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  1. #1

    Join Date
    Oct 2011
    Posts
    3
    Location
    Ohio
    Mower
    Scag

    Scag STT61 hydo pump failure

    The seal for the left hydro pump blew on my 2001 Scag STT61. Replaced the seal but the left side would not operate. Pulled and disassembled the hydro pump and found the rotating members had rubbed and created quite a few metal shavings. Three of the pistons in the rotating cylinder would not even move due to the buildup of metal shavings in the springs. I have purchased a new BDP-10L-121 hydro pump and have a few questions before replacing. What precautions should I take prior to replacing the pump. I know I need to flush the system but how should I go about flushing the system with the pump removed. I have seen comments abouts replacing the wheel drive motor at the same time but I don't want to spend another $400 if I don't have to. Is there a way to test the wheel motor? Should I remove the wheel motor to flush? Have not seen a parts breakdown so I am not sure how/if to disassemble. Any help would be appreciated.

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  3. #2

    Join Date
    May 2010
    Posts
    5,446
    Location
    Kansas, Butler county, Just east of DooDah
    Mower
    CTL

    Re: Scag STT61 hydo pump failure

    Hello and WELCOME to LMF...

    The wheel motor is Much more robustly built than the pump... But for sure if you have been pumping metal parts around there will be pieces in the wheel motor, motor relief valve... You should be able to determine if anything is compromised in the WM by rotating it...
    If the filter is on the suction side of the pump,You can flush out the oil reservoir, clean up the bottom of it...
    If the filter is on the end of the return line there will be nothing in the tank.
    If you want,The hoses and WM can be flushed out using fresh oil from the tank, run the WM one direction with only one hose hooked up... and discharge from the Motor into a 5 gallon pail... then hook the other port to the other side of the pump and run the WM in the opposite direction... with the discharge again running into the pail... You can re use this oil because all the contaminants will sink to the bottom...

    There is no need to get too obsessed with flushing, the WM is much more forgiving than the pump... I have seen Many pumps swapped with no flushing at all...just swap and go... The inlet line to the pump is the one you want to have very clean... KennyV

  4. #3

    Join Date
    Oct 2011
    Posts
    3
    Location
    Ohio
    Mower
    Scag

    Re: Scag STT61 hydo pump failure

    Thanks for the info Kenny. I was hoping that was the case but I didn't want to mess up the new pump if the WM was also bad. I have the rear jacked up and the wheels off and the WM turns free with the hydro pump removed. The other wheel turns with much more resistance probably due to the hydro pump still installed. Is the pump suction fitting located between the WM fittings on the pump? If so, it is coming directly from the filter. Your help is greatly appreciated. Moose

  5. #4

    Join Date
    May 2010
    Posts
    5,446
    Location
    Kansas, Butler county, Just east of DooDah
    Mower
    CTL

    Re: Scag STT61 hydo pump failure

    I'm not sure where Scag set the filter on your set up.. It can either be on the return line to the reservoir OR on the suction side of the pump...
    The wheel motor 'discharge should go to a common reservoir before it gets back to the pump...
    Should be very easy to follow the hydraulic lines to find what layout you have...

    Turning the wheel motors will cause them to act like a pump... you have to have some place for the oil coming out of the WM to go ... That is why the disconnected set turns free. That is also why the system can be damaged if it is towed... KennyV

  6. #5

    Join Date
    Oct 2011
    Posts
    3
    Location
    Ohio
    Mower
    Scag

    Re: Scag STT61 hydo pump failure

    Finally got back to working on the Scag. Since I'm retired this is a spare time project. Replaced the bad hydro pump and replaced and flushed the fluid in the reservoir. Tried to flush the WM but could not get it to act like a pump so could not get fluid through it. Hooked up the hoses and gave it a try to see if I could get it to drive but no go. Figured I now had the system pressurized so I jacked it up and tried to turn the wheel and WM. It was freewheeling whereas the good side WM was hard to turn. Seemed to be a occasional catch or freeze when turning the bad side so I decided to pull the WM and check it out. What a bear to pull. Openned up the WM 7 bolts, scribbed the plates and started to unstack. Got to the Drive Link, I think they also call it the dogbone and it was sheared off. Tried running the pump discharge into a bucket with WM removed to see if there was pressure. Got flow when starting motor and got pressure in both directions when using the stick. Oil was milky but figured there was probably air in the system. Trying to decide whether to find a new dogbone or one from a used WM or buy a new WM. Now am wondering to to proceed. Due to the metal pieces and grit in the WM and the WM having 2500 hours on it, I think I will buy a new one. Now am hoping I did not mess up the new hydro pump. Should I pull the pump and inspect or go ahead and try with a new WM and hope the filter got the shavings. If the pump has been compromised it can't get any worse but will I get metal into the new WM. Not sure if the filter is on the suction or discharge of the pump. Is the suction line on the side of the pump (this is the one going to the reservoir) or between the discharge lines to the WM (this line goes to the filter). Can't tell the flow direction by looking a the pump.
    Any help will be greatly appreciated. This was a project for a retiree but has turned into an expensive proposition. Not sure what I could get for it if I tried to sell it in this condition but may be a consideration. With a new WM I will have $800 into it and a possibility of another bad hydro pump.

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