Case 680e hydraulic bypass

Bean5690 · Nov 23, 2019

Hello all new to the forum first post.
I have a case 680e 1974 a ck it s new to me and bought it with nonfunctional hydraulics. I have purchased the manuals for it and have been doing all the research I can about it. The steering/stabilizer circuit works I can drive it around the problem is with all the other functions. I have proved flow.... kind of redneck into a bucket and started it up but none the less it is moving oil on that circuit. It won t however build pressure i have a gauge hooked up to the test port t on that circuit and don t get anything so it seems like a straight bypass to me although I m not a professional. I have removed/ cleaned the main relief valve on the loader controls it didn t help. Wondering if anyone has any insight into how else it could be bypassing. There is a soliniod on the back of the loader control which I believe is for return to dig? Also read about the tilt stop if you lift the bucket high enough and try to tilt it back it s supposed to stop. Kind of a long winded post for my first one wanted to give as much info as possible right off the bat, it was sitting a long time before I got it and apparently was working a couple months ago.

Case Nutty 1660 · Nov 24, 2019

So you have a Case service manual on it or just a ops and parts book? there is a test in the SM to walk you through this,, sounds like relief is stuck open,, this can be in the backhoe valve also,, the electric solenoid on the loader valve is for the bucket curl detente it controls both bucket level and to kick out detente at "level bucket/return-to-dig position" point like you are thinking,, if you have a IT or some aftermarket SM I doubt it will be much help for this problem,, my 680E SM does have these steps in great detail is why I am guessing you do not have the manual you need for this repair/diagnosis, congrats on the purchase we sold a lot of 680's the last Series being a 680E I loved them so much I bought one a couple years back, they also have a air pressured hyd tank to keep Full oil flow to the pump,, but even with no air tot he tank you will have all functions it will just not regenerate as fast as its supposed under full digging power
cnt

Case Nutty 1660 · Nov 24, 2019

I did some looking in my SM and refreshing myself with the 680E hyd system,, I am now thinking you may have a pump issue as they use a two part pump, one section does steering and diverts oil to the backhoe stabilizer valve,, I will make a educated guess the main part of the pump drive couple is worn and slipping, but still drives it enough to make oil free flow out the open hose where you tested it,, that is why you have steering and stablizers function
cnt

Bean5690 · Nov 24, 2019

Thank you for you response I do believe I have the correct service manual .... I have all 3 the service manual is like 700 pages I ve found relief adjustments and that in there never seem anything about checking for a stick relief valve. It shows first about using a flow meter which I don t have because they are pretty expensive then goes into pressure tests which I have done at the test port like they show. I have removed and cleaned the main relief valve and reinstalled. I believe the backhoe relief valve is on the other circuit if you reference a page from the book or the test so I can try to find the one you are talking about the manual is as far as I know a reprint of the original for eBay. Also if the power beyond can be blocked off without damage to the pump just to isolate section to narrow down the problem. Yes the tank is pressurizing with air but like you say shouldn t hold back all functions. Thank you again for your quick response

mEl · Nov 24, 2019

- Did u remove the inner spring and the plunger behind it in the main relief? The valve is a compound relief in that it uses a needle and seat to control a larger piston inside the body in that same bore. The inner piston has a tiny orifice drilling that must be open and the screen on the large piston must be clear.

Bean5690 · Nov 24, 2019

MEI yes now that I have looked at the drawing the larger spring is the one I missed though. It didn t come out with the piston part so thank you for mentioning that I will take it out again and see if I can get the larger one out. I didn t take the plug side of the relief valve out thinking the adjustment was the only part that could be a problem
Case I haven t ruled out pump malfunction yet either was trying to hope it could be an easy fix.... yes you are correct it is all the things on the steering side of the pump that work. I m toying with the idea of swapping the hoses at the pump since I know the other side works it will prove it both ways 1 by the other side of the pump operating the steering and stabilizers 2 by the side of the pump I know is working still not getting pressure on that side . Or of course it doesn t work the stabilizer and I know the pump has to come out
Thank you both for your help

Case Nutty 1660 · Nov 25, 2019

mEl, has far more hands on work on a 680E than I do,, they were new last one we sold in 1975 or 76,, and we had zero repairs on any before we sold out in late 76,, the pump may or may not be your issues,, I have found after all these years when something is not working right I have to look at every part when I take it apart and more times than I can count they were assembled wrong, I was just going off the issues you spoke of so I call it a educated guess lol I need to get started rebuilding my 680E been looking for the correct spanner wrenches to do all the cylinders,, but so far no luck,, I may have to use the adjustable one I bought years ago off the Snap On truck,, mine has lots of problems,, but I am hoping I can get it done before I am not here any more.. a flow meter would be handy for me to nail down you issue,, but not everyone has one, I do not use mine a lot but when I need it it sure comes in handy
cnt

mEl · Nov 25, 2019

I agree CN, a flow meter takes the guesswork out of it, a simple T test will show any fault in the many circuits if you know how to test. A bad pump is a real possibility but I would make sure the internal poppet in the relief valve is clean and free in its bore, simply because it is easy and I have seen issues as that style relief was also used in the 530- 580 hoes and loaders and we serviced many of those over the years.

