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fed up with 960 hyd top cover

2

2strk2cyl

Member
working on a 960 hydraulic top cover that will not raise. took it apart and found that the unloader valve was stuck, replaced the oring and cleaned the bore and got it working like new. put the cover on and it worked fine. parked the tractor and went out two days later to no hydraulics again. I have now had it off 3 times, the valve has not siezed up again, but now i have found that when i air check the top cover installed on the tractor with the cross over plate off of the top and put air to the pressure in port on the top, it blows back out of the back pressure valve and into the return port without moving the unloader valve or anything else in the system. my question is, what could cause the pressure to go back to the sump? all of the linkage and valving seems to be working corectly other than the unlaoder valve. i feel i am missing something, but i don't know where. i fear i am going to have to pull the cover agian unless someone has some wisdom to help a Deere guy out on this old Ford. thanks alot.
 
(quoted from post at 16:22:20 07/14/10) working on a 960 hydraulic top cover that will not raise. took it apart and found that the unloader valve was stuck, replaced the oring and cleaned the bore and got it working like new. put the cover on and it worked fine. parked the tractor and went out two days later to no hydraulics again. I have now had it off 3 times, the valve has not siezed up again, but now i have found that when i air check the top cover installed on the tractor with the cross over plate off of the top and put air to the pressure in port on the top, it blows back out of the back pressure valve and into the return port without moving the unloader valve or anything else in the system. my question is, what could cause the pressure to go back to the sump? all of the linkage and valving seems to be working corectly other than the unlaoder valve. i feel i am missing something, but i don't know where. i fear i am going to have to pull the cover agian unless someone has some wisdom to help a Deere guy out on this old Ford. thanks alot.
Click to expand...
F the unloading valve does not move to lift position, then the pressure will dump via the back pressure valve...it is the unloader valve spool that stops this flow path. Next question is why unloader won't move properly? May be that control valve spool is not moving far enough into valve body (forward) to open the path for pressure to reach the unloader valve, in order to make UL valve move. May be that BP valve is relieving at such a low pressure that there is insufficient pressure to activate the UL valve. Those are my thoughts for the moment.
 
what should the back pressure valve begin to open at, so i can test the pressure before going through the work of extracting the check valve seat, possibly for no reason. thanks
 
(quoted from post at 07:59:29 07/15/10) what should the back pressure valve begin to open at, so i can test the pressure before going through the work of extracting the check valve seat, possibly for no reason. thanks
Click to expand...
nfortunately, I do not have a hard answer for that. I have not measured it or found it in any manuals, however, on two occasions I have seen people say that it is 40 PSI.....but they could be one quoting the other. George Marsh said he couldn't read anything when using a ~3,000PSI gauge.......which only says that it is some low pressure.
 
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