Cat 304CR (NAD00987) I've got a boom cylinder that will extend but will not retract. In other words, boom goes up but won't come down. When I try to boom down, I hear noise from the relief valve, but the cylinder only moves about 1/4". I don't have a way to test flow, but I have adequate pressure at the cylinder (~3,800 psi). There's also pressure at the other end of the cylinder, I assume, from the fluid trying to escape. I swapped the lines at the cylinder. Now the machine will boom down but struggles to boom up. The boom does raise very slowly with the hoses swapped, but the relief valve is engaged the entire time. The hydraulic shop just rebuilt the main control valve and bench-tested it, so I doubt it's the issue. Could this be a malfunctioning relief valve? Any ideas would be greatly appreciated.
Its either this, or something was hooked up wrong on the reinstallation.
Just so that people know the complete back story. Do your final drives work OK now.? HeavyEquipmentForums HeavyEquipmentForums HeavyEquipmentForums
Without looking up that exact system I would be looking at a boom drift reduction valve that is either stuck or has no pilot signal to it.
Yes, the final drives are working, even the two-speed. The only issues I'm having now are the boom cylinder not retracting and the machine will not swing to the left.
Is this the same as the load control/check valve mounted on the boom?
I would have to look at the schematic for that machine to be sure but a load check on the boom could do the same thing.
What I thought was a check valve on the boom is just a tee with a valve that allows you to release pressure in the boom and lower it manually. The parts manual and service manual appear to show a check valve mounted on the boom cylinder, with a pilot line run to it, but my machine doesn't have any of that.
I think you may be looking at the 222-1272 Boom Check Valve Group which is an attachment (option). Your machine was not originally built with that option.
Good day Can you hear any clonk when you raise the boom cylinder ? Kind regards Uffex
No unusual noises. It raises perfectly. But as soon as I boom down, I get the relief valve, and nothing happens. With the hoses swapped at the cylinder, the cylinder retracts as normal. It also extends, but very slowly, and with the audible relief valve.
There is a boom drift reduction valve in the main control valve for the boom. Number 13 on this picture. I would check if it’s free or has a blockage on the drain side.
He also stated it won’t swing left. Sounds to me like you’ve got some hoses crossed up when you reinstalled the control valve.
I doubt it. They were all marked and labeled, and I double-checked the boom and swing connections. Something is screwy with this boom drift reduction valve, though. It had pink gunk and flakes of rust inside, and I'm pretty sure mine was missing parts, according to that diagram. I'm going to take it back apart today and have another look. I cleaned it and reinstalled it last night, but it still didn't work.
There was a guy here recently that had double checked his hoses.....and there was only 3 of them. He was convinced he was right and guess what.................he had them crossed. Not saying that is your issue but it does happen quite frequently.
I checked 2 hoses twice yesterday, when I started it up, I still had them crossed.
I removed the boom drift reduction valve again and inspected it. I think it was installed incorrectly. I now have it installed so that it springs up and down instead of being stuck. It looks correct to me, but the service manual and parts manual do not provide enough detail to be 100% sure. I reinstalled it, but the machine still won't boom down. I decided to move on to the swing issue since I wasn't getting anywhere with the boom. The swing valve gets adequate pilot pressure when the joystick is moved left, but there is no pressure at the swing motor. I'm starting to think the hydraulic shop sprayed the main control valve with yellow paint and called it a day instead of actually rebuilding it. I guess I'll drain the fluid again and pull the swing spool to see if there's anything obviously wrong. The service manual says the swing pump assists with boom up functions, so maybe the issue lies with the swing spool.
I switched the swing spool the other way, and nothing changed. The valve is getting pilot pressure (tested with a gauge, and I can see the hose jumping), but the valve is not opening and sending pressure to the swing motor.
I'm still not sure if you have a pilot system problem with the swing or a main control valve issue.
I think it's the main control valve. I just don't know enough about the inner workings to fix it. I suspect it's something simple like a spool being installed incorrectly. Unfortunately, the service manual and parts manual do not provide enough details to confirm. I was hoping the hydraulic shop would be able to figure it out, but it seems like they just cleaned everything and reinstalled it the same way. I suppose I'll keep switching spools around. Maybe I'll get lucky. I really don't want to lift the cab and pull the control valve again. I've done that 3-4 times this summer, and it's getting old!
Don't do this. You're going to create even more problems than you have now. The spools are machined to fit their proper bores only. Also, alot of spools will have different relief and lube cuts for specific functions to work properly.
I'm not talking about moving them to different valves. A lot of them are directional, and they only work if they're installed the correct way. If one of them is installed backward, it could cause issues.
