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No Travel, Rotating Joint removal - Link Belt LS4300 CII

Discussion in 'Excavators' started by iowahill, Feb 6, 2020.

  1. iowahill

    iowahill Senior Member

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    Occupation:
    Retired Union Millwright, pat-time mine operator
    Location:
    Lincoln, CA
    We've finally determined with a slightly uncertain level of confidence that we have an internal seal failure in the rotating joint that is preventing travel on both motors. We couldn't find an easy way to confirm pressures with our gauge setups because of lack access, proper connectors, and/or very stiff hoses that defy much movement. But we DID observe the joint's upper common 1/2" case drain hose jump substantially whenever travel of either or both pedals was activated. This would seem to suggest that the high (~5000 psi) travel pressure from the valve assembly is bypassing internally in the joint and returning to the tank. The 3/8" two-speed hoses to each motor move slightly from pilot pump pressure (~600 psi) when the two-speed solenoid is activated, just as they should.

    So it looks like we have to pull the rotating joint out to check and reseal. How does the assembly come out? From the top or bottom? By itself or with the cone shaped outer housing?
    That assembly had been removed and resealed in 2011 not long before the machine was idled until 3 months ago. Though the job of resealing was done by a reputable hydraulic shop the failure may have been because of sitting for so long without operation OR when the hydraulic oil ran low at one point a short time later.

    All pressures are good and within spec, and there are no external leaks. Anybody out there who has pulled one of these out and can offer some tips and guidance? Thanks, -Tom
     
  2. Dave Neubert

    Dave Neubert Senior Member

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    normally you will still be able to travel just weak did you pull the case drains from the motor side to see if increased flow is coming from the motors or the swivel also will it counter rotate it will normally counter rotate even with bad swivel.
     
  3. iowahill

    iowahill Senior Member

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    Retired Union Millwright, pat-time mine operator
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    Thank you for your reply Dave. No, we didn't pull the case drains and there is just the slightest load felt when applying travel to either or both motors. Because of the time this machine has sat and the amount of dirt accumulated it's going to take a lot of power to get it to move. It was driven over to where it is about 8 years ago, then parked because of other problems, not the least of which was a badly worn pilot pump which we replaced 2 weeks ago. The loss of travel reportedly occurred some time after it was parked for other repairs.

    All functions including Swing work normally. The amount of jump exhibited by the single upper case drain line looks like a lot of high pressure fluid is being bypassed back to the tank.
     
  4. Dave Neubert

    Dave Neubert Senior Member

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    That is why I would pull the case drains at the motor if it is the swivel oil would flow from the hoses if it is a travel motor problem it will flow out of the motors. I have had them travel even with seals blown out. will the track try to move if you jack it up off the ground. and have you put a gauge on the pumps to see if you are building pressure in travel mode
     
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  5. Mike85

    Mike85 Well-Known Member

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    It's worth checking your case drain coming from the motors at motor. If a motor is bypassing internally it will also give you high case drain on the top of the rotary like your describing seeing
     
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  6. iowahill

    iowahill Senior Member

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    Being in unfamiliar territory with this troubleshooting issue my answer to your questions is no. Are the case drains via the hose or is it one of the Allen plugs on the motor housing itself? I thought about pulling one of the case drain hoses off and putting my gauge on the hose end while plugging the motor port, then reversing the procedure to check pressure on both sides of that line. It's unlikely (but not impossible) that both motors would be bad as there were no previous problems with travel reported.

    You comment about swing/swivel oil perhaps getting into the case drains is an interesting thought, so I'll check that out. I just thought about raising one track off the ground with the boom and testing to see if we get any movement, so will give that a try too.
     
  7. iowahill

    iowahill Senior Member

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    Thanks MIke. We'll give that a try when I go back up on the weekend. The machine is well off the grid in what I like to call "the banana belt".
     
  8. iowahill

    iowahill Senior Member

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    Just to be clear... I'm guessing that we measure our pressures at the top and bottom test ports on the pump, correct? And do we pull the case drain hose to look for bypass oil when we try Swing, or is there a plug on the motor
     
  9. iowahill

    iowahill Senior Member

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    I just found the section of our Service Manual that identifies the test ports on the travel motors. I just need to grab a couple of 3/8" pipe test fittings then should be able to make sense of our travel problem. Thanks Folks!
     
  10. DK88

    DK88 Senior Member

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    you can just pull half the joint and reseal it and drop it back on.. saves a few hoses and bolts.
     
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  11. John C.

    John C. Senior Member

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    While two bad travel motors is possible, it is more unlikely than the swivel seals leaking.

    There is another big possibility though in that the CII machines were well known for the two speed shift pistons in the travel motor to leak through and leave the motors permanently stuck in high speed travel. I would pull the swivel apart first and reseal to eliminate that as a possibility and proceed from there if the problem persists. The swivel is relatively easy and less expensive than chasing travel motors just yet.

    To check case drain on any motor you don't need gauges. Just remove the case drain hose from the motor and cap it. Now hook up a second hose to the motor and run the open end into a bucket. Now you have to keep the motor from turning somehow, pin in the sprocket teeth usually and then operate it to relief pressure. Most motors that are good will get about a pint in about a minute.
     
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  12. iowahill

    iowahill Senior Member

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    Occupation:
    Retired Union Millwright, pat-time mine operator
    Location:
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    I finally heard back from the previous operator that the machine was never started after the rotating joint was resealed in 2011 due to numerous other problems, mostly neglect. We finally got the problems narrowed down to a badly worn pilot pump (original equipment), so we pulled and replaced that pump only to have the new one go bad after about 30 minutes of operation.

    Yes, we made sure we had the tank and lines clean before refilling the 55 gallons of new hydraulic oil, put in a new pilot filter element, and had good pressures and swing until we lost pilot pressure once again with the pump failure last week. Lots of fine particles in the pilot filter confirmed the pump went bad.

    I've worked turbine overhauls at refineries and know my way around keeping things clean around pumps and high pressures. I noticed that the new pump didn't turn by hand when I got it, and using pliers to assist I could feel engagement of each tooth as I turned it. As I wasn't familiar with this particular pump I assumed it was normal given the $780 price it took to get it.

    We're going to pull the pump out again tomorrow, then take it to my shop to tear it down for inspection and confirmation. I noticed that when we hooked our gauges up to confirm loss of pilot pressure that we now didn't have the 5000 lb pressures off the two main pumps like we did with the old pilot pump. At full throttle those pressures only climbed to about 1000 lbs. Perhaps there's a governing valve in the main pump body controlled with pilot pressure?

    I'll know more in a couple of days. Thanks to you folks for the tips and help. Fortunately, we don't have to deal with the rotating pump!
     
  13. John C.

    John C. Senior Member

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    That system does use pilot pressure as part of the control pressure on the main pumps. PM me an email address and I'll send you what little information I have on that model of Link Belt.
     
  14. iowahill

    iowahill Senior Member

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    Retired Union Millwright, pat-time mine operator
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    Will do John. I'm concerned that the new pilot pump which had over 1200 psi pressure when first installed before adjusting relief pressure to around 600 psi would go south on us. Installation was simple, and it came with new O rings and the two mounting screws. All functions except for travel seemed good, so we were suspecting a problem with the rotating joint until last week when we found out that the machine was never started after the resealing job. I'll try the PM now.