M-600 Bobcat, air in hydraulics.

Still fighting the hydraulics on my M-600 Bobcat.
When first started and cool it seems to work fine, after it warms up it starts getting slow and jerky and will finally quit lifting at all ... let it set awhile and it will lift again. I have rebuilt the main valve spools, variable speed valve, variable speed piston, new hydraulic pump .... I'm pretty sure now I'm dealing with air in the system ... I've found when it gets jerky I can raise the lift cylinders to the top a couple of times and it will work again for awhile (pushing air out I assume) Cylinders will slowly drift down also (haven't rebuilt any cylinders .. no outside leaks) Anyone ever dealt with this problem or any thoughts on where the air is entering from ... Thanks in advance for your thoughts and help.
 

Thanks Roger, I have pretty much checked the clamps and hoses the best I can ... This old system has some relief valves inline that I'm thinking might be the problem ... I'll keep trying and post if I ever find the problem.
 

I just went through this with my 444. Mine had been getting progressively worse over 3-4 years. Finally found the problem after replacing all the hoses and the pump.The hyd oil filter gauge there by your right knee? It uses a steel VACUUM line. Get a pin holes from rust and you're sucking air. Get a bigger hole or crack and it does just what you describe.
 
(quoted from post at 05:37:34 10/19/15)
I just went through this with my 444. Mine had been getting progressively worse over 3-4 years. Finally found the problem after replacing all the hoses and the pump.The hyd oil filter gauge there by your right knee? It uses a steel VACUUM line. Get a pin holes from rust and you're sucking air. Get a bigger hole or crack and it does just what you describe.

Mine is long gone but that would be a good place for a leak .... I think my next move will be to replace the clutch pressure relief valve ... it might be getting air through the clutch rods ... I have tried to tighten all clamps and check hoses and will probably start replacing them next ... I appreciate the help ... keep thinking :)
 
I finally found the problem this evening, as some thought earlier it turns out to be the main suction hose at the tank .... yesterday I removed the hose at the tank and cleaned everything good with gas ... replaced the hose and clamped it, then I put red silicone around the end of the hose and let it set for about 24 hours ... ran it this evening moving dirt for a couple of hours without any problems .... I now know where to look if it happens again ... Thanks to all for your help .... WR
 

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