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Troubleshooting - Hydraulic Pump vs. Hydraulic Motor - Scag Turf Tiger

Discussion in 'Mechanic and Repair' started by AlohaMowing, Sep 10, 2018.

  1. AlohaMowing

    AlohaMowing LawnSite Senior Member
    Messages: 373

    My Scag Turf Tiger, with 1300 hours on it, is suffering from a weak drive on the left side. This happens both in forward and reverse so it is not a simple matter of adjusting the control rod, although it does seem to be more of an issue in reverse than forward. The right side has good power, so I have to assume it is an issue with either the left hydraulic pump or left hydraulic drive motor. Before anyone suggests that this might be the dump valve not fully closed, I did check that.

    I first noticed this 2 or 3 months ago, and it has become worse over time. The amount of weakness seems inconsistent -- sometimes the wheel does not rotate, even on a level surface, other times, and at best, it is just moderately weak.

    A couple years ago I replaced the seals in the right hydraulic motor because there was a visible leak, but there is no sign of a leak currently. This troubleshooting goes beyond my mechanical expertise and I do not want to guess wrong on what part to replace. I have not found anything that would qualify as a true rebuild kit for the hydraulic pumps and motors, just seal kits, and the costs of the pump and drive motor are too much to guess wrong. If anyone can point me toward rebuild kits, or a source for a rebuilt pump and drive motor, I would be grateful.

    Thank you for all comments and suggestions.
  2. Walker56

    Walker56 LawnSite Fanatic
    Messages: 13,719

    When was the last time you replaced the oil/filter in the system?
    Go here with the serial number of your machine. Look up the part numbers for the pumps and wheel motors. Cross reference them on the net.
    Double check but from what I recall, TT use Hydro Gear pumps and Parker wheel motors. Here are the service manual for the pumps and motors. Use the troubeshooting guides to help you diagnose the issues you are having.
    If you decide to rebuild the pumps and or motors, here are some places that carry the parts required to effect a rebuild. Watch some YouTube videos as well as reading the manuals will assist greatly
  3. OP

    AlohaMowing LawnSite Senior Member
    Messages: 373

    Thanks for the info. I am still struggling with this.

    Both the pump and wheelmotor are Hydro Gear. The pump is model BDP-16A-410, the wheelmotor is model HGM-15E-3138. Looking at the manuals, it is possible to pressure test the pump. However, there seems to be no one on this island with the equipment to do the test.

    Beyond that, the manuals advise to disassemble, inspect each part, and replace internal parts as needed. That would be fine if one has a stock of the replacement parts, but the Turf Tiger is functioning at about 60% efficiency and I really can't take it out of service for the 2 - 3 weeks that it would be down if I did the disassembly, identified parts to replace, and had them shipped in. There seem to be no rebuild kits (beyond seal kits) with the parts most likely to be needed that might be ordered in advance.

    I thought about getting extensions for the hydraulic hoses to provide extra length so I might connect the right side pump to the left wheelmotor, and vice versa, which would be one way to determine whether the problem is in the pump or motor, but my local hydraulic shop would charge about $200 for the hoses and connectors -- a lot of money to spend on something that would be used only for this test.

    A new wheelmotor would cost about $500 and a new pump would cost about $600 -- either is a lot to spend unless reasonably certain it would fix the problem.

    There is a lot more that could go wrong in the pump that could cause what I am seeing, so it is tempting to play those odds and order in a new pump. Except, looking here and at other forums there are a lot of reports of this model of Hydro Gear wheelmotor failing, and for newer Turf Tigers Scag has switched to Parker wheelmotors. I did not run across discussions of failed pumps and Scag has stuck with Hydro Gear for the pumps for whatever that might suggest.

