Trying to figure out what’s causing this. When I curl the bucket in I can get it to go all the way but as soon as I let go of the joystick the buckle un-curls back about a foot. Also curling the bucket seems slower than normal. Un-curling is completely normal and nice and quick and will hold all the way back no problem it’s only in full curled position that it slightly droops. Anyone have any idea what this is? We had an incident at work where the and boom was fully extended and the operator was on a pivot point on the tracks and ended up causing the excavator to lunge forward and smash the bucket on the ground. We’ve fixed the main bucket cylinder seals and it doesn’t leak anymore but now we have this curling issue.
Have you had someone watch the cylinder rod to actually verify that it's retracting slightly to allow the bucket to move, or is something else going on? Also, are you dealing with mini, or a 400?
Dealing with a 336E
I dont know if that machine got the updated relief/ makeup cartridges or not, but, I'd be curious if a loaded bucket uncurls the same distance. Early relief cartridges would have the makeup spring unwind enough to sit in the relief seat. Replacement cartridges have an additional ring on the master body to show the update. Myself, I'd mark the setting of the relief jamb nut and stem, then disassemble the relief cartridge. If the little makeup side spring tail is stuck in the relief seat, flip the spring over, or, ideally, replace the relief cartridge. A serial number is required to point you to the correct cartridge. The spring getting sucked in occurred on mine when the bucket was slammed into the ground to compact. I've also seen it on the arm (stick) circuit.
Does it continue to slowly uncurl after the initial release, or will it hold there decently?
The spring in question has the arrow pointing to it. The green line is where the updated cartridge has a groove all the way around.
The grooves to identify the updated cartidge is shown in this parts image.
Thanks guys I’ll give all this a shot. We are gonna take the cylinder off our other machine just to make sure it has nothing to do with it and then back track to the area you mentioned
This is that little part sticking out the right side where the cylinder hose tracks back all the way to the valve housing?
To answer shimmy, the bucket doesn’t continue to droop it always stops at that certain point and stays there no problem
We are testing it now, it does super slowly drop back down
Also, when we are digging, when we curl in towards to take a scoop, it causes the cylinder to suck back in so the bucket curls back out instead of holding the curl
Either a bent rod or something is restricting hydraulic flow to the cylinder.
It sounds like the inner piston seal is working as it should, but the cylinder bore is damaged at the very end of travel. When the piston seal gets to the damaged area, hydraulic fluid leaks past the seal and the bucket drops. The damage could be from any condition that interferes with the operation of the piston seal - a crack, pitting in the cylinder bore, or possibly a bulge in the cylinder bore. The incident that you described where the bucket hit the ground hard could have bulged the cylinder bore beyond the elastic limit of the piston seal. Under high pressure, a gap of a few thousandths would be enough to cause the issue.
Changing the cylinder out may be a good idea, if you have another one handy. It could also be a bolt backed or sheared off for the piston inside and causing a dead area at the height of the cylinder opening.