I did some more testing, and I still think the issue lies within the main control valve. The valve controlling the swing left/right gets 400psi of pilot pressure in either direction when the joystick is pulled, but it only sends pressure to the swing motor when it is pulled to the right. The valve gets pilot pressure when the joystick is pulled left, but the swing motor doesn't get pressure. No relief valve either. I'm not sure if the spool is not opening to the left or is opening but not sending pressure to the swing motor. The spool slides in and out of the valve body by hand. I can push on the spool and compress the spring with some force. Everything appears to be operating correctly. I installed the spool in both directions, and the result was the same. I also confirmed that all of the hoses were installed correctly. I followed them by hand. Any ideas??? I'm still having the issue with the boom as well. The boom cylinder will not retract. I can hear a relief valve. The boom cylinder is getting 3,800psi at the rod end. The pressure also builds to 3,800 psi at the base of the cylinder because the escaping fluid has nowhere to go. I cleaned out the drift reduction valve in the Boom I valve and found it was installed incorrectly. I believe it is correct now. I tested it with compressed air, and the mechanism seems to work correctly. Pressure on one of the pilot lines opens the valve and allows pressure to escape. Remove the pressure, and the spring pushes the valve closed. I also followed the hoses by hand and confirmed they were installed correctly. I tested the pilot pressures at the Boom I valve, and it's getting the correct pressure in the correct places when the joystick is moved. I also installed the spool in both directions, and the result was the same. Any ideas? I'm about out. I find it strange that the swing valve is not working. It's a relatively simple valve. Not complicated with check valves or drift valves like the boom. The only thing that could be installed incorrectly is the spool, and I've tried it both ways. The only thing I can think of is that maybe one of the neighboring spools is installed incorrectly and routing fluid the wrong way. I reversed the blade spool because it's right next to the swing valve, but it caused the blade not to work correctly. Any ideas or suggestions on what to check or test would be greatly appreciated!
Good day Checking out the main valve for the slew is straight foward plug each main line with a guage and measure the pressure, your 400 psi pilot pressure seems somewhat low to me, suggest you get the Cat chaps to check that is correct. Kind regards Uffex
Good day The attached may help. Kind regards Uffex
The service manual says the pilot relief valve should be set at 495 +/- 30 psi, so I suppose my 400 psi readings could be a little low, although I think it's more likely that my cheap Amazon gauges are to blame.
400 psi is enough to get it swinging and you have the same pressure both ways but it swings right so I wouldn’t dwell on that. One other thing to check is that the pilot pressure on one end of the spool should be zero when 400 is applied to the other side. If the opposite side is not returning to tank as it should you will have pressure on both sides and the spool won’t move. You could try removing the opposite pilot line. Cap the line and leave the spool end open so it can bleed off. Did you try swapping the swing relief/ cushion valves ?
Were the boom and swing problems present before the valve was removed for reseal? I'm still going back to an installation issue, or the shop didn't get something right. Is this a professional shop that did this?.........Or a "shop" that some guy opened up in his garage?
Good day If you follow the information, you will catch an important point. A fixed displacement system (Servo) must maintain the pressure at low revolutions, as you are starting with a low value. A loss of pressure is indicative of internal leakage, preventing valves fully shifting. If you get the basics as they should be, it's safe to move on. Kind regards Uffex
@Mobiltech , You were right from the beginning! I removed the drift reduction valve, and the boom cylinder retracted normally. I'm 99% sure it's installed correctly -- same as the attached photos. I don't see any damage. Should I see about replacing it? Could be a weak spring. Maybe I can polish the bore where it sits to allow it to move more freely.
This is a great suggestion that didn't occur to me. However, I tried it today in each direction, and I'm still not getting the valve to open left even with the pilot connection on the opposite side uncapped. I confirmed again that I'm getting adequate pilot pressure in both directions. Do you happen to know how far the spool is supposed to move in each direction? When I push on the end of the spool by hand, it pushes in about 1/2" before it hits a hard stop, then the spring pushes it back to the center.
GOT IT!! The tiny hole in this pilot fitting was plugged. It’s the fitting for the left swing. I cleaned it before with compressed air, but I guess it was still partially blocked. I used a thin piece of wire to clean it out this time. The machine is working perfectly now! I’m going to polish the drift reduction valve and reinstall it. I’m not sure if the spring is weak or if the valve and bore are dirty. Either way, the hydraulic shop should have caught it. I expected better from the shop where the Cat dealer sends their stuff. Thanks everyone!
That’s great that you got it. Sometimes you have to dig a little deeper when things don’t add up. Paint on these valves can be a problem when rebuilding but if everything is cleaned properly that shouldn’t happen. I would bet you have an orifice plugged in the drift reduction circuit also. In the schematic pictured it shows an orifice on the drain side of the spool that controls the drift reduction valve. It is just above number 14 circled in pic. See if you can find that in the block.
I couldn’t find a plugged orifice, BUT I got it working. The trick is you have you install one of the pieces of the valve the opposite way the service manual shows. I circled the piece in the photo. Hopefully it saves someone else the headache.
I struggled with a Yanmar excavator for quite a while, swap hoses, test pilot pressure, pilot flow. finally removed the offending valve section the spool itself had a couple nicks on it and would move one way freely but not the other. A chip of cast iron from a thread had gotten into the valve section. I polished the spool on an arkansas stone that was super flat, using oil and a microscope to remove all the imperfections and operation was fully restored. The spool valve with the pilot overlay is almost identical to the spool valve with mechanical control, remove the pilot drives and the spool should come out.