I have a Cat 312BL series 8JR...When I move in the forward direction, the right track barely moves when I try to turn to the left. This appears to get worse after the hydraulic oil heats up. The left track works fine. Any help in diagnosing and correcting the problem would be most appreciated. Thanks.
Forgot to add the serial#. 8JR00944
Good day The attached may help. H2 Weak crawlers P1.pdf drive.google.com Kind regards Uffex
Questions: 1) Does the same problem occur on the same track but in reverse? (each drive motor has a forward & reverse crossover relief valve) 2) Are any other functions going slow on this machine? Before delving into pressure testing I'd be tempted to pop the case drain lines off both drive motors and compare flow out of each, with oil at operating temp.
Uffex. Thanks so much for the article. Some very useful facts and illustrations. Chrisso. Thank for the case line suggestions. I can certainly give that a try. All other functions appear to work normally. The track works in reverse under all conditions. When I start out running the machine, the problem track/turning works normally. However, as soon as the hydraulic oil heats up past the mid point on the monitor gauge, the problem start to kick in. The higher the oil temp the worse the problem gets. Because of the age of the machine, although only 4400 hours, I am wondering whether this is not related to some bad seals on the central swivel/rotary assembly.
In that case the first thing I would do is swap the forward & reverse solenoids on the track that's faulting... and if the problem changes to the opposite direction you've found the problem. Both relief valves are set to 53** psi, which is above the standard main relief setting of 5000 psi, so I wouldn't bother playing with the adjustment unless you have a set of gauges w/ the cat quick couplers and the proper procedure, etc... which you're going to need if this is indeed the problem, but first things first.
Chrisso. Thank you for the great photo. I don't have any experience in working in that area. What is the procedure for removing/reversing the relief valves. ? do the openings have to be blocked or hydraulic pressure relieved.
Releasing hydraulic pressure is a standard procedure that should be done before cracking any hyd line or removing any hyd component, unless you know the system really well. Run engine for 2 mins to charge pilot accumulator. Shut off. Key back on but don't start. Release park brake (in an excavators case release hydraulic lock). Move/cycle all controls, pedals, auxiliary thumbwheels multiple times or until the machine is fully "relaxed" and stops moving. Loosen hyd tank cap. Hyd system pressure is now released. Nothing special about these valves I can see. Just swap them about. Try not to alter the valve adjustment by undoing the locknuts.
Sorry for the simple question, but I am still confused about the location of the valves. Thanks for being so patient.
Chrisso. Please disregard the previous email. I have identified the area of concern and will complete your recommendations and report back to you.
Chrisso. I stand corrected. I had a job to do at the farm today and tested the track issue again carefully . As soon as I started to use the machine, all track movements were fine. Again, as soon as the unit heated up then the right track was feeble in both the forward and reverse directions. If the machine got a little hotter, then I also noticed some decreased motion on the left side; forward and rear. If I left the machine sit for 2 minutes, all the functioned worked normally for a short period of time but then returned to the above mentioned issue. I am confused (been there before;old age) and would appreciated your further thoughts and diagnostics. Thank you.
That's fine **. In that case refer back to my first post about cracking the case drain lines to both drive motors. That's about the easiest test you can do... but it's messy. High RPM, jam implements nicely into the ground and try to track. Should have a steady trickle of oil from both drive motors. More importantly, compare the pair. If it shoots out of the suspect drive motor, that drive motor is a shot duck. Another thing, pay attention to other implements and machine functions while trying to track. If anything moves uncommanded that's an indication of a leaking swivel valve. Failing all that, you really need the Testing & Adjusting procedures. Start from the beginning, make sure you have the correct pilot pressure to the tracking spools in the main control valve. Also make sure you don't have pressure to opposing side of the spool (indication of joystick/pilot valve failure). Hopefully someone can post them. And if anyone can make sense of this machine's hydraulic schematic, please do share.
Correction: It's really only the blade and tracks you're looking for uncommanded movement in. Think of all the circuits that have to run through the swivel. Lift machine up with the blade & bucket. Command one track function at a time. If machine drops (via the blade) when commanding a track function, swivel is bad. Back on the ground, if a track function nudges when you move the blade, swivel is bad. You get the drift.