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ZF BW 255 No Oil Pressure

Discussion in 'Technical Discussion' started by DanSanLorenzo, Jun 20, 2016.

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  1. DanSanLorenzo, Jun 20, 2016
    #1
    DanSanLorenzo

    DanSanLorenzo New Member

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    Beaufort, NC
    I have a ZF BW 255 gear mated to a DD 16V92.
    I usually do not have oil pressure.
    But when I do, I'll guess once every 50 starts, I get good oil pressure and I can go in and out of gear until I shut the engine down.
    I was told that there could be trash in the control head or oil pump (pressure relief valve). I have removed and cleaned both and still have the problem.
    Anybody have any suggestions.
    This is on a 1987 80' San Lorenzo.
    Thanks,
    Dan
  2. Capt Ralph, Jun 20, 2016
    #2
    Capt Ralph

    Capt Ralph Senior Member

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    I'm confused;
    Every 50 starts you can shift the clutch and operate? Or every 50 starts the gauge comes up showing pressure,,, and you can operate then? Not the other 49 tries?

    I'm guessing the clutch works but the pressure gauge do not, but on the 50th try.
  3. DanSanLorenzo, Jun 20, 2016
    #3
    DanSanLorenzo

    DanSanLorenzo New Member

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    Thanks for your reply,
    Every one in fifty starts I have oil pressure. When I have oil pressure the gear works normally.
    These are analog pressure gauges which appear to be working.
    When the gauge indicates zero oil pressure the gear won't engage.
    When it does indicate oil pressure, about 180 psi the gear engages and I can shift forward, neutral and reverse, all day long until I shut down the engine.
    Any thoughts?
    Thanks,
    Dan
  4. Capt J, Jun 20, 2016
    #4
    Capt J

    Capt J Senior Member

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    Pull the entire screen/filter/scraper assembly out and clean it with brake fluid, and clean inside the entire housing it is in. Sounds like you have a paint chip or other blockage that floats and covers one of the passages. If not, I also had an oil pump go bad on one of these gears, but it would fluctuate a lot, but also made low oil pressure in gear 80-100 psi.
  5. Capt Ralph, Jun 21, 2016
    #5
    Capt Ralph

    Capt Ralph Senior Member

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    It does sound like a strange pump problem.
    Easy list checks;
    New problem? Any recent service?
    Filter checked (if equipped)?
    Are we sure the case is at the correct FULL oil level?


    Do you have trolling valves? all electronic?
  6. Capt Ralph, Jun 21, 2016
    #6
    Capt Ralph

    Capt Ralph Senior Member

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    A very quick peek in the users guide troubleshooting talks about a broken spring causing no pressure. I suspect in the valve manifold.
    I can see a broke spring causing a problem where some time it works.
  7. DanSanLorenzo, Jun 22, 2016
    #7
    DanSanLorenzo

    DanSanLorenzo New Member

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  8. DanSanLorenzo, Jun 22, 2016
    #8
    DanSanLorenzo

    DanSanLorenzo New Member

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    Thanks for your replies.
    I'm away now but will be back on the boat tomorrow.
    I will pull the filter and clean again, that makes sense if there is trash clogging an oil passage.
    The problem is recent.
    Oil level is good.
    Not sure about trolling valves ?
    All mechanical.
    Someone suggested that the pressure relief valve may be stuck in the open position.
    Does anyone know where this valve would be located? Supposedly there is a valve set to open and dump oil back into the sump if the pressure exceeds 300 psi
    I have removed and had cleaned the control head and oil pumps.
    Rcrapps, do you know where the valve manifold is located to see if there is a broken spring?
    Also someone suggested there may be a leak in the oil pickup preventing the pump from developing prime. Does this make sense?
    And, is it correct that if I crack the oil line coming from the pump I should have oil spewing out?
    Thanks again.
    Dan
  9. Capt J, Jun 22, 2016
    #9
    Capt J

    Capt J Senior Member

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    I wouldn't start cracking any lines, and I've never heard of a pickup breaking off or developing a hole in it on a gear. (It may be possible, but highly unlikely).

    If you pull the scraper assembly out, you're going to need a new $4 paper gasket for when you put it back in, I would do that and clean the cavity. Be very careful with the scraper assembly, they're about $2k. If this doesn't fix it, I would hire a trained ZF mechanic on it.
  10. Paul Nelson, Apr 26, 2017
    #10
    Paul Nelson

    Paul Nelson New Member

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    Also have the same setup & am out on charter at the moment although my problem is an elevation in G/box temp after approx. 2 hours of steaming.
    have removed screen unit & cleaned out screen.
    found some debri & refit scraper screen.
    raw water feed in & out is to desired temp.
    has anyone removed the attached raw water pump for a similar reason.
  11. 54bertram, Apr 27, 2017
    #11
    54bertram

    54bertram New Member

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    Location:
    port aransas tx.
    have same problem with mine is it the port or starboard tranny
    have done all the cleaning new impeller and changed oil (clean old oil)
    to solve temp elevation I actually go to full cruise for a few miles and the temp comes down to normal
    I wonder if its the extra gear for the counter rotating prop has something to do with it