John Deer 790 jumping

[Rwatson0122]

Somehow water has gotten into my hydraulic fluid causing my tractor to jump when trying to steer or using the bucket. I drained all the fluid out and put new fluid in and changed the filters three times. It seems to work good for a short time but then does the jumping again and won't steer are my pumps bad?

 

[Mike1955]

Somehow water has gotten into my hydraulic fluid causing my tractor to jump when trying to steer or using the bucket. I drained all the fluid out and put new fluid in and changed the filters three times. It seems to work good for a short time but then does the jumping again and won't steer are my pumps bad?

Sir I've been watching this post. I don't have a clue how or where to diagnose this. The water I think is heavier than the oil. So if you quarantine the water and get it out you might be on track. Maybe someone else will chime in soon. Gook luck

 

[loggin]

Somehow water has gotten into my hydraulic fluid causing my tractor to jump when trying to steer or using the bucket. I drained all the fluid out and put new fluid in and changed the filters three times. It seems to work good for a short time but then does the jumping again and won't steer are my pumps bad?

We will definitely need more information. Not sure by what you mean "jumping"? Do you mean intermittent hydraulic pressure?
How many hours on the machine?
Is it a geared or hydrostatic transmission?
Have the hydraulic fluid and filters been regularly changed?
When you drained the hydraulic fluid were there any metal shavings or chunks in the fluid or the filter?
Is the 3 point hitch operating properly?

 

[crashz]

A JD 790 is a collar shift geared transmission tractor.

OP - did you clean the pick-up screen too? Maybe the screen is clogged and starving the pump.

 

[CH4Ohio]

Nothing jumps like a deere . . .

 

[Rwatson0122]

By jumping I mean it will stop and go like when you try to lift the bucket it will stop then go like stuttering so guess it would be intermittent hydraulic pressure. It has 959 hours on its a geared transmission I didn't see any shavings but the fluid when drained was milky white and the filters were clogged. I cleaned the filters and drained it put new fluid in and works for a few minutes then starts messing up again. I think water ran down into the transmission because of a bad gear shift boot.

 

[crashz]

That's a pretty common issue and entry point for water. I never had an issue with my 770 (an older version of the 790) but do know there is a pick-up screen near the bottom of the rear axle that can get clogged. I honestly can't remember where but I believe it unscrewed from the side of the case. Very common to get plugged up. When you say filters, I assume you changed the spin on filter below the floor board, but did you clean that internal screen too?

 

[Rwatson0122]

Yes the pickup screen has some gunk on it cleaned it off still didn't help tractor was running fine before the water got in it.

 

[loggin]

Yes the pickup screen has some gunk on it cleaned it off still didn't help tractor was running fine before the water got in it.

After changing the hydraulic fluid and filters + screen the last time did the fluid come out nice and clean?

How is the 3 point hitch hydraulics acting?

Next step would be to check hydraulic pressure, if the fluid is clean, to see if the pump is functioning properly.

 

[oldnslo]

Does it jump change while engine is idling vs half throttle vs full throttle?

I looked at JD parts breakdown and I believe that model has two separate pumps one for steering and for loader. If this is true then both systems jumping would point towards air leak in pump inlet line or some restriction in the inlet line. That should be the only common element between both circuits.