520 Power Steering Issues

[PushnFords]

I'm working on a 520 and the power steering isn't quite right. I've gone through the system 100% so everything has been rebuilt. The worm gear is a late serial number version. When the tractor is first started it'll sometimes spin the wheels to full lock left OR right without touching the steering wheel. Also at idle on smooth concrete if you flip the steering wheel one direction or another it'll continue to turn to full lock by itself...and it'll do that going either direction. When driving it sometimes wants to follow the curve of the road...if the road is sloped it'll try to steer itself down hill. I don't think it is a problem with the centering valve adjustment because the problem is the same whether steering right or left. I backed the control valve adjustment stud all the way out but it still does it. There is a stack of washers inside the control valve that the book says adjusts steering effort so I'm wondering if I need to adjust though to make it steer harder? Are there other things I should check? When I took it apart none of the surfaces were in great shape but I polished everything up as good as I could and honed the control valve passages so the valves would slide smoothly. I'm using the JD P/S oil in it.

 

[ET]

Is the bolt that holds the fork on the spool valve tight?

 

[JDJACK]

I am working on a 520 power steering also. If you honed out the valve housing then there might be fluid leaking by valve.
Rich Duane might chime in here, he knows these systems very well, and reproduces parts for the power steering systems. That spring allows the steering wheel to came back to center, if I understand it correctly.

 

[ET]

Here is another thought. When you installed the adjusting bushing in the worm gear, did you pull the center shaft forward so the threads on the inside of the bushing caught slightly before the threads on the outside of the bushing? Honing a spool valve housing is not a good thing.

 

[PushnFords]

I disassembled the worm gear, cleaned everything, and then read in the manual that I was supposed to have taken a measurement before disassembly to then use to reassemble the worm gear assembly. I don't remember exactly how I did it but I tried to follow the tech manual as closely as possible. What does the depth of that center part affect?

Yes I know the tolerances in the control valve are critical but when I disassembled it I had to hammer the valves out (carefully with a brass drift) and after cleaning they still wouldn't move back and forth in the housing. I ran a little emery cloth through the smallest hole & lightly hit the others with an automotive wheel cylinder hone. I tried to just do it enough that the valve didn't bind.

 

[PushnFords]

Yes that is tight.

 

[PushnFords]

Yes I may kick myself for honing the valve housing. But the valve was scored & stuck in the bore...wouldn't slide freely even after a good cleaning. I think I talked to Rich at one point about buying a reproduction early serial number worm gear and some reproduction ventilator fan to p/s pump shafts. The tractor's owner opted for used parts which caused a little headache as well. The only worm gear I could find was the later style & the two pins were broken off and took 2-3 hours to extract. I was thinking the spring allowed a little give at full lock so it wouldn't put as much pressure on the pins in the pedestal...one was broken when I disassembled it.

 

[ET]

The bushing adjustment is the return to neutral for the steering wheel and hydraulic valve. It wants to be as tight as possible and still have the wheel spring back to neutral from both directions. The adjustment can be done using a deep socket with vice-grips locked on the outside and an allen wrench put through the center to unlock the bushing.

 

[PushnFords]

Ok so the fact that it goes to full lock by itself or with a flip of the wheel is a pretty good indication that is wrong then? That might be a large part of my problems with this....

 

[buickanddeere]

As previously stated . It's probably loss of control of the spool valve due to wide clearances when the bore was smoothed out. The spool is going full travel without control or feed back . As shown by the wheels going to full lock even through the steering wheel was only turned a little .