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lazer z wheel motor shaft broken

Discussion in 'eXmark' started by steve122, Jun 10, 2003.

  1. steve122

    steve122 LawnSite Member
    Messages: 208

    What causes wheel motor shafts to break? I just had one break (on a 27hp lazer Z) and it also took out the hydro pump. 2nd question, the dealer said if a hydro pump goes you don't roach the wheel motor, if wheel motor goes, it always gets the pump. Why would the hydro fluid be routed in such a way?
    Haven't got the bill on it yet, but am expecting $1500 for the pump, motor and labor. Dealer says the wheel motor shaft has a weak spot machined into it so it will break at a specified shock load. What is it protecting if, when it breaks, its going to roach a pump along with it? What part of machine is supposed to be protected by break point on shaft?
    This is the same machine that just had the pump on the other side of the machine replaced because a bearing went out in the pump.
  2. eXmark

    eXmark Manufacturer / Sponsor
    Messages: 4,258


    Causes are generally pressure, lots and lots of pressure. According to the wheel motor supplier extremely high pressure spikes can cause this type of failure.

    Fore the most part your dealer is correct. If a pump fails there is often a good chance that you can save the wheel motor. If the wheel motor fails it is rare that the pump can be saved.

    The flow is really the only feasible way to route the hydro system. The only way to really prevent the contamination from a failed part from moving to the next part in the line is to add a filter. This would mean adding a filter on each side of a pump or a wheel motor for a total of 4 per machine. The filters would also need to survive the same high-pressure spikes that caused the failure as well.

    I don't believe the link is designed to break. There is a noticeable narrowing of the shaft on one point but that necessary to mesh with the drive gears and not as a "weakened" portion.


  3. steve122

    steve122 LawnSite Member
    Messages: 208

    What will cause the type of pressure spikes that you are speaking of? The dealer keeps saying jumping curbs or bouncing over a hump in the grass and letting the wheel motor freewheel before it hits the ground again. What does the wheel motor manufacturer say?
  4. eXmark

    eXmark Manufacturer / Sponsor
    Messages: 4,258


    Your dealer is correct however there are often other factors on consider.

    Look at it as if you were pushing a cart. Each time you try to move the cart it is very difficult to get it moving. Once you've got it moving it's much easier to push. Now what happens if you try to stop the cart? The amount of effort increases unless you let it cost to a stop. What happens when you push the cart up against the curb? What happens the faster you try to perform these changes in movement? What happens if you’re stopped on a hill and try to start again? All of these things happen when you’re running a lawnmower. The big difference is they are happening more often, at higher speeds and at the same time.

    Keep in mind that when we are making all these changes in direction on the lawn the tires can slip and slid a little bit to help relieve the pressure. Put that same machine on the pavement and spin it around a few times at high speed you can easily see how the pressure spikes could increase.

    We’ve seen some operators exit curbs in the following manner. They gently ease the front casters off the curb and then jam the drive levers forward as the rear tires exit the curb. While the rear tires are in the air the can accelerate very rapidly. That is until the tires come bouncing down to the pavement. Does this always hurt the hydro drive system? No! Can it over time? Yes, it can.

    Take that same operator and watch him back slowly up to the curb and then pull back the drive levers as hard and as fast as he can. For a split second the mower does not move and then it leaps over the curb. During that split second the pressures in the hydro system can climb rapidly creating a pressure spike. The mower probably would have climbed the curb much easier if he/she had approached the curb at an angle and eased it up over the curb.

    When the machine is bouncing, such as when you exit a curb you can create pressure spikes. Combine that with the rapid acceleration when the tire is in the air followed by the tire grabbing again as the tire makes contact with the ground again you can seen increases in pressure spikes.

    The wheel motor manufacturer states that if the shaft/drive link breaks the only cause is pressure spikes. I’m not a hydraulic expert and can only assume that the wheel motor manufacturer knows what they are talking about. They’ve been doing this sort of thing for a long time and they have consistently been able to determine various causes for various types of failures.

    Another common cause for pressure spikes occurs during the transition between the trailer and the lawn. With the added traction created by the pavement the faster you change direction, stop, start etc. the greater the pressures with in the components. The Z’s are fun. They can be really fun on pavement. Even the operators aren’t getting carried away doing doughnuts, kitty’s, cookies etc. a little discretion can help. When you back the machine off the trailer and whip it around to head out to the property you can again create pressure spikes.

    One of the reasons we put the dampners in the hydro system is to smooth out the controls. Another reason is to reduce the speed you can move the drive levers. The faster you can move the levers the more strain you can put on the drive system.

    Most pressure spikes are caused by operators and how they react to the terrain rather than by terrain itself. Pressure spikes are always going to be there. The key is to make them as manageable as possible through design as well as operator input to the control.

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