Help! Bobcat 337. I changed the boom seals and put it back together, added new fluid to make up what came out of cylinder (about 3 gallons) put it back together. And ran it to get the air out. At first was the usual air in system sounds along with jerky controls then things smoothed out but now the hydraulics only have about 1/4 the power they used to have and very slow. Even the blade goes a little slower and wont lift the machine unless revved up. I ran a bleeder hose from the test port back to the resevoir like the book says to bleed the system and i use a clear hose and do see bubbles/ entrained air. Ive run it for an hour like this and the speed/power just gets slower. Almost seems like the pump isnt shifting off low output or something. . Maybe there is still air in the system thats why im getting no power? Maybe the initial air shocks dislodged or made some valve stick? IDK and looking for input. This machine was running perfect and just came off a job that it ran perfect day in and out until i changed the seals. Thanks
If you have bled system already hopefully before startup. Cycle cylinder over relief maybe that will get trapped air out
There is a procedure for bleeding the system and the system has to be on and i have followed it, maybe for not long enough but at least an hour.. I should note that ALL hydraulics are slow/weak not just the boom.
Odd one. I don't know anything specific about the bobcat, but lets hope it's just got the oil all aerated. Let it sit a day or at least a few hours and try it again, if it doesn't work right away, or within a couple minutes, then shut it off. If it works correctly, but then starts to lose power at some point, shut it off.
Its got a load sense actuated variable displacement pump. It acts kind of like the pump is only putting out the minimum or maybe slightly more. Maybe air got into the load sense circuit and is actuating/ shifting the pump incorrectly or not enough due to air compressing? Or maybe the oil is so full of air that the pump can only put out so much pressure or volume? Ive changed lines before and rebuilt a cylinder on this machine and takes forever to get air noises out of the system but never had things slow down before. Looking back i should have left the boom cylinder rod end unattached to the boom and hooked up the cylinder side line, let it fill with fluid pushing the rod side bubble to atmosphere, then hooking up the rod side line. Would have only created a small air pocket. But as it was i put about 3 gallons of air by volume in the system.
Did you remove/shutoff the bleeder line when testing the machine for functionality ?
Ive tried it both ways. The book says to run it with bleeder line attached and work the machine. Problem is it doesnt have enough power to work the machine. I pulled a sample of oil from resevoir after sitting for a day and full of micro bubbles. But doesnt look foamy
That’s an odd one. Keep us updated, please. Maybe a coincidence not even related to the hydraulic work you did?
I dont like coincidences. In a couple days if things dont clear up or some expert steers me in the right direction im probably going to tear into the load sense relief, load sense bleed and other and some other things to see if maybe the air bubbles dislodged some debris and is hanging a relief open.
More often than it should be, when I’m troubleshooting these situations, contamination is a common culprit. I’ve found rags left behind, dirt & debris jamming something up. I’m sure you work clean. On a few occasions, I’ve seen new hydraulic seals get burnt and melted by hot compressed air when the machine is first operated after a repair. Especially if the cylinder is bottomed out with air still in it.