    Any more suggestions or ideas for identifying where this problem lies, or similar experiences and solutions, would be very appreciated.
  4. ricky86

    ricky86 LawnSite Silver Member
    Messages: 2,441

    Check the oil tank with an extendable magnet for metal.
    If so, the pump should come out for inspection.
    If only the thrust washer failed, repair might be possible.
    If the valve plate is gashed, that usually from the motor coming apart.
    If the motor is failing due to spline failure, it would still work.
    The motor is a HydroGear. Repair is usually futile.
    DXN1EL, hort101 and Walker56 like this.
  5. grobinsonpa

    grobinsonpa LawnSite Member
    Messages: 173

    Hi AlohaMowing, I just want to pass along my experience with the Hydro Gear 15 HGE wheel motors. I had an eXmark Lazer with the same wheel motors. At around 1200 hours both wheel motors started leaking at the output shafts and the right side was starting to get weak. I called eXmark tech support and they told me that the wheel motors needed to be replaced. He told me that Hydro Gear informed eXmark that the expected life of those wheel motors was 1500 hours. The tech also told me that it wasn't a good idea to rebuild the motors. ( Just like Ricky86 stated). I then spoke to a mechanic at the eXmark dealer I buy parts from. He told me that when he works on a mower with a bad Hydro Gear wheel motor, he just replaces it with a new Parker Wheel motor. They are cheaper to buy and they have a longer life span. Scag Turf Tigers just like eXmark Lazers used both the Hydro Gear and Parker wheel motors. Look up the parts breakdown for your year machine. I'll bet you will find both motors listed in the breakdowns. You will probably find that the Parkers were on the Turf Tigers with higher horsepower engines. Wheel motor replacement is pretty simple. They have 2 hydraulic lines attached to them. The motors attach to the mower frame with 4 bolts. The bolt mounting pattern on both brand wheel motors is the same. The only difficult part of the job is pulling the wheel hub off the old motor. I had to borrow a puller to do that. ... Like Ricky86 said, make sure you use a magnet and check for any metal in the hydro fluid tank. If you find some in there, you will need to flush all of that out. Otherwise, the metal will eventually destroy any new components you replace. Best of luck doing this job. Please feel free to PM me if you like, George
  6. OP

    AlohaMowing LawnSite Senior Member
    Messages: 373

    Thanks, George. You are right about Parker wheelmotors being used on the higher hp models, and I see that I can save about $50 with a Parker rather than the Hydro Gear. This sounds like the solution. And from what you were told by eXmark, it sounds like even if the original wheelmotor is not yet failed, it is very close to needing replacement anyway. I have previously replaced the seals in the right side wheelmotor so know that it will be quick and easy to replace.
    hort101 likes this.
  7. OP

    AlohaMowing LawnSite Senior Member
    Messages: 373

    Well, I ordered a new Parker wheelmotor from a favored parts source, but it turned out to be on back order with a 6 to 12 week delay, so I cancelled that order. Before placing an order with someone else it occured to me that there was another test I could do to confirm the problem was with the wheelmotor.

    To remove and install the wheelmotors on a Turf Tiger is not difficult nor terribly time-consuming, so I swapped the left and right wheelmotors, expecting that I now would see the weak propulsion on the right side. But, no, it still is the left side that is weak in forward or reverse.

    From this I conclude that the problem must be other than the wheelmotor, and probably in the pump. If anyone sees a flaw in this analysis or can suggest another place to check, please speak up.

    Otherwise I will be ordering a new pump. As near as I can tell, the only compatible pump is Hydro Gear BDP-16A-410, Scag part # 482695, although the parts diagram does show an alternative pump that has a fan built in (the addition of the fan reduces the cost of the pump by about $20, go figure).

    Thank you.
  8. ricky86

    ricky86 LawnSite Silver Member
    Messages: 2,441

    Did you check the oil tank?
    DXN1EL and Walker56 like this.
  9. ricky86

    ricky86 LawnSite Silver Member
    Messages: 2,441

    Because, if the pump is coming apart, you just pumped a crap load of debris into an otherwise good wheel motor.
    DXN1EL, Breezmeister and Walker56 like this.
  10. OP

    AlohaMowing LawnSite Senior Member
    Messages: 373

    It looks clean, and as a precaution I have drained and replaced the oil and put on a new filter, and will be doing that again whenever the new pump, or whatever else, goes on.

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