I am new, so please bear with me. My 644 hydraulics lock up when it gets hot. After it cools down, they work fine. It has new hyd. oil and a new hyd filter. any help would be greatly appreciated. Thanks, cec271
Lock up is rather vague, do you mean all hyd functions stop working including steering and brakes? But machine will still drive with good power? Any strange noises at the point it stops working? Also, there were many variations of the 644, including the B and E series variations. I don't have tons of experience with Lull machines, but this isn't enough info to take even a wild guess.