Bobcat x231 excavator. Left track, boom and arm functions stopped working completely suddenly at the same time. Right track, bucket, swing, blade, aux, all still working fine. Hydraulic fluid and filter is clean. Hydraulic pilot system, no electronics. Would appreciate any input where to start looking. I have checked the main relief for the left track, reliefs for boom, reliefs for arm and check valves on aux. All appear to be fine. I have swapped hoses around on the 3 stage pump and it does not change anything. I switched the lines off the left track spool and put them onto the right side spool and the track works good but then lose the right track and still don’t have arm or boom. The manual states the left track, arm, and aux are all fed from pump 2 (middle pump). I have pulled off the pilot lines and manually pressed the spools that are inoperable with a screwdriver and still nothing. I do not have a control pattern selector valve. I do have a aux selector valve.
I also capped the left track lines and tested for back pressure at pump test port and get nothing.
Losing left track, boom, and arm simultaneously with no back pressure at the pump test port = pump section 2 (middle section) has catastrophically failed. Because: Manually pushing spools = nothing (rules out pilot system) Swapping lines moves function to different spools = main valve is fine Zero back pressure at pump 2 test port = pump not generating flow/pressure All failed functions fed by pump 2 per manual = confirms pump section failure What failed in pump 2: Internal gear damage (stripped teeth, broken shaft) Seized bearings causing shaft breakage Coupling between sections sheared Why it happened suddenly: Catastrophic internal failure (gear tooth broke off) Drive shaft/coupling failure between pump sections Contamination locked up that section Next steps: Remove pump, disassemble pump 2 section - you'll find obvious mechanical damage Check for metal contamination in system - whatever broke will have shed debris Full system flush required before installing rebuilt/replacement pump The fact that you get zero pressure/flow from pump 2 but sections 1 and 3 work fine confirms an internal mechanical failure isolated to that section. Don't waste time on valves - it's 100% the pump.You need a pump rebuild or replacement and system decontamination.
When I swap the out put of pump 2 with pump 1 or 3 I receive back pressure on pump 2 then. Whatever functions I still have working (bucket, right track) I can put onto pump 2 and they work.
Would be nice to flow check your pumps.
So I’m getting good flow out of pump 2. When I pull the pump 2 inlet line off at the valve body I’m getting more fluid squirting out the inlet than I am coming from the pump 2 line.
I pulled the pump and had it taken apart and inspected. They said minimal wear if any and everything is in good working order.
Install pressure gauge directly at pump 2 outlet (before valve), Command boom/arm/left track, If pressure is low (under 500 psi) = internal valve bypass, If pressure builds (2000+ psi) = blockage preventing flow to spools. Does your machine have Priority/divider spool? Please drop schematic if you have. If there's an internal priority element for pump 2's circuits, it could be stuck closed.
I installed the gauge on pump 2 and don’t get any reading. Could this be an issue with my swivel joint? I’m running out of things to check it seems.
Ok, First of all whoever made this schematic has no idea what's he has built. Return line and suction line is combined by part 7 which shouldn't be. Now for Left Track: You said: [ I switched the lines off the left track spool and put them onto the right side spool and the track works good but then lose the right track and still don’t have arm or boom. ] I want to know from where did you switched the lines? MCV (29) to Rotary Joint (3) or Rotary Joint (3) to LH Track Motor (2) This will help us to eliminate entirely looking at MCV and focus on Rotary Joint. Now for Arm: Since you said, your Aux is working fine, meaning flow from P2 Pump is good because P2 support LH Track, Arm & Aux. Now let's check MCV (29) sequence wise 1. Check Inline check valve, if is it stuck 2. Now since your Arm is actuated by pilot, we have to check pilot actuation. 2a. Joystick (25) is receiving flow from Pressure Maintenance Valve (21) which is receiving flow from Pump P1 / P3 whichever gives more pressure. Since your bucket is working fine, which is getting pilot signal from joystick (26) which is receiving flow from Pressure Maintenance Valve (21) - this conclude that Pressure Maintenance Valve (21) is doing it's work. 2b. This conclude that PMV is good, so let's check Joystick (25). Since you said your swing function are working fine meaning joystick is working fine in giving pilot signal. Check pressure on port 2/4 (whichever way you actuate your swing) - note it and then check pressure on port 1/3 (whichever way you actuate your arm) - note it and then check pressure curves for joystick and verify it's sufficient. if not, your joystick is causing the issue. Note: This is rare case, joystick issues are rare. 3. Temp. Swap Aux Line to Arm and check if the issue still there 4. Does your both retraction and extension of arm is affected or just one? If both then i suspect the Arm spool. Since your Arm cylinder is cushioned both side, i would compare actual vs speed mentioned in manual. Test Flow: Swap Lines from Aux to Arm > Check Inline valve > Check Joystick > Check Spool > Check ARV Pressure > Cylinder. Check similar way for boom too. Hope this gives you a way. And yeah, do tell what's the displacement of your tandem pump. @Vetech63 might provide detailed analysis.
