You didn't say if you were having trouble with steering or the rear lift, but you might use the pressure gauge to see your psi's should be 2250-2500 lbs. We always check the oil levels 1st, I know somebody is going to say duh-huh to that but it's happened before. Next check the Hydraulic Filter these models have wet brakes and sometimes the lining fiber works it's way into the system past the filter,also make certain that the sealing surface is clean when installing the new filter. I think I saw where someone suggested checking the relief valve. We used to work on the 84 series IH tractors I'm pretty sure that the 85's are similar. Hope this is of some help, Tom