853H Low Hydraulic Pressure Problem

[4x4 Nut]

Hello all, I have a 853H with about 3500 hrs. that's pre BICS (PIN #512815269). The hydraulic system has been getting slowly weaker over the last few months & here recently really bad. I installed a flow meter w/ gauge on the axillary output & found the volume is good (20+ GPM), but when I close the valve, the pressure is about 1300-1400 PSI & when left deadheaded it drops off about 100# every couple seconds. After the machine has run a little bit & warmed up some the pressure will only hit about 700#. Obviously this is causing a very weak bucket operation. The drive works fine at all times (both sides) & the belt tension seems good so I'm sure it's not belt slip. I've installed a new pressure relief valve & played with the adjustment of it with no real change. Then installed a new hydraulic pump & still the same (new pump actually has slightly less volume output). The reservoir was removed & I didn't find any blockage or even shavings in the system. Both hyd. filters have been changed. It about has to be something in the valve block(s), but not sure what. Has anyone every experienced something like this or have a suggestion as to what to look at? Thanks a lot for any help. Have a good one.

 

[Tazza]

You may need to check your relief, something may be stuck between it and the seat. It should be screwed into the control block.

 

[4x4 Nut]

Well we got it taken care of. Turns out the H has 2 hydraulic relief valves. Where the relief fits the valve body on the 853, there is a special fitting with a hydraulic tube that feeds an auxiliary valve body on the 853H- located under the seat to the left (as seated). The relief valve is then remote mounted in the 2nd valve body & that's what I first changed. After that & the replacement pump didn't help, I got to studying the hydraulic schematics & found there is also still a relief valve in the standard valve block where the jumper tube attaches. It's not just a fitting for plumbing to the 2nd valve body. Almost $500 just for that relief, but fixed the problem & works great now.

 

[Tazza]

Well we got it taken care of. Turns out the H has 2 hydraulic relief valves. Where the relief fits the valve body on the 853, there is a special fitting with a hydraulic tube that feeds an auxiliary valve body on the 853H- located under the seat to the left (as seated). The relief valve is then remote mounted in the 2nd valve body & that's what I first changed. After that & the replacement pump didn't help, I got to studying the hydraulic schematics & found there is also still a relief valve in the standard valve block where the jumper tube attaches. It's not just a fitting for plumbing to the 2nd valve body. Almost $500 just for that relief, but fixed the problem & works great now.

I never knew there was a second relief, it seems it was made of gold though.... Glad it's fixed though, good to know to look out for it if i ever see that issue.