Hi Guys, I have a Komatsu D6 p12 and its not lifting blade when at low revs. Machine has to be at full revs for blade to go up, has anyone got any ideas? Would be much appreciated.
Would look at the hydraulic pump first, seems to me that is where your problem is!
Hi Horst, Thanks for your reply, Pump seems to be working fine as it drives and steers ok, it seems to be just on control of the blade lift.
Have the pump suction filters and screen been cleaned out. Always a good place to start. If lots of debris inside, take a picture and post. Are the lift cylinders by-passing by any chance. They one by-passing will usually get hotter. It is something that will have to be ruled out. Simon C
You have got two separate pumps in the machine, one for the hydraulics and one for the transmission.
Most likely both pumps use one common sump as they do on larger units. Could be sucking air or filter partially obstructed. Needs to be checked before throwing money at it. Check the connections for leaks or worn out o-rings. Simon C
Hi Simon, I don’t think lift cylinders are bypassing as it does lift up evenly no lag in either side by looking at it. Haven’t checked inside the tank as yet, but we will have a look and post pics of anything. It just seems weird that the blade tilt functions works fine as in tilts forward and back, it tracks forward reverse & steers fine. But blade will only lift a full revs. Do you guys know if the pressure compensator valve for the lift spool would create this condition?
It could be a problem in the control valve spool such as a piece of rubber from inside a hose or who knows what. Only a leak test on the 2 lift cylinder would tell the true story. The 2 hoses that feed the ports of the cylinder for going up come from a tee. If the line that feeds the tee is disconnected and dead ended with a gauge you will find out if the pressure is there or not. This test would not cost a lot to do. May have to make up a blank with threads. I would do that before I tore apart the spool, which ever is easier. Simon C
If pressure is too low, Pump or pump plumbing is suspect. Fix and make sure of easy stuff first before buying dollar items. Simon C
It does not require much pressure to tilt forward and back as compared to lifting heavy blade. Dead end the tilt cylinder with a gauge installed on the hose feeding it. You will get a good idea from that what kind of pressure pump is putting out at idle and revved. Maybe problem is in control valve, would perform a few test before ripping all that out. Simon C
Hi Simon, Thanks for your input really appreciate it, I forgot to mention when blade is lifted it creeps down slowly, which I think is headed more towards some obstruction with the control valve spool like you said. We will have a look at a few things you guys have put forward and keep you posted.
It is also possible that the bottom end of lift cylinder packing is leaking , hence no oil leaking out. You will need to do some tests as I said before the money trail starts. Often one lift cylinder will be leaking some making the other one do more work. Eventually the one doing the most work will start by-passing also. At that point it will have to be revved to lift. But if control valve spool is faulty then the cylinder will not lift without RPM and can leak down. You could try a mid stroke leak test to see if the cylinder is by-passing and sending oil continuously out the return port. Be careful when loosening a fitting on hoses or cylinder in case there is lots of pressure so you dont get hurt. Simon C