Ford 1520 3-pt lift problem- drops down then jerks back up

[NathanatFork]

I just got this tractor. It is a 1989 Ford 1520 4wd 23hp compact with Front End Loader. 1200 hrs

Shut it down yesterday with the shredder on the 3 pt and it was in the air. Cane out this morning and it was still in the air where I left it. Started it up and after about 30 minutes of shredding and FEL work, I noticed a jerk. Couldnt figure it out at first. Looked back and the shredder would slowly drop a coouple inches down, and then jerk back up. Went it jerks back up, it can felt felt on the whole tractor. Does not matter at what height the 3 pt implement is raised, it still does it. Does not matter if the front loader is in use or on the ground, it still does it. Also, when you use the lever to rais or lower the 3pt it happens in jerks, its not smooth. Then, when you turn the tractor off, it bleeds down.

I checked the hydr fluid and it is full. I do not detect any leaks. Wanted to get some suggestions. Thanks.

 

[firemanpat2910]

Im sure you will get more specific answers soon. But for starters it sounds to me like a bypass valve is stuck, filters plugged, or a valve is stuck open. I dont leave any 3pt attatchment in the air when shutting down. Its not safe and it cant be good for the seals. Possibly if you operate all valves, extend and retract all the way then recheck fluid level, maybe just an air pocket?

 

[Soundguy]

While an implement ont he end of the lift arms is jerking a few inches.. If you look at the lift arms coming out of the lift cover, you will notice them move very little.. perhaps 1/4 to 1/2 inch..

Most likely what you are seeing is the regeneration cycle in the lift circuit after a leakdown has happened. Ford like an unloading style valve system, and what would happen is you move the lift into position, and then it shuts off.. once it leaks down enough to once again trigger the regeneration of the circuit, it 'jerks back up, then shuts off again.

Could be anything from a leaky safety valve, to a leaky piston / hyd cyl oring. If you have an inspection port or a borescope.. or magnet on a stick.. peek in and see if you have oil pouring out the mouth of the lift cyl.. or swirls at the safety valve exhaust.... might be easiest to see by opening the ports and lifting a load, then shutting down and look/listen for the 'hiss' of the escaping pressurized oil at the leak point..

soundguy

I just got this tractor. It is a 1989 Ford 1520 4wd 23hp compact with Front End Loader. 1200 hrs

Shut it down yesterday with the shredder on the 3 pt and it was in the air. Cane out this morning and it was still in the air where I left it. Started it up and after about 30 minutes of shredding and FEL work, I noticed a jerk. Couldnt figure it out at first. Looked back and the shredder would slowly drop a coouple inches down, and then jerk back up. Went it jerks back up, it can felt felt on the whole tractor. Does not matter at what height the 3 pt implement is raised, it still does it. Does not matter if the front loader is in use or on the ground, it still does it. Also, when you use the lever to rais or lower the 3pt it happens in jerks, its not smooth. Then, when you turn the tractor off, it bleeds down.

I checked the hydr fluid and it is full. I do not detect any leaks. Wanted to get some suggestions. Thanks.

 

[JC-jetro]

Ditto on all that Soundguy said. Just difficult to identify without testing each problem area and some such as lift piston seal and open center hyd valve can be expensive and also extensive as far as amount of work to diagnose the problem. As soundguy said I think Safety relif valve can be a culprit. The good thing is it can easily be checked. the pic below shows the lift cylinder head and the relif device. the first check ball check along with the rate of the drop hole provide pressurized oil from the hyd valve to lift the piston. The second ball with the stiff spring is the safety... at times the spring is also has a few shim washer each adding about 50 psi of stiffness to the spring. if you have a shock load.. say lifting your 3 point up in the air with the brush hog at the end of it and you're high tailing in the filed and hit a bump or hole causing a shock load to the lift system then the second ball check will relive some pressure to keep the piston seal from damage or rupture. On my case the little steel ball was out of round a bit and ended up removing the shim to relive the shock load even quicker and also keep the 3 point slowly from dropping due to a very small leak by from the safety ball check.