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

[melli]

I've posted this on another mini-ex site, but maybe the pros hang here... 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? Been mulling over possibilities...maybe the oil I'm using is too thick...maybe going to AW32 might be better, thicker oil is sucking air into system? Guess, I'll have to pull out manual, and gauges...

 

[melli]

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.

 

[Tazza]

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.

I guess air in the oil could cause the slew to not hold like it used to. Foamy oil isn't right, it could be drawing in air somewhere.
A plugged filter can cause the oil to foam up too.

 

[melli]

I guess air in the oil could cause the slew to not hold like it used to. Foamy oil isn't right, it could be drawing in air somewhere.
A plugged filter can cause the oil to foam up too.

Yeah, filters get changed well before hours requested in manual. Although, the glass filter is good for 500hrs...that might be close to it's expiry date. At any rate, getting a complete filter change all around.... It doesn't foam right away...only when things get hot. And it disappears quick enough, when I idle down and let it cool down. Might try AW32, as I'm out of AW46....get some good stuff for winter.