New (to me)1566 with hydraulic problems

1975 1566 doing weird things with hydraulics. Sometimes the work well with engine about 1000 rpm or above. Then after about 5 mins of runtime, the steering quits altogether (not even manually. The wheel won't even turn. ) front blade won't raise or lower, three point acts funny, and ta quits working. If I shut it down and wait 5 mins, it will work but the cycle repeats itself. When it works, blade will lift tractor off the ground and will not leak down. Ta works fine when the issue is not happening. So does the three point. Hyd fluid is very milky, but full. Thanks. A.P.

Upon fiddling with it a little more, I raised the blade, shut off engine, then lowered blade slowly. When blade was going down, I could hear fluid rushing through the lines with slot of air in them. Then I could hear air pressure bleeding through trans dip stick. Then I pulled dipstick and air blew out under pressure. Where is this air coming from......?
 
First place to check for air leak is filter cover. Lot of those covers don't fit great and also, some 0-rings get cut putting cover on. Have you changed filter because with a milky oil it may have softened up the filter making it even more difficult to draw oil through it so it goes through the bypass screen on end of filter, plugs that , which doesn't take that much. Aerated oil will turn milky looking also even if no moisture in oil. Not likely though. After checking cover, you can add extra oil to cover possible internal air leaks but may not want to waste new oil if it needs a change which it sounds like it must. Three most likely places to suck air, the cover on filter, 0-ring between front and rear sections of transmission and the o-ring on main suction tube in top of filter cavity.
 
Pete is correct. Replace the oil, then Over fill by 5 gallons (not a misprint). If that does not fix it, let us know to get the next procedure. Jim
 
Someone will chime in, or it will be in the book. I will guess about 15 gallons. Overfilling is the part of my post above that is the solution. Just filling will not make it better. There are components in the pump intake system that have a habit of failing "O"rings. 5 gallons covers the "O"ring so it can only draw Hytran. Jim
 

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