I have a 555 that had the same problem. I found a lot of silicone and rust flakes in the transmission that would suck into the inlet screen and clog it. Draining will help, but not fix the problem for me. There is an access plate on the bottom of the transmission. Within that area is a 1/2" pipe plug that is the inlet cross-drilled passage from the screen to the pump. I put together a pipe and fittings that adapt the 1/2" to an air hose and blow air through the passage and backwards out through the suction screen while draining the transmission. I"ve drained the transmission several times using this method and filtered the oil through a shop cloth. I"ve gotten a lot of junk out of the transmission. The best time is just after using the tractor while the junk is still suspended in the oil from all the gear action. I have the adaptor in place with the rear wheels off the ground, then run it for a while through the transmission and spinning it the rear wheels. Then quickly stop, shut off the engine and blow air backwards through that port for a minute or so then remove the drain plug and catch the oil. I have a ball valve in the temporary adaptor so that the air line can already be attached and I just open the ball valve to bubble the air backwards through the screen and into the oil. Be sure to have the fill plug/dip stick removed to allow the air to escape from the transmission cavity or you may blow a seal. Also, within the inspection cover area at the bottom of the transmission is a small tube that has a 1/4" NPT plug in it. It is the pressure test port for the reverser"s oil pump. You can monitor the pump by connecting a hose and gauge to it, place it in a position to observe from the operator"s station, and watch it while operating. It should be a consitent 120 - 160 PSI. If it drops below 50 PSI, you will notice that the reverser clutches begin to slip and indicates that the screen is getting clogged. I used this method to determine what the problem was with my Ford 555 shuttle/reverser. If it works well and then doesn"t, then is is most likely a clogged inlet screen. If I stopped the engine for a few seconds and restarted, the reverser would work excellent until it clogged again in a few minutes. Good luck!
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