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Bing Bang! Twin Disc Transmission?

Discussion in 'Engines' started by RichV, Apr 15, 2024.

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  1. RichV, Apr 15, 2024
    #1
    RichV

    RichV Member

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    Oct 26, 2020
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    Location:
    Massachusetts
    Details:
    (2) DD-507-2 1.97:1 Twin Disc Transmission
    (2) DD 6-71 TI
    1990 Ocean Yachts 48MY
    3/30/2024 Left St Augustine heading north on ICW, approaching the Frances & Mary Usina Bridge with the current, I get a call on the radio from a tug "Sorry captain, you're gonna have to wait for us" He was towing a 1/4 plus mile pipe with 2 other tugs on the side and one on the end. 15 minutes later we get through the bridge. In hindsight I would have turned the bow into the current, but at the time I didn't think it would take 15 minutes.

    BANG
    See attached track. We had only ran about 30 minutes at the most from St Augustine, pretty much all at idle because of traffic, so the engine and trans were not too warm. The tug and tow was on our port, with 17' of water on our starboard. On the 2nd reverse track I hear a bang and assume I hit something.

    10 minutes later I hear an even louder BANG. We get through the bridge and I check below; I see a little water from the starboard dripless that I never have seen before, plus a wobble in the shaft that was never there before. We proceed north to Palm Cove Marina (Jacksonville Beach) mostly at 1000 - 750 rpm.

    On the way I called a diver to meet us in Jacksonville Beach. There he reports no damage to the props and the shafts turn easy and assumes their straight.

    Transmission?
    So I investigate the transmissions; starboard is low 3 quarts. I fill and do a sea trial; no issues.

    At this point I can't be sure of anything. But, I recently started using an Actisense W2k-1 (they have a newer version now). It records all network data to a SD card, 1-2 times per second in a spreadsheet with a graph. I downloaded the file and looked at the transmission oil pressure. See attached.

    A short drop in pressure could easily be an electrical connection issue, BUT, when I compared it to a cruising speed file, there are no drops in psi. At the bridge the transmission had momentary drops in psi:

    Stbd-74 psi
    Stbd-18 4psi
    Stbd-71 psi
    Port-86 psi
    PSI per label is 280 but the typical PSI running is; 270 port & 235 stbd.
    Next step; change oil & clean oil screen.

    Would a big drop in oil pressure like this make it come out of gear or bang?

    Attached Files:

  2. Capt Ralph, Apr 15, 2024
    #2
    Capt Ralph

    Capt Ralph Senior Member

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    The TD 507 / DDC 6-71 combination must be near one of the most bomb proof packages assembled.
    You may have the tall HP 6-71 TIBs and that clutch can take it with no issues.
    Idling around should not be an issue. Even in reverse gear for long amounts of time. Both clutch packs are the same for r/f.

    Tell us about your clutch controls, all cable or some electrical option.
    Hopefully not original Mathers.

    Oh, during the bang, did the engines stall?
  3. RichV, Apr 15, 2024
    #3
    RichV

    RichV Member

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    Location:
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    They did not stall.
    Hynautics controls. Had trouble getting the port into reverse last year, until I bled it correctly, and have had no issues since.
  4. DOCKMASTER, Apr 15, 2024
    #4
    DOCKMASTER

    DOCKMASTER Senior Member

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    Location:
    Ketchikan, Alaska
    When you are saying oil pressure I presume you are referring to clutch pressure? Yes, a drop in clutch pressure of sufficient amount can reduce the clutch pressure to a point where the clutches slip. Most marine gears will start to have clutch slip around 35 psi or less. However, this wouldn’t explain the bang you heard, shaft wobble and shaft seal leakage. BTW - this is exactly what trolling valves do. They reduce clutch pressure to the point where the clutches slip. As long as you stay under 1,000 rpm there is no issue.
  5. Capt Ralph, Apr 15, 2024
    #5
    Capt Ralph

    Capt Ralph Senior Member

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    You typed you saw a shaft wobble and now all is good?

    Reads like an old drive saver folded on itself.
    Do you have drive savers or plastic/rubber packed shaft couplers?

    Another idea,
    I wonder if the shaft backed out of the coupler a bit. Mad a bang when it found center and went back in place.

    You do not have a clutch issue.
    But if there is still a shaft wobble, you will have a oil leak soon.

    I've had bangs running over hawser and crab pots also.
  6. RichV, Apr 16, 2024
    #6
    RichV

    RichV Member

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    Location:
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    Someone else told me if there was a problem with the transmission, I would know it. Meaning, it's either fine or it wouldn't work.

    I still have a slight wobble, and I have the plastic drive savers.

    I won't be back onboard for a month. I will check to see if the shaft is backing out.
  7. Capt Ralph, Apr 16, 2024
    #7
    Capt Ralph

    Capt Ralph Senior Member

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    There is your problem.
    I can not get into the science but trust me, There is your problem.
    The last set I worked on also had a loose motor mount.
    Failures became complete while operating in reverse.

    Your bang; spinning and locking against the safety (get-home) stud or strap.
    Last edited: Apr 16, 2024