AgcoAllis hydraulic problem

I have a 1993 Agco Allis 6690.  Sometimes when operating the tractor, the power steering will quit and I can't raise the 3-point; however, the front loader will work perfectly.  I can shut off the tractor and come back later and everthing works fine for a while.  At other times I can start it 2 or 3 times and I have no power steering.  Also, while operating it, it will lose the power steering and 3-point.  Help!  What can I try?

Thanks for the information.  I will give it a try tomorrow!

I know it has been 8 years, but what was the solution to this problem? My 6690 started doing this for the past couple of weeks.   Finally today the inside wall of the left side rear tire was covered in oil, and oil was running down behind the fuel tank near the hydraulic filters.   Something finally broke, not sure what though.   But this description is exactly what was happening to us.   (And our 6680 is in the shop.... can’t figure out why I keep running these guys...)

Yes, our 1995 6690, when using the hydraulics, it leaks around the pump.  After a while the power steering stops working.  The sight glass still shows full.  If you turn it off and let it sit, power steering comes back.   Your point on the O rings actually makes sense, I just wish the pump were in a easier place to get too.

What I have found is that the 6690 seems to be sensitive to low hydraulic fluid levels.  I've (I think) solved my problem by making sure the hydraulic sump is full.  I've never had any luck in seeing the fluid in the sight glass, so what I do is to remove the sight glass and fill the sump until the hydraulic fluid runs out of the sight glass hole.  Another thing to check is to make sure the hydraulic lever closest to the seat return to the neutral position -- if left in either detent position the hydraulics will freeze up after awhile.  Similarly if you try to run with the front end loader fully raised.  I think what happens in each of these conditions is that the hydraulic sump is depleted of fluid, the fluid cavitates in the pump, which causes the pump to lose prime and lock up.  So, to summarize, (1) keep the hydraulic sump level to the point the fluid flows out of the hole where the sight glass is located, (2) make sure the hydraulic lever closest to the seat returns to the neutral position, and (3) don't run with hydraulic rams fully extended.

One other thing to check if oil is leaking around the oil filter.  Make sure that when you removed the old oil filter, the sealing gasket from the old filter was not inadvertantly left on the engine.  Then, when installing the new filter, you end up having two gaskets.  I've never done this on a tractor, but did once on a car.