Allison Question

Discussion in 'General RVing' started by hwjohnson47, Mar 23, 2012.

  1. hwjohnson47

    hwjohnson47 Junior Member

    I have a 2007 Workhorse Chassis with an Allison tranny. Recently I got a tranny warning light and an "Auto Park Failure" message. Are the two related and how do I check this out before taking to is about 50 miles away. Tranny performs fine and has no leaks or overheating problem.
  2. LEN

    LEN Senior Member

    We are looking, but I have no experience on this one.

  3. H2H1

    H2H1 Senior Member

    Please post back your finding. I also have a Workhorse Chassis and a Allison tranny, so for no problem but like to know what your is and the fix just in case I should have it to come up.
  4. dbarton291

    dbarton291 Senior Member

    Which transmission is it? Does the transmission have a parking pawl in it, or does the vehicle have its own parking brake system?
  5. LEN

    LEN Senior Member

    Here is info I found on it.


    The J72 system incorporates a unique full-circle parking brake. The automatic
    electric/hydraulic parking system controls the transmission/propeller shaft mounted parking
    brake. This system consists of a pump motor relay, vehicle ignition relay, electric/hydraulic
    pump, reservoir, proportional relief solenoid valve, pressure transducer, and an electronic
    control module (ECM). The ECM monitors seven inputs from the vehicle and controls the
    pump motor relay, auto-park light, park brake warning light, buzzer, proportional valve, and
    pressure transducer.

    To release the parking brake, push in the park brake switch pull-button and move the shift
    lever on the steering column from the park position or select "D", "N" or "R" on the push
    button shift control (optional AllisonTM transmission control). Note both situations must
    occur for the brake to release. Once the ECM receives the signals from the transmission and
    button contacts, the ECM closes the solenoid valve and closes the pump/motor relay allowing
    current to flow to the motor. The pump/motor then supplies fluid to the brake assembly. The
    brake assembly includes a friction disc clamped by a piston through force of an internal
    spring. The fluid pressure acts on the piston overcoming the spring tension that clamps the
    friction disc, releasing the brake. The pump motor will shut off when the transducer reads the
    fluid pressure of approximately 1400 psi. The solenoid valve holds pressure in the system while
    the brake is in a released state. The ECM monitors system pressure from the pressure
    transducer and energizes the pump motor when system pressure drops below approximately
    1200 psi.

    Putting the shift lever back to park, selecting "P" on the push button shift control, turning off
    the ignition, or pulling the push/pull switch prompts the ECM to de-energize the solenoid
    valve dumping fluid back into the reservoir. As the pressure decreases, the spring force clamps
    the piston back against the friction disc and applies the park brake.

    The "AUTO PARK" WARNING LAMP turns on when the system pressure is less than 900 psi
    and the ECM receives the signal from the transmission.

    The PARKING BRAKE WARNING LAMP turns on when system is below 900 PSI and when
    the parking brake pull-button is pulled out.

    The PARK BRAKE PULL SWITCH is mounted on the instrument panel. This is a manual
    activation switch for the park brake. This switch is normally closed, pushed in. The body
    manufacturer determines final location of this switch.

    The PARK BRAKE PUMP MOTOR RELAY is located above the fuse box on the front
    driver's side of the radiator core support. It receives ground from the ECM and acts as the
    automatic control circuit for the high voltage current required to run the pump motor. When
    the ECM supplies ground to the relay switch, the contacts close to complete the feed circuit to
    the pump motor.

    The IGNITION RELAY is located next to the park brake pump motor relay on the front
    driver's side of the radiator core support. It monitors the vehicle's ignition switch to turn
    on/off the supply of the fifteen and forty-five amp fused-lines that the ECM and electric
    motor use. If the relay was not present, the ECM would be continually powered since it would
    be directly connected to the batteries.

    This unit mounts on the driver's side of the radiator core support and is self-contained/environmentally

    The AUTO/ELECTRIC/HYDRAULIC ACTUATOR controls the pressure in the park brake system to
    either set or release the park brake. The actuator consists of a mounting bracket and the
    following components:

    The ELECTRONIC CONTROL MODULE or ECM is an analog logic device that monitors the various
    vehicle conditions then controls the actuator accordingly. It is the "black box" mounted underneath
    the actuator mounting bracket. It connects to the vehicle via a fourteen pin connector, to the
    proportional solenoid valve via a two pin connector, and a pressure transducer via a three pin
    connector. The ECM is powered by two different sources. First, it receives power primarily through
    a fifteen amp fuse. Secondly, the ECM receives power off of the forty-five amp fused-line that the
    pump motor relay also uses. Below is a detail of the pin connections of the ECM as well as the
    solenoid valve and pressure transducer.

    The PUMP/MOTOR ASSEMBLY consists of an electric motor, geared pump, aluminum port
    block, and a semi-transparent fluid reservoir. The port block holds the proportional solenoid
    valve and pressure transducer. The pump provides fluid pressure for the system. A pressure
    relief valve in the port block limits system pressure to around 1700 psi.

    The PROPORTIONAL SOLENOID VALVE controls when fluid can return to the pump
    reservoir. When the parking brake is released, the valve is closed to hold pressure in the
    system. When the parking brake is applied, the valve opens to allow fluid to return to the
    pump reservoir. If the vehicle is at a speed greater than five miles per hour (5mph) and the
    pull button is pulled, the valve will remain open for a few moments and then release the
    pressure slowly for a gradual apply of the brake. NOTE: The park brake is NOT designed for
    dynamic stops; if a dynamic stop occurs see the nearest service center for brake inspection.
    The PRESSURE TRANSDUCER monitors the pressure of the system and relays that
    information back to the ECM. The critical pressure values are the cut-in and out for the
    motor which are 1200 psi and 1400 psi, respectively.

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