John Deere 40 3 point lift arms

When I start the tractor the lift arms raise about 75 percent of the way up but will not drop down. they will go fully up will I pull the lever up but will not lower past this position until I shut the tractor off. any ideas where to start ?

You don't say if it is a single or dual Touch-O-matic (TOM) system which is the first and biggest question to be answered.

A single has only one control lever to your right with the left rockshaft arm being a single piece.

A dual TOM has two control levers to your right and the left rockshaft arm is actually two arms that can be pinned together or left to operate separately. Most are usually pinned together.

I'm betting you have a dual with the left arms pinned together. I suspect you may have the mode selector and controls set wrong. There is under the seat a lever that either pushes on two valve pins or lets them "pop out" as you flip it from one extreme to the other. Sticks in my mind they're called crossover valves & they're to be OUT for dual operation but don't take my word for it! I don't have the book handy or I'd look. I know it cautions of damage to the system if used incorrectly! I'd have to find and open the operator's manual to advise for sure but it sticks in my mind if the two left lift arms are pinned together (dual mode) you are supposed to flip the selector one specific way. The pins released so they can "pop out" seems right but read that book! Next I believe the shorter of the two control levers to the right of the seat is to be pulled all the way back to the stop and left there all the time. The system will then work fully up and down with position control at any point using ONLY the longer lever! Ours has been set to the dual mode for so many years it's just always set that way. The one selector lever is wired "home" so it can't be messed with!

Check if it's dual or single. My guess is it's a dual. Then set the levers & the mode selector & see if that doesn't make it straighten out. A dual will do what you say if the crossover valves are set wrong & you're controlling with only one cylinder. The damage it speaks of can come from dropping a load onto the 2/3rds raised and closed "other" cylinder like a big hammer.

If that is not the problem, there is a series of linkages and springs in there which follow a cam on each shaft "feeling" shaft position. They push or pull valve rods to cause it to rise or fall. Lowering is accomplished by a wasting operation where a check valve is "bumped" out of its seat allowing oil to escape from each lift cylinder letting it fall. Since you say it raises & lowers part way, it is either the things mentioned above or a linkage/spring problem. Check that simple stuff above first!

When it comes to working on those (deep inside), the IT book does a good job of reminding you on what to do & how if you've seen & used Deere's book in the past. Without having ever seen the Deere book, the IT can leave you scratchin yer head a bit!

Hope that helps.

It is the dual system and I know the lever your talking about. I will check it out and look in the book to refresh my memory which direction it should be, Thanks. I hope it's that simple !