Hydraulic lift issues (not working)

[bullslayer]

We acquired a Gray Model ZL2201 recently and everything worked great mechanically sound but there was a hydraulic leak which I did not notice because I did not use the tractor often enough. Lift worked fine but the next time I used it to mow with I noticed the lift would not work anymore. I took fill cap off to check fluid level and it was below drive shaft almost to the bottom of drive train case (housing). I added hydraulic fluid not knowing what level to stop but I covered drive shaft. I started tractor and raised arm to apply lift but it still would not work. I went ahead and mowed with tractor but after I stopped lift still would not work. There was a lot of air bubbles in the fluid so is it possible that air is in system and needs to be bled? I hope this is all that is wrong, please help us. I do not have a manual for this tractor, probably need to get one but in the meantime if anyone could help me diagnose this problem and tell me how to bleed the hydraulic system, if that is what is wrong with it. If there is a mechanic that works on this tractor model, please provide me with a phone number where I could talk with him, or suggest someone to take it to if I can not fix it. I live in Kaufman County, Texas.

Thank you,
bullslayer

 

[J_J]

Most hyd systems will usually self bleed as you use the cylinders.

If you have air bubbles in the tank, you probably have a air leak in the suction line.

You may have lost prime.

Have you replaced and cleaned all the filters on the tractors?

 

[bullslayer]

I do not have an owners manual, so I don't know what filters to clean or identify filters you are referring to. I am not a mechanic but if there is something that you can tell me then I will do the best I can to clean filters you are referring to. Can you reply and tell me what to look for?