Boom Cylinder Extends But Will Not Retract

[Howey Matt]

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.

 

[Vetech63]

The hydraulic shop just rebuilt the main control valve and bench-tested it, so I doubt it's the issue.

Its either this, or something was hooked up wrong on the reinstallation.

 

[Nige]

Just so that people know the complete back story. Do your final drives work OK now.?

https://www.heavyequipmentforums.co...one-side-bogging-down-engine-cat-304cr.95940/
https://www.heavyequipmentforums.com/threads/how-to-bleed-air-from-hydraulic-system-cat-304.96563/
https://www.heavyequipmentforums.co...ic-valve-rebuilding-main-control-valve.97095/

 

[Mobiltech]

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.

 

[Howey Matt]

Just so that people know the complete back story. Do your final drives work OK now.?

https://www.heavyequipmentforums.co...one-side-bogging-down-engine-cat-304cr.95940/
https://www.heavyequipmentforums.com/threads/how-to-bleed-air-from-hydraulic-system-cat-304.96563/
https://www.heavyequipmentforums.co...ic-valve-rebuilding-main-control-valve.97095/

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.

 

[Howey Matt]

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.

Is this the same as the load control/check valve mounted on the boom?

 

[Mobiltech]

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.

 

[Howey Matt]

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.

 

[Nige]

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.

 

[uffex]

Good day
Can you hear any clonk when you raise the boom cylinder ?
Kind regards
Uffex

 

[Howey Matt]

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.

 

[Mobiltech]

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.

 

[Tags]

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.

 

[Howey Matt]

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.

 

[Vetech63]

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.

 

[mitch504]

I checked 2 hoses twice yesterday, when I started it up, I still had them crossed.

 

[Howey Matt]

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.

 

[Howey Matt]

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.

 

[Vetech63]

I'm still not sure if you have a pilot system problem with the swing or a main control valve issue.

 

[Howey Matt]

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!