Hydraulic problem

Discussion in 'Mechanic and Repair' started by Likestomow, Apr 15, 2006.

  1. Likestomow

    Likestomow LawnSite Senior Member
    Messages: 997

    Problem: at times, the hydraulic pumps will loose function. They won’t allow the motors to go forward or backward. The motors free-wheel.

    This situation first started when I changed the two hoses on the left pump. I ran the mower with the wheels suspended for 5 minutes and worked the levers. I drove it around a bit, up into the truck and all seemed to be well. I had a prior leak so I added hydraulic fluid. I didn’t know that this system used Mobil-1 15w-50.

    The next morning I tried to pull this mower out of the truck to change blades, but there was no function on the hydros. I could not move the mower forward or backward – there was nothing. I pushed the mower out, called the manufacturer and was told to change the fluid out with pure Mobil-1. I did that, taking the hoses loose and draining them along with the tank. I also took one of the wheel motors apart to see what was inside (curious). I put everything back, filled up with Mobil-1, purged the air, test drove and put on the truck.

    The next day I went to the first job and tried to move the mower when the same problem surfaced. The hydros didn’t want to respond. I played with the levers a bit and finally it creeped out of the wheel lock and I headed down the ramp. As I went down the ramp, I lost all hydro control and the mower free-wheeled straight down. I was parked in a driveway on a hill and was heading right for the road. Fortunately I was able to get the hydros to work right before I was going to abandon the ship.

    I am really puzzled as to why this is happening. The hydros work strong, just like usual, but the potential for “nothing” seems to be ever present. These are 10cc Hydro Gear pumps. Any suggestions would be welcomed.
  2. JHugh

    JHugh LawnSite Member
    Messages: 84

    It sounds like you still have some air in the system. Did you open the bypass valves on the pumps when purging the air? The way to do it is jack the rear up, open the bypass valves about 1 turn, run the engine full throttle, and stroke the sticks back and forth for at least 10 minutes or more. Make sure all of your fittings are tight. You did install a new hydraulic filter? Good luck.
  3. fixer67

    fixer67 LawnSite Silver Member
    Messages: 2,098

    Before let it down close the bypass valves and move the sticks back and forth for 5 to 10 minutes. Some manuals will tell you to open the by-pass valve and some say to close them when bleeding air from the system. So if in doubt then bleed it first with them open and then with them closed. Ferris says to do it with them closed and Grasshopper says open. Bob Cat says open for some models and closed for others. If possible always fill the new hydraulic filter before installing it on the machine. This helps to remove air from the system.
  4. Edgewater

    Edgewater LawnSite Senior Member
    Messages: 457

    At my dealer, on Dixie Choppers, they put an air hose on the hydro tank and pull the bypass valves right out. The blow air in until all of the air is out, and only oil is coming out of the valves. This is sure to get it all out. Any air in the pumps and they will be ruined.
  5. lawnmaniac883

    lawnmaniac883 LawnSite Silver Member
    Messages: 2,613

    I disagree, I do not believe air in the pumps will ruin them but will definately make them run poorly.

    Disclaimer- I am in no way a hydraulic expert.
  6. oldrustycars

    oldrustycars LawnSite Senior Member
    Messages: 301

    well.....the pumps are mechanically driven. the oil is used for hydraulic drive as well as lubrication. try running an engine for even 30 seconds with no oil and see if it damages the engine. at this point i'd be concerned about the amount of time the system has been run without oil going through it, if you put the motor back together correctly (just curious?) and if any damage has occured from using the wrong oil.
  7. lawnmaniac883

    lawnmaniac883 LawnSite Silver Member
    Messages: 2,613

    Well, it must have some oil in there if the motors will turn every so often. Sounds like an air bubble somewhere.

    There is no doubt that No oil will cause failure, but some air in the unit shouldnt be cause for complete failure. Not 100% on this one though.
  8. Likestomow

    Likestomow LawnSite Senior Member
    Messages: 997

    Thanks for the replies. Most of the machines we use have Hydro Gear pumps. They reccommend opening the by-pass valve to purge air from the pump. The pump does have a low volumn (gear) charge pump to fill the pumps, but I guess opening the by-pass valve helps hurry that process a bit.

    To purge the air from the pump/motor circuit, you have to just run the engine on a fast idle with the drive wheels off the ground for 10-15 minutes moving the levers after a while.

    At no point did I hear any cavitation, so I didn't fear a lack of oil. The pumps and motors seemed to work fine after I buttoned it up, at least enough to drive around a bit and up in the truck. It was after it had sat over night that the problem surfaced. It was as though all the oil leaked out of the motors, although I know this can't happen.

    I am going to call Hydro Gear on Monday if I get time and pick their brain. There has to be an answer to this phenomena.
  9. Restrorob

    Restrorob LawnSite Fanatic
    Messages: 11,029

    If Dixie Chopper heard of them doing this they would Probably pull their dealership contract. :dizzy: There is less chance of blowing internal pump seals and O-rings bleeding as Dixie suggest which takes less time and makes less mess.

    A return oil line could be sucking air while running and not leak oil when not running, Check all your return hose fittings. I have seen this a few times.

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