How would air enter into a power steering system?

Got a mf205 industrial and I think I'm getting air in my power steering system. Here's what happens:

1. Fill and Bleed - fill the pump while tractor is on, turning wheel back and forth, until practically no air bubbles appear. I do this using a hose attached to a funnel attached to the pump, that way I can see air come up into funnel as I work the wheel. Also, I have the front end off the ground for ease.

2. Test Drive - So I get the system bled, then test drive the tractor for 5-10 minutes turning the wheel back and forth, then as it idles for a couple minutes about a pint of fluid comes out the top of the steering column and I hear a good amount of air escape from within the steering column. So my guess is I'm getting air into the system that builds up to a point where the column seal can't take it.


I've replaced the pump and the column seal, I see no leaks at the cylinders or anywhere else. My steering shaft isn't in the greatest shape, and I don't know the integrity of the valve. If air was coming in the cylinders, wouldn't there be a leak or something indicating so?

After I bleed, the PS works great, can turn back and forth with a finger until I loose the fluid. Fluid is M-1110 equivalent.

Can anyone offer something I should try, should I rebuild my cylinders, or replace the steering shaft eventhough fluid doesn't leak until I get a gas bubble built up, or should I replace the vavle, or the o-ring at the base of the column, or ?

Man Sure hate to be the bearer of bad news but here goes.. You say you replaced the steering shaft seal..Well that seal is not really what holds the fluid down below there in the steering/valve/sector// Your sector/valve is worn and the oil is passing right by the ends of the rotor to the point it has to go somewhere and it comes up the steering tube. Solution, repair or replace the valve and more than likely will be replace.. Mybe someone else will have better news for you but that,s what I am thiking.

Thanks, I've been battling this for a while, I just want to get it working. The nice thing is I can do the work myself which saves on labor...I know the part may be costly, or I may go a route like what Inno did and run some sort of conversion.

Conversion or salvage yard will be the best fix.