Increasing JD 750 Hydraulic Pressure

[nunyabinis]

I just purchased my very first John Deere. Wooo Hooo!!! A sweet 750 with only 1500 hours and MFWD.

Anyway, it runs the heck out of the 4ft Land Pride bushhog that came with the tractor but it will NOT lift my 6ft disc harrow. I can hook up the disc and pull the hydraulic lift lever up then go to the back of the harrow and apply perhaps 50lbs of upward pressure by hand and the tractor will lift the harrow. I know that the harrow is technically too big for the tractor but it's a high dollar set of harrows with worm screws to easily adjust the pitch of the disks so I figured I could just adjust the harrow to take smaller "bites" when using it with the 750.

Is there a way to adjust the hydraulic pressure on a 750? All she needs is a little more umph.

 

[kennyd]

Welcome to TBN

There IS a way to do it-but you need the proper tools and the factory service manual to find the relief valve.

And a I agree that the 6' harrow is to big...

 

[nunyabinis]

Thanks Kenny.

I ordered the Parts and Service Manuals from JD about a week ago.

I found the exploded parts view on the JD website and it looks like there are some shims that can be added to the relief valve to increase the pressure. It looks like the shims are #19 in the following picture:


http://s245.photobucket.com/albums/gg73/nunyabinis/?action=view&current=JD750Hydraulics.gif

Does this look correct? Does anyone know how thick these shims are? It should be a simple matter to construct my own "shims" to help boost the pressure a tad. Does each shim boost the pressure by approx 100psi?

I've compared the specs on the 750 to a newer 790 and both of them have the pressure set at the factory at 2050 psi. I've read numerous posts regarding a shim kit for the 790. Does anyone know if the 790 kit will fit a 750 as well?


Sorry for all the questions. Although I'm no expert on tractors, I'm pretty handy with a hammer, MIG welder and plasma cutter.

I don't want to lift a mountain...... just that set of harrows.

 

[kennyd]

OK, since you've read the 790 post's, then you know basically how to do it. I am being reserved for as reason...I don't want you or anyone else blowing their machine up!

PLEASE invest a 0-3000PSI gauge setup before playing with the shims. This $30 investment can save hundreds or thousands later!

I am not sure how thick the shims are-but I think a pack is only a couple dollars or so at the dealer so I don't think there is a benefit to making them yourself.

 

[nunyabinis]

I just ordered the shims from JD.


Any recommendations on where to get a 0-3000 psi hydraulic gauge?

 

[kennyd]

I just ordered the shims from JD.


Any recommendations on where to get a 0-3000 psi hydraulic gauge?

I got mine from the SurplusCenter, along with a 1' piece of hose (should have got 2' though) and a NPT F-F adapter. TSC also sells them if you have one close. I got the QD nipple from JD because no one locally had the right ones.

 

[nunyabinis]

Since I have no hydraulically actuated attachments on the JD 750 at this time, I was thinking about permanently replacing plug #26 in the following picture with a 0-3000 psi pressure gauge.


Image of JD 750 Hydraulics - Photobucket - Video and Image Hosting



Is there any reason I shouldn't do this?

 

[kennyd]

Since I have no hydraulically actuated attachments on the JD 750 at this time, I was thinking about permanently replacing plug #26 in the following picture with a 0-3000 psi pressure gauge.


Image of JD 750 Hydraulics - Photobucket - Video and Image Hosting



Is there any reason I shouldn't do this?

I am not sure if that is the "test port" or not...the FSM will tell you when you get it.

 

[dirtworksequip]

Would there be any concerns about vibration ruining the gauge?

 

[kennyd]

Would there be any concerns about vibration ruining the gauge?

As long as it's a fluid (Glycerin) filled gauge it will be fine, plenty of fluid filled gauges are used on heavy equipment.