is always unfiltered, uncooled (so no back pressure there)
I'll give the straw trick a try tomorrow. Thanks. I did check Pilot pressure at the spool and it was 500psi. I've been wondering about the actual pedal valve.
Bill, Search the forum for "cat 312 BL hyd problem " and that will give you my story.
I think I am getting closer to my problem. I did the straw trick. With the line removed and plugged the straw moves when the opposite side activated. However as soon as the line is hooked back up my problem reoccurs. I'm thinking that somewhere the line is not dumping the oil quickly enough and it is locking the spool from moving until enough pressure is built up to force it out then the track moves. Also I looked for a travel alarm but didn't find one. There is a switch on the main valve under the cab and also a fuse for an alarm and also a fuse for the backup alarm. Both fuses are good. Not to sound dumb but where would the alarm be mounted? I looked all over for it but to no avail....
I'm looking at a 6GK schematic as I don't have any grey iron literature. Not much going to stop the oil from returning freely except a kinked hose somewhere. Or, something goofy going on in the travel pilot valve in the cab causing back pressure there. Sometimes the inner wall of a hose can collapse and act like a check valve (flap of rubber) but that is rare. The fitting where pilot SUPPLIES the travel pilot valve does have a screen in it, but the drains fittings don't. However, who's to say the factory didn't install the screened fitting in both spots... taking hoses off the pilot valve under the cab and blowing some air through various ports while you pump the pedals may dislodge a piece of debris.
you change the hose routine at the swivel and the trouble change place. From now I will change the hose routine under the pedal lever and see if the trouble change place. if so, the trouble is in the travel lever spool. you can also change hose routine at the pilot hose main control valve that actuates the travel spool. keep us informed
Bill, reference your travel alarm. Looking at a 6GK-prefix 312 the alarm appears to be under the LH side of the chassis at the front. According to the wiring schematic it's "An attachment" therefore it's possible that not every machine was equipped with them. Again according to the schematic it's located close to the electronic control for the pump and it uses the same branch of the wire harness that contains the pressure switch for the A/C system. Look for a 2-pin connector with a 121-Yellow wire and a 321-Brown.
Pilot hoses swapped left to right. The good news the problem stayed on the right hand track. So it would seem the pilot system is ok. Now the bad news what could be wrong with the main valve or there could be problem in the drive hoses with it coming apart and blocking the flow. I took the travel spool out and saw now issues there at the same time the right spool was also removed.
don't know if you have some pressure gauge, but now the test that should be do is to connect 2 pressure gauge with a ``T`` fitting on both end of that bad workin spool. you will see the pilot pressure going here and if you are loosing some pressure between the spool and main valve (already see that). you will also see if both pressure goes to 0 when you leaves the lever to neutral. play with the lever and read the gauges pressure. The main control valve high pressure can also leak between the main valve and making a hydraulic lock in one of the end cap of pilot pressure. When the spool removed, inspect carefully the inside of main valve to see if there some crack in there. Its important to check for cracks when all the oil is gone through the port, unless you will not be able to saw a crack...
... but before doing all of this I would start changin the 2 hose at the hyd pump. just to see if the trouble still stay at the spool main valve or it follow the hose swap at the pump. keep us informed!
I might remove the straight travel spool out of the DCV and have a look at the check valve that lives inside the center bore of the spool. Just be careful handling these spools. They are fragile. Don't grab them in a vise with a rag or anything like that - only on flats intended for the purpose.... you need to basically try to not touch the shiny part. Here's the check valve: