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Discussion Starter · #1 ·
I have a John Deere 955 with just over 500 actual hours. When I bought it a few years ago, I changed the engine oil and hydraulic fluids since I didn't know when they were last changed. I’ve worked on John Deere 855’s before and grew up with a lot of mechanical experience working on my family's farm. I'm a bit embarrassed by it, but I mistakenly removed one of the pressure relief valves underneath the hydraulic oil filter thinking that was the drain plug. At the time, I didn't have an operator/service manual and thought I knew what I was doing but in hindsight, I should have gotten my hands on an operator/service manual first. I reinstalled all the components of the pressure relief valve as I found it, found the proper drain plug, and fully drained the hydraulic system. I also cleaned the screen in the hydraulics back by the rear PTO. I used a new JD hydraulic filter and refilled the system with the proper JD hydraulic fluid. Ever since that hydraulic oil change, my hydro transmission doesn’t seem to act correctly. When going down a minor grade hill in both lo and hi, at both slow and fast speeds in the forward direction, the hydro goes in what I would call coast mode where the hydro feels like it isn’t trying to propel the tractor anymore and almost sounds like it is sucking air. The tractor then slows down a little bit when I'm going down the grass covered grade and then the hydro suddenly kicks, giving a sudden jerk similar to what it would feel like when stopped and suddenly pushing the forward hydro pedal suddenly halfway down, and the tractor goes back to the original speed. Also when at a stop, if I push the forward hydro pedal down slowly, the tractor doesn’t immediately move until I get to a certain point and then it jerks and takes off. The going down an incline issue and moving from a stop issue happens at both an idle engine rpm and at full throttle. I’ve also noticed when parking the tractor and shut it off in my garage on an ever so slight of a cement floor grade/incline without the parking brake on, the tractor will try to roll out my garage unless I put the parking brake on (I know - you should always put the parking brake on, but typically you don't have to on such a small grade). If I’m in high transmission and going a decent speed and release my foot off the hydro pedal, the hydro sounds like it is sucking air. I understand the hydro will make a winding down noise but this noise is a little different than that. I also hear it in low transmission but it isn't as apparent.

This tractor had none of these issues until I changed the hydro fluids, the hydro filter, and I mistakenly removed the wrong plug. My father, brother, and two uncles own JD 755’s/855’s and none of them behave this way so I know it isn't typical behavior. I unfortunately am not 100% positive which one of the two pressure relief valves I removed directly underneath the hydro filter. I’m 90% positive that I removed the pressure relief valve plug that isn’t recessed in the housing. Since I was fairly confident this plug was the one I removed, I pulled the plug and verified against a part schematic that all the components are there (I was afraid that maybe I accidentally dropped a small piece of the assembly and missed it on the reassembly but that was not the case). I then drove the tractor around for awhile and confirmed the hydro behaved the same way. I then pulled the pressure relief valve next to it that is recessed in the housing and verified against a part schematic that all the components are there (again, all the pieces of the assembly were found to be installed). I then drove the tractor around for awhile and confirmed the hydro behaved the same way. It started to make me wonder if maybe one of the o-rings on the two pressure relief valves were leaking causing air to get into the system so I changed the o-ring on both pressure relief plugs and still have the same hydro issue. I have also fully drained the oil and verified the screen is not plugged and made sure I had the system filled to the proper fluid level. I have also checked the hydro system pressure at the hydro quick disconnect fittings and all appears to be fine. I have also verified the hose clamps on the hydro suction line are tight. The only other thing I can think of doing next is to change out the entire pressure relief valve but they run around $100 and I’m not sure if that will fix the issue. I was wondering if anyone had any other thoughts on what might be the issue and how to fix it.

Thanks,
Randy
 

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Do you have the 955 Repair manual?
 

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Discussion Starter · #3 ·
I unfortunately do not. I found one online a few months back and skimmed through it to see it would help me troubleshoot the issue. I confirmed my hydraulic pressure was ok. If I recall correctly, some of the other checks I didn’t have the proper tools to perform the checks myself
 

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I spent some time this morning reading through the service manual. There's not a whole lot of information regarding the main relief valve/check ports, or the charge relief valve. But most of the troubleshooting guide points towards the valves if there is a problem; though erratic behavior is not listed. Checking for parts to slide freely, no damage to spring seats and valves, ect...I can't find any torque spec though. Is it possible to have lost shims while removing? That would change the relief pressure.

-Aaron-
 

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Randy, Except for removing the relief valves, everything you did preforming your oil & filter change is normal and wouldn't give you any problems. I'm saying "something" (??) with the relief valves and most likely the first one you removed. Although kinda difficult to tell from parts diagram, on valve appears to be a ball check and the other a poppet type relief so they're not interchangeable. Remove it again, inspect for free movement, and try again! Sorry I can't help more, Bob
 
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Discussion Starter · #6 ·
I appreciate everyone’s input. When I get a chance, I will have to take it back apart and look into it further. I don’t think there is a shim on my pressure relief valve. I don’t see how I would have lost the shim though because based on the assemble print, the shim appears to be between the spring and the threaded plug. The spring stayed on the plug so I don’t think the shim would have been able to fall off and into the oil. Everything went/slide together very smoothly by hand and the assembly threaded in most of the way by hand. I agree it seems to be directly related to my mistake of pulling the pressure relief valve. I’m attempted to buy a new pressure relief valve but it unfortunately doesn’t look like the pressure relief valve P/N AM103612 is available anymore ☹

Thanks again for everyone’s input. If you think of anything else, please let me know
 
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