Cat swing brake issue

This is a spin-off question from my thread on a Cat 311B excavator, S/N 8GR00401.
When I swing the machine it operates smoothly but at times I’ll move the lever to start swinging and nothing happens. If I wait 10-30 seconds it will swing like normal. I also noticed that some of the time when it was “stuck” I could move the lever the opposite direction and it would then swing normally in both directions. Curling the bucket also releases the brake and allows it to swing. Switching it in fine swing mode does not to fix this.

Since I had to repack the swing gear cavity I know that the outer swing gear is in good condition all around. Also, when doing that maintenance I swung the house in both directions numerous times without issue. To me, it feels like the swing brake isn’t disengaging. Also, on several occasions the swing brake would apply itself while I was working and actively swinging the machine which caused it to abruptly stop swinging.

It seems like an electric problem since it is intermittent. However, I also believe that the problem became worse as the hydraulic oil heated up? So I’m not sure where to go from here.

Suggestions on how to diagnose or repair this problem? I have a video of the problem but can’t seem to upload it to this site. Thanks in advance!

Good day
Please see attached while it is for a 312 I believe it must be very similar for the 311, no doubt the Cat guys on here will correct me if I am wrong.
kind regards
Uffex

I believe the 311B is a gray market machine with an articulating boom. It will likely have an electrical safety system installed that is supposed to prevent the bucket from hitting the cab. A photo of the machine and monitor panel would confirm what you have.

John- I’ve attached a pic of the monitor panel and overall machine below. Although this particular machine is a gray market excavator it seems that there were some made for the US market as I use that serial number prefix when ordering parts.

You have a standard type machine with the regular house and boom. The only real differences between yours and a North American market machine is the cab. Wiring and hydraulics will all be the same for both.

Swing brake release occurs when pilot pressure switch for both joysticks is closed (pressurized).
If that switch is compromised, it'll do that.
For the life of me. I can't recall where it is.
It closes when any joystick function is activated, but not when travel only is operated.

Is it one of the two pressure switches up on the main control valve bank?



Or is it down with the solenoid on the swing motor assembly?


Hoping the photographs help jar your memory! Lol! What I don’t really understand is if it is an electrical issue why does putting it into fine swing mode not solve the problem? My understanding of fine swing mode was it released the swing brake 100% of the time?

Upon further thinking.

In normal operation, one of those switches closes when travel is active.
The other when the joysticks are active.

But, fine swing puts voltage to the swing brake solenoid regardless of the pilot pressure switch status, as long as the machine is on.

I'm now more inclined to suspect the swing brake solenoid wiring or the solenoid itself.

Forgive my ignorance, is the swing brake solenoid the one circled in my second picture above? The one mounted to the swing assembly?

I was able to run the machine a bit more today trying to see if I could diagnose the problem further. What I did find is that it is definitely heat related. The machine ran smoothly until three bars registered on the hydraulic oil temperature gauge. Shortly after that I could feel the swing brake dragging and it wanted to engage while I was using the machine. Because I didn’t want to damage anything I stopped using it and let it cool, after about 30 minutes I was able to fire it up (2 bars on the hydro oil temp gauge) and again use it smoothly until the cycle repeated itself.

Unless this information points to one sensor or area to check in particular, I’m kind of over my head on this one. I reached out to a local mechanic who is a former cat service tech and he said he should be able to fit me into his schedule within the next week. He’s very familiar with the B series cat excavators and said that he fixed a problem similar to this on one not too long ago.

Good day
You could wire a lamp into the solenoid line as according to the diagram you need the solenoid to be powered up for brake release, that would confirm a signal failure. (Nice photo's the one you illustrate is free swing)
Kind regards
Uffex

Just to circle back and post a conclusion in case someone has a similar issue in the future- mechanic traced the issue to a faulty harness/ground under the cab. I wasn’t there when he fixed the problem so no pics unfortunately. I ran the machine for several hours yesterday and there was no issue with the swing brake. Thanks all for your help with this issue.