Bobcat 435 shudders when slewing down hill

[JakeKraft]

Well, I have another issue with the mini. I was digging ditch over the weekend, and had it on some pretty steep slopes. With a bucket full of muck, and slewing so the bucket is swinging down hill, it will get a real bad, very fast shudder. Almost like the hydraulics are cycling super fast or a check valve is bouncing or something... Its bad enough I have to stop the machine and start slewing from a stop, it shakes the cab and feels like it would break something if I work through it. If I slew full speed it doesnt do it, neither does it do it slewing very slowly. I have no turn-table play, and no noticeable slew motor/gear play. Working on the flat, and slewing uphill, no issues. Just when there is a heavy bucket swinging downhill. Anybody have any thoughts? I dont seem to be getting notifications, but Ill do my best to keep an eye on this and follow up.

Thanks all, Jake

 

[Sagamore1]

I am not familiar with the bobcats but have a couple of first thoughts. Doe it have the problem swinging in both directions or only one? Does it do it when the machine is level? Can you get the machine level on the blade with the same load and see if it does it? I am assuming the angle you are working at is within the machine specs and the hydraulics are topped up. Extreme angles can do funny things to hydraulic flows especially inside the reservoir. The direction you are swinging may just be enough to momentarily reduce flow to the pump. I have struck this before on my old Yanmar. the level looked fine but wasn't due to the angle i was working at. The low pressure may be enough to cause a hydraulic pulse and activate the swing brake, when you slow down the flow returns to normal.Check the swing motor mounting bolts. A (small) bit of play there wont matter on the flat but on an angle it may be misaligning with the slewring. Is there any unusual noise when the shuddering starts? Does it stop slewing as normal?s is the slew brake is activating normally. I am yet to see a Lew gear and ring that doesn't have some wear in it on a well used machine I would suggest turning the machine 180 degrees and see if it still does it. A couple of thou wear can be just enough in particular circumstances to give metal to metal contact. I am assuming everything has a bucket load of grease on it but if it was me i would check everything was tight that i could get a spanner on when the machine was flat with no load and then add at least a half a tube to the slewring through the zerks, slewing the machine 1/4 turn or so every 6 pumps or so and then do it again in the opposite direction. It doesn't take much for a blocked outlet in the grease system to cause a small dry spot which may be just in the wrong spot for the angle you are working on. The problem sounds like something minor you have probably had for a while but didn't notice in normal conditions so start with the basics and eliminate them as the cause
Good luck. I will be interested to know what the cause is when you get it sorted

 

[JakeKraft]

Thanks for the detailed reply Sagamore! The hydraulics are topped up, and the machine is well greased. The loose motor could explain it, ill pull a floorboard and check that tomorrow. It seems like it's happening because the weight of the bucket is pulling the machine downhill, on certain slopes it'll happen only when loaded. It does occur in both directions, and at all speeds, but can be lessened by going slow, and mostly cruised through at full slew. It's almost like the load is pulling the machine faster than I'm turning it, and the brake or a valve try's to stop it slewing until the motor catches up and causes it to open. This happens repeatedly and quickly like "bam bam bam" several times a second until I stop or slow down.

 

[uffex]

Good day Jake
There is a large document regarding slew swing issues you can read or download go Excatech.org >Library>common issues it is free and safe.
Kind regards
Uffex