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Please tell me I did't just fry my bobcats hydraulics!!

Discussion in 'Skid Steers' started by jav, Feb 9, 2013.

  1. jav

    jav Well-Known Member

    Joined:
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    MA
    I have a 1986 bobcat 843. I was cleaning up snow (blizzard of 2013) and it was working great! Used it for about 4 hours without problem. My neighbor came by and asked if I could move a plow pile for him- I had done a bunch already so i drove it down to his place about 800 yards down the road- did the pile- no problem, then I was just dressed things up a bit...real light stuff compared to the plow piles.

    Then it happened - As I lifted a small pile over head to dump , I tilted the bucket down and as I went to pull back and tilt it back up, the tilt didn't work and the reverse was real noisy. I shut it down immediately it sounded that bad. The bucket was still raised and tilted down. I checked the hydraulic oil and it wasn't even showing on the dip stick. Walked home- got a gallon of Hydraulic oil (not bobcat) and it took 3 quarts to get back within the lines on the dipstick.

    Started fine and it does move but I have no movement in the tilt and lift cylinders! I was able to let the arms come down via gravity and tilted the bucket back using the the ground and reversing but I have no hydraulic power for lift or tilt- NONE. Even moving doesn't seem right! makes much more noise and it seems to pull to one side!

    Did i just fry my hydraulics? BTW- fluid and all filters were changed less than 50 hours ago (with bobcat brand).

    HELP- is there a bleed process or something I can try?

    Thanks in Advance...feeling dejected.
     
  2. KSSS

    KSSS Senior Member

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    The pump may be out, but it may not have anything to do with low fluid. Having the bucket up in the air may have caused you to show the machine being low on fluid, a gallon low typically wont cause a problem. Your pump may be out, but I doubt it was due to low oil level.
     
  3. crewchief888

    crewchief888 Senior Member

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    off the top of my head,
    is your RH sterring lever pushed off to the cage side of the machine. ie: aux engaged?
    if the drives are not weak,
    the coupler between the hyd pump and hydrostat could have broken.
    if the drive is weak, the pump coupler/ujoint may have stripped or broken

    :confused:

    :drinkup
     
  4. jav

    jav Well-Known Member

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    I've gone out 3 times to see if perhaps there was an air pocket keeping the pump from priming- no go.

    To anser some questions- auxiliary hydraulics aren't engaged. I did try it both ways just to be sure and there's no audible difference either way - ie.. no pressure built up.

    I've been staring at the hydraulic diagram... am I correct in thinking there's 3 pumps? One for each side of the drive wheels and one for the tilt and lift? Also the pressure relief only works for the lift/tilt/aux... correct?

    I brought the machine home (800 yards) and now I'm really worried... one side isn't driving well at all. Looking at the parts break down, it looks like there's a coupler between the front and rear drive pumps and If that coupler went, it looks like I'd have drive to one side only and depending on how it broke/stripped it might allow the other side to drive if the load was low. And it would also prevent the hydrostatic pump from spinning.

    Is this likely? How big a job?


    How the heck could everything have gone so wrong so fast? Everything was literally working perfect one second, then no lift/tilt all all next second PLUS drive problems???
     
    Last edited: Feb 9, 2013
  5. big ben

    big ben Senior Member

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    Next step if you have noise and hyd issues is to remove and cut the hyd filter. Cross your fingers it is clean and not full of metal. I would not run it any more until you check the filter condition.
     
  6. jav

    jav Well-Known Member

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    I have 2 filters- hydraulic and hydrostatic. Looks like I'll be cutting both.
     
  7. Hendrik

    Hendrik Senior Member

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    I have bugger all experience with bobcat setups but my ASV has three pumps, two for drive and one for the loader arm and aux hyd.
    Perhaps a relief valve is stuck open?
     
  8. jav

    jav Well-Known Member

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    I think that would explain the lift tilt but not the drive problem (I believe??). I think the relief valve is out of the loop on the drive side. Also- I think is would see some movement on lift tilt eve with the relief valve open? I get nothing, nada, zip... not even a wiggle in a cylinder.
     
  9. crewchief888

    crewchief888 Senior Member

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    yes there are 3 pumps, all inline
    rear pump is left side drive, next is right side drive, then (if i recall) a gear pump for hydraulics,
    what side drive is weak?
    do you feel a strange "seat of the pants" vibration that wasnt there before?

    as for why all of a sudden........

    unit is 26 years old, nothing lasts forever unfortunately :(

    :drinkup

    BTW the 843 is my least favorite machine to work on.....
     
  10. jav

    jav Well-Known Member

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    thanks for that! I've done so much to it already, about the only thing I hadn't rebuilt was the hydraulics.

    it's the left side that's weak (my left while sitting in it). Rear pump is the one closest to the engine?