Bean5690 · Nov 25, 2019

Ok that s great I will get into that relief valve as soon as I can to try to rule that out. Would swapping the hoses at the pump be a viable option? I know they are different gpm but could possibly identify the problem since I don t have a flow meter. I m not really well versed in hydraulic pumps but if I have some kind of flow I would think it would eventually build some kind of pressure unless it s bypassing.

Bean5690 · Dec 5, 2019

So an update I ve tried to take the main relief valve apart again I ve got the bigger spring out but could not get the poppet and seat and the other stuff out. There is a plug on the top side of the loader control with an Allen head on it I don t really have access to while it s still installed. I have found someone that is able to borrow a flow meter from someone else so I can know for sure whether it s the pump or not. In the service manual they have the tests to run laid out but I am a bit confused as far as how this meter is hooked up it is isolated from all the systems.... at least the way I see it the t is capped and ran right back into the tank. Having never used a flow meter before and will only have it borrowed for a short time any advice or particular tests I should conduct. Of course I will check flow both free and under load from the valve on the meter but the book describes other tests to check for relief valves and cylinder bypass is the hook up the same or does the system have to be tied back together first. Also not sure if some of these tests will require a more functioning system to diagnose individual issues. Thanks for the read any info is greatly appreciated

mEl · Dec 5, 2019

(quoted from post at 02:22:53 12/05/19) So an update I ve tried to take the main relief valve apart again I ve got the bigger spring out but could not get the poppet and seat and the other stuff out. There is a plug on the top side of the loader control with an Allen head on it I don t really have access to while it s still installed. I have found someone that is able to borrow a flow meter from someone else so I can know for sure whether it s the pump or not. In the service manual they have the tests to run laid out but I am a bit confused as far as how this meter is hooked up it is isolated from all the systems.... at least the way I see it the t is capped and ran right back into the tank. Having never used a flow meter before and will only have it borrowed for a short time any advice or particular tests I should conduct. Of course I will check flow both free and under load from the valve on the meter but the book describes other tests to check for relief valves and cylinder bypass is the hook up the same or does the system have to be tied back together first. Also not sure if some of these tests will require a more functioning system to diagnose individual issues. Thanks for the read any info is greatly appreciated

The pump can be disconnected from the system and the flowmeter put inline between the pump and tank but his test has to be done carefully as there is no relief and pump damage could happen if the pump pressure is taken above the pumps limit, 2000 lbs is enough to test the pump for leakage, the pump should not vary more than 20 percent cold oil to hot oil.

If you cannot remove the poppet in the valve housing you may have found your problem, get a piece of wooden dowel rod bigger than the poppet and grind a taper on it to wedge in the poppet to pull it out.

A Tee test is just that, a tee is put into the pressure line just off the pump often the pressure test quick coupler can be removed and the test hose connected there and the flow meter with the flow meter return flow back to tank. setting the flow meter pressure just below main relief and working each system will show leakage in individual circuits, with my flow meter I could pick up 1/2 gpm leakage in a 45 GPM system, A flow meter is invaluable and I'm glad you have access to one. center around getting that poppet out right now and I know of no access to it but have never had to as even if stuck I have always been able to get them free.

mEl · Dec 5, 2019

The Tee test assumes a functioning system, if the pump looks good you are almost guaranteed to be looking at main relief, looking at the hydraulic layout in the service manual it appears that the loader relief controls the whole system, things can happen to cause a good loader and faulty backhoe operation.

Bean5690 · Dec 5, 2019

MEI yes it will be good just to confirm that it is not the pump and both sides are working as they should. With getting the poppet put does it come out for the same side as the spring is there anything that needs to be addressed from the top side with the Allen head plug in it that could be a problem? I will try the dowel trick and hope to get it out that way. Thanks again for the info

mEl · Dec 5, 2019

The poppet should come right out easily once the spring is removed. it should slide easily in the bore with no tight spots. as far as I know there is no access to that bore from the opening you describe but I have never tried it as I didn't need to.

Bean5690 · Dec 16, 2019

I wanted to update you guys that I did manage to get the backhoe working. I still wasn t able to get the poppet out even using the dowel but I guess I freed it up while trying I now have all functions back. Now I have some cylinders to repack and other maintenance to catch up on with this old machine thanks again for the help

Case 680e hydraulic bypass

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