JD 750 4wd 1983 with 550 hrs has jumpy rear lift

[evolr]

I have recently purchased a fairly nice low hours JD 750 tractor that has a 3 cyl yanmar deisel and runs great. It came with a 261 mower and a scrape blade. All works fine except when I gently try to lift an attachmnet it jumps violently rocking the tractor. This is ever time and even when I am trying to ease it up. I changed the hydraulic fluid with JD fluid and clean the screen well with carb cleaner but did not replace it. Anyone have similar experience or ideas ?
Thanks, Rick

 

[timb]

Ok - real dumb question - does the 750 have a rate control on the 3-point? Might just take a turn of a knob?

 

[evolr]

No, It has a shutoff valve and and a valve that controls the rate of drop but not the force of the lift. The lift works well and holds the implement up all day up it's just when you touch that lever and raise it to lift the attachment it jumps hard and the tractor and the implement rock and forth from it. It's just like it has too much force. I have been told that there is a blockage somewhere but I have no idea where. I can't see replacing a pump that works that well.
Rick

 

[RoyJackson]

There's probably a check valve in the system. I suspect it's sticking and needs to be replaced.

This isn't the first post on a "jerky" 3PH. Last time I read one, it was a 43xx series machine and the check valve was the culprit.

 

[evolr]

What do you mean by "Check valve".? There is a pressure relief valve but it appears ok ? There is nothing in the Hydraulic system labeled as "Check Valve".


Rick

 

[evolr]

I have been reading some of the other posts you referred to where the "check valve" was clogged with a metal particle leading to the problem. I just change the hydro fluid and the previous owner had not changed in a long while and it was dark and had small metal parts in the fluid as well as the screen filter. I wondered what would be an equivalent valve to look at on a 750 and was the check valve referred to acessed from outside or did the whole hydro system have to come apart ?

Thanks, Rick