Post pics of your pump set up....all of it. The more detailed the pics are the better.
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So you have a 3 section gear type hydraulic pump. It already has the test ports for each section. You now need to know what each section operates to make sure your pressure gauge is plumbed into the correct pump section for what function you are troubleshooting. Plumb your gauge and bottom out the faulty implement....what does the gauge read? Gear pumps can have internal leakage from housing wear or end plate orings blowout.
I get no reading at all. When I connect pump 2 to the opposite side of the valve body (P1 inlet) i can get a reading. No matter which section of the 3 section pump I connect to that P2 inlet on the valve bank I get no reading. I already had the pump taken off and took it into a shop. They said pump looked great and showed no signs of wear.
I posted above the pages from my service manual stating what feeds what also. Pump 2 is feeding aux, arm, and left track. Arm does not work at all and left track does not work at all. Aux does work but is controlled by 2 pumps according to the manual.
The pump 2 output line should go to a control valve. Follow that line and take a pic of that control valve. Post that pic
Find #27 . That would be the main relief for that control section. Remove it and see if there is anything stuck in it or broken.
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I have pulled the main reliefs on both sides taken them apart and inspected them and both are good. No signs of any damage.
Did you try swapping them?
The reliefs are different and would not fit so no I can not swap them.
Your hydraulic legend is specing them identically. Now I'm concerned you are not looking at the right reliefs . Are you positive you are looking at both main relief valves and not port reliefs?
Right track P1 main
Left track P2 main
I also did go through all of the small port reliefs and checked them.
What sucks about this is i cant be there and trace lines with my own eyes. Im depending on pictures and trying to compare them with the hydraulic schematic is proving to be difficult. Each pump section is putting out 9gpm which is pretty good flow at full engine rpms. The outlet on that part of the control valve should be putting out the same gpm. If you are getting nothing on the arm at all, I would think whatever is bypassing the fluid would have a severe flushing sound at 9 gpm. Even though the main control valve is one body, the flow through it is separate depending on which pump feed its attached to. Have you had someone near the control valve listening while you work the faulty functions? Bypassing oil that bad should also create heat quickly. Have you checked areas with a temp gun,?
I totally get where you’re coming from and I do agree the schematics are terrible. I appreciate you taking the time to help. That’s what’s been so bizarre about this whole deal is that when you work the functions that aren’t operable you hear absolutely no change in rpms, no fluid sounds etc. the only function that you can barely hear a fluid sounds etc is when you try to operate the boom function. I’ve been told by a few local equipment mechanics that the only thing that could really be bypassing that much fluid would be the swivel joint but I have yet to find any way to perform a diagnostic on that.
For left track: where did you swap your hoses?
I swapped them on the valve bank. Took the 2 hoses off the left track spool and swapped them with the 2 hoses on the right track spool.
This means your Rotary joint is fine. check your LH track spool in MCV. after swapping lines does your LH motor have sufficient rpm on full throttle?
Yes. I had the left track spool pulled and inspected 2 days ago and it was in great shape.
Still trying to solve my issue. I’ve gained some traction. So since I last posted I have resealed the swivel, went through the whole 6 spool valve again, and now I realize as soon as I start the machine it is blowing the oring/backup off the main relief for P2. Now just need to figure out why. Only things downstream from the p2 relief on the return side is the auxiliary selector valve, oil cooler, and the filter which I have replaced twice.
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Good Progress. From schematic check out where P2 line connection joined, check out for restriction.
Finally got it fixed. First I found the boom cylinder piston had spun off the rod, that would have been the original issue the previous owner had been chasing. In the process of looking for that issue when they had the valve body taken in to be inspected This little block off plate was removed by One of the shops that had the valve body apart didn't put it back then causing 0 pressure on half of the 6 spool valve and losing left track, and arm. Had the local machine shop make one on the water jet and all is well. Thanks for all the help. Nothing worse than working on stuff other people have already dug into. Luckily I had the 6 spool valve body apart for the second time and could notice some minor scoring from the previous block off plate.