Bobcat 331 - Slew not holding, bucket not overpowering thumb, foam in reservoir

[melli]

My Bobby was acting odd today...while holding a log on a slight incline, the machine wanted to slew very slowly downhill while in idle. Normally, it holds position (normally it feels like it locks in position). Also noticed bucket curl couldn't overpower thumb (which it should do)...Lastly, noticed a little bit of foam in sight glass...it was hot, and while letting machine cool down, the foam quickly dissipated.

Bad section in pump? Relief valve?

I keep the oil fresh, albeit I went with a no name big store bucket of 46.

All of these problems might be related to an air leak sound I had a couple of weeks ago through reservoir cap. I cleaned the cap...didn't appear to be the problem (wasn't all dirty).

Air getting in system somehow and causing all these problems?

 

[melli]

My Bobby was acting odd today...while holding a log on a slight incline, the machine wanted to slew very slowly downhill while in idle. Normally, it holds position (normally it feels like it locks in position). Also noticed bucket curl couldn't overpower thumb (which it should do)...Lastly, noticed a little bit of foam in sight glass...it was hot, and while letting machine cool down, the foam quickly dissipated.

Bad section in pump? Relief valve?

I keep the oil fresh, albeit I went with a no name big store bucket of 46.

All of these problems might be related to an air leak sound I had a couple of weeks ago through reservoir cap. I cleaned the cap...didn't appear to be the problem (wasn't all dirty).

Air getting in system somehow and causing all these problems?

Nobody got nothing?
Well, after pouring over schematics, I figured I ought to try looking at build up valve on manifold. A - It is the easiest thing I can pull out and B - it actually might be the problem. It might be dirty/stuck open, and it is connected between pump and swing motor (sits on manifold).
Apparently, it keeps the line charged at 150psi. If stuck open, it would allow fluid to backtrack to pump...and when at idle, the house was creeping downhill. Not sure if it would contribute to foaming in the tank....
Not sure what is happening with thumb (aux) overpowering bucket...could just be a port relief valve not doing it's thing...
Just odd everything happened at once....they must be connected.

Actually made up a test kit to check pressures at ports on manifold, but it appears I have the wrong quick connect...rectify that tomorrow I hope.

 

[pmsmechanic]

Usually air in the hydraulic system means that there is a leak on the suction side of the pump. I recently replaced one of the suction hoses on my mower and I was impressed with how much better the mower performed.

 

[melli]

Usually air in the hydraulic system means that there is a leak on the suction side of the pump. I recently replaced one of the suction hoses on my mower and I was impressed with how much better the mower performed.

Yeah, that would make sense...I'm assuming my suction hose is the monster hose coming from reservoir and plugs in bottom of pump.
It looks ok...no leaks.