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Discussion Starter #1
Hi All,
I've been a reader for a while, but just registered now to ask this question. I have a '88 JD750 with P/S and a FEL. I just finally got a
model 7 backhoe after finding a good one at a reasonable price after maybe 5 years (yes, more patience than money!)
anyhow I want to add rear hydraulic connections for the backhoe hoses. - I've read a bunch of threads and I think I almost have it after reading this one
https://www.greentractortalk.com/forums/hydraulics/164449-do-i-understand-power-beyond.html

My question is, using the below diagram from the 750 manual, is it correct to just disconnect the line marked U (PB line at the bottom of the loader valve) from the rockshaft housing (V in the picture), connect that line U to the backhoe inlet, and connect the backhoe outlet to where I disconnected the U line from (V on the rockshaft). ? Of course using proper fittings, hoses, etc.
I am assuming the backhoe is open center and will allow fluid flow to circulate as it always did before the modification, and I also assume that I will need to attach a jumper line when the backhoe is off from my new connections.
Am I correct, or way off ? I am confused because I am thinking of the backhoe valve stack to be similar to the loader valve and that has a return to reservoir line. Wondering why I don't need that on the backhoe (since there are only two lines)
tractor hydraulics.jpg

Thanks for the help in advance , I have learned a lot from you guys over the years!
Mike
 

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:wgtt:welcome from south western Pa. Mike-i can't answer ur question about the PB -but hold tight till one of the fellas can for sure.
 

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Morning, and welcome to GTT!

I am struggling to read your picture clearly, but in theory I agree that you need to interrupt the oil flow after the SCV and before the rockshaft valve to feed your backhoe. You don't need the third return line in this case since the 3PH cannot be used when the backhoe is mounted.


FYI this drawing is from JDParts and shows the "rear hydraulic lines", which I believe was the PB kit. Note the "pipe plug" #3 that would direct the fluid to the pressure line.



REAR HYDRAULIC LINES

CartkeyPART NO.PART NAMEQTYSERIAL NO.REMARKS
1AR27699Elbow Fitting290 DEGREE
2R26375O-Ring3
315H275Pipe Plug1(POWER BEYOND PLUG)
4AH63063Hydraulic Hose1
5AT54270Hydraulic Hose1
6AT32332Elbow Fitting190 DEGREE, (SUB FOR AR26763)
7R34063Fitting1
819H2676Cap Screw5
9R42009Clamp10
1012H304Lock Washer5
CartkeyPART NO.PART NAMEQTYSERIAL NO.REMARKS
1114H1076Nut5
12AR99077Oil Line1
13AR99378Oil Line1PRESSURE
14AR99379Oil Line1(NLA)
15AR54385Elbow Fitting190 DEGREE
16H33780Tee Fitting1
 

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My question is, using the below diagram from the 750 manual, is it correct to just disconnect the line marked U (PB line at the bottom of the loader valve) from the rockshaft housing (V in the picture), connect that line U to the backhoe inlet, and connect the backhoe outlet to where I disconnected the U line from (V on the rockshaft). ? Of course using proper fittings, hoses, etc. Yes, this is how the PB is connected. It is simply a series connection between the PB of the main SCV and the inlet of the rockshaft lift. You will have to install a jumper hose between the two QC when the BH is not installed.
I am assuming the backhoe is open center and will allow fluid flow to circulate as it always did before the modification, and I also assume that I will need to attach a jumper line when the backhoe is off from my new connections. Yes, the BH valve is open center. You will not need a 3rd tank line because you cannot use the 3 point and the BH at that same time so the rockshaft cannot be pressurized while the BH is attached, therefore, the rockshaft feed, or better said BH return, will return to tank through the rockshaft valve and since the rockshaft cannot be pressurized, this flow feeding the rockshaft valve will simply return to tank through the valve.
Am I correct, or way off ? I am confused because I am thinking of the backhoe valve stack to be similar to the loader valve and that has a return to reservoir line. Wondering why I don't need that on the backhoe (since there are only two lines) See above.
 

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Discussion Starter #6 (Edited)
Hi Kenny and Ray, thanks for the replies. I attached a better picture of the flow diagram (I had the pdf sent instead of a screen photo) in case anyone in the future can use it.

hydraulic system.jpg


Thanks for the parts info, I think that will help some as I couldn't find any info for a kit for the 750. Thanks for the note about the plug, mine must have that since it must be added for any accessories according to this:

hydralic description.jpg


Ray, thanks for the drawing, that is something what I had in mind, I just have to see if I can make that neatly in a good location. Here is my tractor connections I have now. Note the pressure gauge I have in a port, wonder if I can use that port, will have to find the info i had when I put that in a couple of years back

hydraulic picture.jpg


it might be a few weeks before I can tackle this project, but will update when I do.
Thanks, I have enjoyed reading the forum for a lot of info and some humor too.

Mike
 
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