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.
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Bobcat X231 lost multiple functions I am at a loss
- Thread starter Branstor
- Start date
nikthewho
Well-Known Member
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:
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
- Internal gear damage (stripped teeth, broken shaft)
- Seized bearings causing shaft breakage
- Coupling between sections sheared
- Catastrophic internal failure (gear tooth broke off)
- Drive shaft/coupling failure between pump sections
- Contamination locked up that section
- 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
nikthewho
Well-Known Member
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.
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.
nikthewho
Well-Known Member
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.
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.
Attachments
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.