I am having trouble getting the feederhouse to lower on a 4400. It will raise good but it won't lower. Today I removed the control valve from under the cab and put new seals in it but it did'nt help. Yesterday I had a 444 head on it and it lifted fine but when I went to lower it it wouldnt budge. So I opened the throttle a little and it went down but it did a lot of jerking. Today after I put the valve back on it worked up and down smooth 3 or 4 times but when I raised it completely it was like it locked in place and now it wont move at all. I am lost so any help would be appreciated.