Swing Brake Not Working/Machine Drifting to One Side - CAT 304 CR

[Howey Matt]

Cat 304CR (NAD00987)

Hey guys,

This machine is developing a drift to the left. When I swing to the left and then let go of the joystick, it drifts a little before stopping. It will also slowly rotate downhill to the left on its own. No issues to the right. I read there is a swing brake somewhere. I wanted to run this past yall before I go tearing things apart in case it's something simple.

Thanks!

 

[uffex]

Good day
The issue you have described would relate to the check valve in the head of the motor. If you remove the valve, be sure to check the seat as well as the valve.You can see illustration on page six of the attached.
Kind regards
Uffex

 

[Nige]

This machine is developing a drift to the left. When I swing to the left and then let go of the joystick, it drifts a little before stopping.

If you counter-slew to stop the machine when swinging does it drift just the same.?

 

[Howey Matt]

If you counter-slew to stop the machine when swinging does it drift just the same.?

It comes to a stop faster, but not as abruptly as letting go of the stick when swinging to the right. When I let go of the stick while swinging right, I feel what seems like a brake engage. I don't feel this when I let go of the stick while swinging left. It's more of a cushioned, slow stop.

Also, I noticed the machine takes longer to start swinging to the left than it does to the right. When I push the joystick right, the machine moves almost immediately. Swinging to the left takes a second before it starts to move.

 

[Mobiltech]

Sounds like one cushion relief valve is weak or needs adjusting.

 

[Howey Matt]

Well, I had to pull the motor to get the relief valves out. There's one on each side. No obvious damage. I suppose the seals could be worn out?

 

[Howey Matt]

I found this valve as well. It was very stuck. There's a ring around the inside of the bore about where one of the o-rings sits—probably sitting a long time with water in the oil.

If this valve was stuck, would it cause the issues I was experiencing? I'm not entirely sure what it does. It's the only thing I've found that didn't seem to be working correctly.

 

[heymccall]

 

[uffex]

Good day
Great picts see attched you are in the wrong spot remember to check the seats.
Kind regards
Uffex

 

[Howey Matt]

Good day
Great picts see attched you are in the wrong spot remember to check the seats.
Kind regards
Uffex

Those are the makeup valves. They looked perfectly fine.

 

[Howey Matt]

I put new seals on the relief valves and the other valves I came across. I reinstalled the motor - same issue. I tightened the relief valve adjustment screws all the way in on both relief valves - no change on either side that I could tell. Left still doesn't want to stop quickly.

I can hear what sounds like a relief valve opening (very faintly) as the left swing is coming to a stop. It doesn't sound like it's coming from the swing motor. Is there another relief valve that would come into play here?

 

[uffex]

Good day
How god is the seats to the make up valves?
Kind regards
Uffex

 

[Howey Matt]

Good day
How god is the seats to the make up valves?
Kind regards
Uffex

They looked fine to me. No damage that I could see.

 

[uffex]

Howey I cannot see the mushroom shaped part!

 

[Howey Matt]

I swapped the two relief valves on the swing motor. No change.

I swapped the two supply lines at the swing motor, and the problem switched sides. At this point, I don't think it's the swing motor.

I checked the pilot pressure on the swing control valve. Right around 400 psi each way. The gauge jumps to 400 psi smoothly and quickly.

I checked the supply line pressures at the swing motor. Swing right 3,200 psi. Swing left 2,800 psi.

Watching the gauge, swing right jumps to 1,000 psi, pauses for a split second, then jumps to 3,200 psi. Swing left slowly builds from 0 to 2,800 psi or so over the course of a second or so. I think this is why it takes a second for the machine to start swinging left.

I pulled the valve spool and didn't find any issues. It moves easily through the bore. The springs look fine, although I suppose one could be weak. Is there anything else it could be? I may try swapping the springs next.

 

[heymccall]

 

[Howey Matt]

Another thing that makes me think it's the valve/spoon.

When I released the joystick, the pressure held in the lines for a while. It slowly went back to zero. This was for both directions. The pressure should return to zero immediately when the joystick is released and the spool returns to the center.

I think the spool is getting stuck somehow. It wasn't stuck when I checked it - it seems to move freely. The entire main control valve was rebuilt not too long ago.

 

[Nige]

Yes we remember your issues with the control valve. Has this issue with the swing been there ever since the valve was worked on.? If the answer is yes then amongst other questions how do you know it has the correct springs in that particular section, or if they are correct are that up to spec as regards spring rate.?

 

[Howey Matt]

Yes we remember your issues with the control valve. Has this issue with the swing been there ever since the valve was worked on.? If the answer is yes then amongst other questions how do you know it has the correct springs in that particular section, or if they are correct are that up to spec as regards spring rate.?

It has always been a little weaker swinging to the left, but coming to a stop has never been this bad before.

I don't know if the springs are correct. Is there a way to test them?

 

[heymccall]

I suppose at $75UsD each that I'd wanna know little more.
Do they compress the same?
Do they have the same static height?
Can the spool be reversed?