    Vibration? you could call it that but it's more associated with noise. At full throttle without any hydro demand- there is no vibration. if you move forward or back slowly (half throttle) not much noise- no vibration. Try pivoting or turning (forcing one side to skid) and the noise and vibration are very obvious.
     
  11. crewchief888

    crewchief888 Senior Member

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    the 1st thing i'd check would be the pump coupler/ujoint, between the engine and pumps...

    :drinkup
     
  12. jav

    jav Well-Known Member

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    so pull the engine? Aw man! I was hoping for something a little less invasive.

    if it was the coupler... wouldn't I lose all drive? I still have reasonable drive on one side.
     
  13. Bobcatdan

    Bobcatdan Well-Known Member

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    I'm wondering if your gear pump is shot. It provide charge pressure to the hydro pumps. I'm think left was weak to begin with and is more noticeable now with low charge.
     
  14. jav

    jav Well-Known Member

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    that makes sense but I've never seen a pump fail like this. I've seen them get weaker and weaker over time. This one was strong enough to lift a heaping bucket of wet snow one second and then not even be able to budge an empty bucket. It was like something suddenly broke.

    The inter-pump coupler would make sense if it drove the left wheel pump and gear pump but not if it drives the right wheels (they are still fairly strong) and gear pump (as cheif suggests). Same with the main coupler- I would think if that went, I'd have hardly any drive either and mechanical noises (coupler slip- if it was able to drive low loads).

    Is there a coupler for the gear pump alone? I don'e see one on the parts diagram.

    Could a wide open relief valve cause weak charge pressure and absolutely no cylinder movement?
     
    Last edited: Feb 10, 2013
  15. crewchief888

    crewchief888 Senior Member

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    you can check the coupler without pulling the engine..
    my thought on the main coupler may be the splines are worn, the engine is turning, but the pump shaft is spinning at a slower speed.

    but it really sounds like the hyd pump coupler inside the pump broke or stripped it's splines. :(

    :drinkup
     
  16. crewchief888

    crewchief888 Senior Member

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    there should be a splined coupler between the hydrostat and gear pump, without seeing the parts breakdown, it may be show with the gear pump itself, or with the front hydrostat
    anything is possible with the relief,
    pull the main relief from the control valve, and see if the orings are blown.

    :drinkup
     
  17. jav

    jav Well-Known Member

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    First- Thanks for the help guys! It really makes me feel better to be able to bounce idea's off guys in the know.

    I mostly rebuilt this machine about 50 hours ago including having the engine out for rebuild. The coupler looked really good- no signs of spline wear and the universal joint had no play. It may have failed but I'm pretty good mechanically and the event didn't sound or feel like a what I'd expect if that coupler stripped or the U joint let go.

    BTW- how the heck do you check that coupler with the engine in?

    I've been studying the parts diagram and it shows a coupler between the rear (left) drive pump and the front (right) drive pump but it looks like the gear pump is driven directly off the rotating assembly of the front drive pump... I can't see a coupler and if it comes on either the gear pump or the front drive pump, it doesn't look like it can be purchased separately.

    I'm intrigued by this charge pressure possibility. My gear pump has 2 sections. Section 1 (front most) is the charge pressure side. Section 2 is what creates pressure for the valve block but it also looks like it feeds reservoir oil to the front drive pump (which is the left side drive). I'm going to re-read the oil flow explanation as this seems like this could explain why I have no lift and a week left side drive.
     
    Last edited: Feb 10, 2013
  18. crewchief888

    crewchief888 Senior Member

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    you can get to the coupler, however it's not easy,
    raise the cab, and lay on top of the pumps, reach around the side of the rear pump mount, inside the blower housing, and it's right there !! :D

    i dont have access to parts breakdowns right now, but from what i remember the hydrostat and gear pumps are splined together, most bobcats have a splined adapter coupler at the hyd pump end.
    i think i'd remove the hyd pump and take a look, something's gotta be broken

    :drinkup
     
  19. jav

    jav Well-Known Member

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    I can't open the cab in the garage so i'll be doing this outside in lovely New England winter weather. I'll probably order filters and a new relief valve tomorrow then wait for a decent day to pull the pump. I'm pretty sure I'm going to need to check the coupler between the drive pumps too.

    Any tips? I presume it can all come out from the front under the cab? Not really sure what to look for so I'm hoping the problem is reasonably obvious. With no drain on the oil tank- any tricks for not making a mess when the supply line comes off the gear pump?
     
  20. crewchief888

    crewchief888 Senior Member

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    pull the suction hose (from the tank to the pump) off at the pump,
    pull the open end up above the oil level in the tank, you'll loose some oil, but at least you wont have a huge puddle

    if i recall, and depending on the pump/control configuration, you'll probably have 2 or 3 hoses going in the top, or side of the pump, plus the hose clamped suction hose.

    2 bolts and the pump should slide right off.

    :drinkup