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ZF Transmission with fluctuating pressure?

Discussion in 'Engines' started by Prospective, Sep 2, 2020.

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  1. Prospective

    Prospective Senior Member

    Joined:
    Sep 27, 2016
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    Location:
    New England
    Would welcome any thoughts on this.... Have a call in to my mechanic to advise as well but wondering if this should cost me my last summer cruise this weekend.

    Boat is a Yr 2000 43' Ocean SS. Engines are 480 Volvo Tamd74 EDC. Transmissions are ZF280 A-2.

    Symptoms....

    After the past 2, maybe 3 trips, returning home after longish runs on plan (2-3hrs) I typically go to the fuel dock to pump out then head to my slip. In past couple of trips, noticed what I thought was a slight bit of roughness as I put starboard transmission in and out of gear while maneuvering to dock at idle speed. Was/is so subtle and doesn't seem to happen at start of trips that I chalked it up to my imagination or current running (which is strong in my marina). However, on last docking I also noticed my starboard transmission oil pressure fluctuating. Needle didn't go way down but bounced around at or near full pressure. Typically when in gear, pressure would peg at full and not move. No other issues and gears functioned normally.

    Plan is to drain oil and check oil and filter screen for any visible metals. May also swap gauges as that's easy. Swapping sensors may be more difficult. If I find something in oil then I know I've got a real problem. But not sure what to do if oil looks good. Also note that 2 years ago I had both transmission couplers replaced.

    Anyone want to throw out some advice, guesses, or wild internet speculation on what the possible problems are or what to do next?
  2. Capt J

    Capt J Senior Member

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    Pull filter screen out, wipe out cavity and clean screen with brake cleaner. If that doesn't solve it, the ZF oil pump is going bad and will need to be replaced. They're expensive.
  3. Capt Ralph

    Capt Ralph Senior Member

    Joined:
    Sep 8, 2004
    Messages:
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    Location:
    Satsuma, FL
    Your on the correct path.
    Fill us in on your results. Get a test pressure gauge on the pressure pimp if you or your tech can.

    Also, how is your engine idle? stumbling? low? Solid rpm is kept when the clutch is engaged?

    ZF oil spec from their manual;
    ZF 220 to ZF 83700 with all derived variants
    A, V, IV, C, U, D, NR, NR2, NR2H, NR2B, TS, ATS, VTS, IVTS
    Lubricant class 04A
    Engine oil according to the specification / requirement:
    - API CD/CE/CF-4/CF/CG-4/CH-4/CI-4/CI-4 Plus/CJ-4/CK-4
    and / or API SF/SG/SH/SJ/SL/SM/SN
    and / or ACEA categories A/B/E
    - Viscosity grade: SAE 30 (also SAE 40 in hot-weather countries or at oil sump temperatures over +80°C)
    - Base oil API Group 1 / 2 / 3 / 4
    Note:
    1. All trade products which satisfy the above specifications may be used. There will be no product listing.
    2. For transmissions which are classified according to DNV, fluids of the class 04A may not be used. Instead of
    this fluids according to classes 04B or 04C may be used.

    There more more notes, Just stay with a reliable straight weight oil.
  4. Beau

    Beau Senior Member

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    Beaufort, NC
    Also, probably not the problem, but check the tranny wire leading to the sensor. The gauge can peg if there is a break, momentarily or otherwise, in the connectivity.
  5. Capt Ralph

    Capt Ralph Senior Member

    Joined:
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    10,610
    Location:
    Satsuma, FL
    While your there, Change the oil in the other clutch and send the two samples in to a lab.
  6. Prospective

    Prospective Senior Member

    Joined:
    Sep 27, 2016
    Messages:
    222
    Location:
    New England
    Just wanted to update and say thanks for the suggestions. Changed the oil and cleaned the filter last week. Filter maybe had one or two super fine very small metal shavings in it. Oil was somewhat dirty and I honestly can't recall when it was last changed (my bad). Drained oil from bottom of transmission. Could find no particles in it by feel. Even dragged a magnet thru it and nothing there. Didn't think about oil samples until I'd already disposed of the oil but that might have been a good idea.

    Test drove after oil change and used the boat all weekend. Needle still dances a bit. It dances a bit while in gear but never drops below 300psi. When I drop to neutral it drops down but stays steady. When under weigh above idle they both pin at max and don't move (not shown).

    At this point I don't think there's much left to do. Honestly I could not detect anything particularly unusual about how the transmission operates. I really think any roughness I thought I felt may have been in my imagination and the transmissions worked well all weekend. I can't even swear that the needle didn't do this before and I just never paid much attention.

    At any rate, I had another mechanical issue over the weekend that's now got my attention. I'll share that one in a new thread. Thanks for all of the help.
  7. Capt Ralph

    Capt Ralph Senior Member

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    Are you over filled on oil? Some foaming of the oil could cause a bouncing needle.
    Small ZF clutches are checked warm, engine off for a minute. NEVER over filled.