Having an issue with the stabilizers bleeding down, rather quickly. Rebuilt both cylinders, rebuilt control valve, replaced both spools they were in really bad shape, and just replaced the pilots, all cat parts. They still bleed down, can’t find anything else in the system that could be causing a problem, the only thing I can think of is I cut a piston seal during assembly. But it had this problem in the beginning so what am I missing? Thanks Cat 420D serial BLN 11019
Did you remove and reseal both load check valves in each stabilizer valve?If the load check valve is working correctly, the cylinder won't move if the control lever is activated while the machine is off. There are several Orings per valve section, and one valve is up drift stop, and the other is down drift stop. These stop oil movement of the stabilzer regardless of the quality of the spool or it's bore, as they are between the cylinder and the control.
Is this the spools?
After I got back and was able to get on the computer and look at this, these where both replaced, the only thing reused was the end caps.
Both complete assemblies was replaced new.
Maybe those rebuilt cylinders are leaking.
Yea I’m ordering a new piston seal so I can pull them back apart. Might have cut one during assembly. This was already on my mind, just making sure I didn’t miss anything. The problem is this is what it was doing before I started, and basically replaced everything new. Thanks
There is also the possibility of a crack in the valve body. There is no need to take cylinders apart to check the piston seals. Raise the stabilizer all the way up. With the control valve in the neutral position remove the line on the high side of the piston. Start the tractor and try to raise (push) the stabilizer further. Little to no oil should be coming out of the fitting on the cylinder.
Which valve body Are you referring to?
The entire assembly. The stabilizers and any valves bolted next to it. I am not familiar with backhoe control valve in your 420D. The valves I have worked on all the different valves are stacked together and then held together with long bolts. When Nige reads this thread he will need the tractor serial number.
Fortunately the OP already posted it - BLN11019. Am I right in thinking you want him to first raise the stabilizers all the way up and then disconnect the two hoses connected to the top end of each cylinder at the point marked 23 on the diagram.? Then try to raise each stabilizer in turn and see what in the way of oil comes out.?
Yes, cylinders rebuilt, then valve body rebuilt with 2 new “spools” only thing used was the end caps and bolts, and then today replaced the pilot valve assy on the operators station.
Did you out put the new spools in the old valve body ?
He is wanting to know how to check piston seal leakage. I suggested that he dead head the cylinder, remove the hose closest to the piston and then apply pressure to cylinder. Little to no oil should come out of the open port on the cylinder barrel. Due to the fact both stabilizers are leaking down rather quickly, indicates that he has a valve problem. IMHO.
The left side bleeds down rather quickly the right is slower, like it has a blown seal then the other side is slower catching up. I will go try your test and see what happens in a few days, got other work going on right now. The valve assy has two spools and end caps only, I replaced the spools and cleaned up the end caps And assembled. I will try to find a pic. The speed at which they bleed down seemed to increase after I resealed the cylinders.
There is NO common shared plumbing among the outriggers. They are two independent circuits, unlike the front boom cylinders. And, regardless of spool/ bore condition, the load check valves are between the spools and the cylinder. And, both leak down, BUT, do they leak UP. Raise the rear tires a couple inches off the ground using the stabilizers. Does the "up" drift match the down?
I have not seen these, the lines go from the cylinder straight to control valve spools. I have not checked since I have replaced everything but we have raised and let it sit and they did not bleed off, they held fine In the air. Just bled down when raised to store, I will be back over in a few days and can check this again. I believe the load check valves are built into the spools that I replaced. They are not manual spools, controlled by pilot pressure. Thanks
If the machine stays up in the air when raised by the outriggers, the cylinders are, most likely, good. And, again, the integrity of the spools and their respective bores are NOT a factor in this diagnosis, period. It is the load check valve for the respective circuit. And, again, for clarity, each stabilizer circuit is independent, as independent as the boom circuit is from the bucket circuit.
Thanks I will check into this when I get back over there.
Sir I am unable to find any check valve in the system that Tinkerer is referring to, do you have a part number or is it built into the spools? The hyd. Lines go straight from the cylinder to the spools. Thanks
Sir it appears the check valve you are referring to is built into the spools that I have already replaced with new ones. Thanks
Did you replace the complete valve section for each of the stabilizers.? That would have been pretty expensive I would imagine. I'm referring to the assembly marked #10 in this illustration.
Yes sir I broke it down to clean and reseal and it looked pretty rough so I made the decision to replace with new, and Yes they were very expensive, the only thing I reused were the end caps and tie bolts. I also have a post for a D5B steering issues if you don’t mind looking at that post. Thanks Greatly.