All...i just got a 580b that was given to me. It sat for about 8yrs. Put in a new radiator and drove it home. Moved it to my dig site and it quit moving. Lost all power to the wheels. I changed the transmission fluid and filter. It had some water in it (rather milky). Ran and moved fine for a while then quit again. I changed the fluid and filter again (got some more milky stuff out but looked better. Now I start it and the pressure gauge goes up to the green and you can hear the pump. I can put it in gear and it does the same, but when I shift the shuttle to either forward or reverse the pressure goes down to about 1/3 between nothing and green. Wheels spin but you can about stop the wheel by holding onto it. Take the shuttle to neutral and it goes straight to green again. I'm guessing maybe shuttle control valve (one the "clutch" pedal connects to) is had but I'm new to these things. Any advice would be muchly appreciated.
I am far from an expert but typically friction material is designed for oil only. Any water and they delaminate.
Pretty sure it's a pressure issue. From everything I've been reading the fluid pressure seems to be the most common problem.
First off which oil and filter did you change? Second we need to find out which shuttle you have. There are two different shuttle clutch packs. One is a Rockford and the other is a Twin Disc.
How can you tell which one you have? I purchased a 1973 a couple years back and am still learning.
I read the 580b has a suction screen on the transmission that could get plugged and cause that issue, especially if the fluid was already contaminated