[lro] ZF transmission (no Series content)

From: C. Marin Faure (faurecm@earthlink.net)
Date: Wed Dec 18 2002 - 02:05:16 EST

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    Recently some of you commented on the possibility of the ZF automatic
    transmission as fitted to the Range Rover having problems if the engine is
    revved up in neutral or park after the transmission has been in gear.
    Apparently fluid can fail to drain from the clutch packs when the
    transmission is shifted into neutral, so that when the engine is revved
    with the brake on, damage can occur to the clutch packs.

    Comments were made about emission testing, which requires the engine to be
    revved in neutral or park with the brake set, and the potential for
    damaging a faulty ZF transmission by doing so. Some of you said you insist
    that your Range Rover's engine be turned off and the transmission allowed
    to sit for at least a minute to let the fluid drain off, after which the
    engine can be started and revved up for the emissions test.

    Not knowing squat about the innards of an automatic transmission, I wonder
    if rather than turn off the engine for a minute or so, simply revving the
    engine a bit after shifting the transmission into neutral with the brake
    OFF would immediately indicate if there was a potential problem with the
    fluid drain? After all, if the fluid has failed to drain properly and is
    still in the clutch packs, reving the engine in neutral would cause the
    vehicle to move, would it not? If it did move, then the procedure of shut
    down, wait, and re-start would be the course to follow. If it didn't move
    when the engine was revved in neutral, couldn't one assume the drain-down
    function was working properly, and it was safe to rev the engine for the
    test?

    Like I said, I know nothing about automatic transmissions except how to
    shift them, so perhaps my logic is full of holes. In this state (WA), you
    operate your vehicle yourself for the emissions test, so it would be a
    simple enough thing to do the neutral/brake off/rev-the-engine-to
    see-if-the-vehicle-moves test. In states where you have to turn your
    vehicle over to a tester to run through the process, it might be easier to
    simply have them shut it down, wait, and restart rather than try to explain
    some other process.

    The earlier thread was the first I'd ever heard of the potential for a
    drain-down problem in the ZF transmission (or any automatic transmission
    for that matter). I'd be curious to know how common this failure really is.

    ________________________
    C. Marin Faure
      (original owner)
      1973 Land Rover Series III-88
      1991 Range Rover Vogue SE
       Seattle, WA
       marin.faure@boeing.com
       faurecm@earthlink.net
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