Allison Transmission w/ Pacbrake that won't engage

Discussion in 'Class A / Diesel Pushers' started by llobbe7, Aug 19, 2008.

  1. llobbe7

    llobbe7 New Member

    Please help Allisonman...I have a 95 Beaver Patriot with Cummins 8.3 and Allison MD3060 and I am having trouble with the exhaust brake. The switch on the dash lights when selected, and the transmission downshifts to 4th, but no retarder action. Just previously I had an Allison certified shop in the Battle Ground Area install a new TPS (cable was broken) and recalibrate the system but the problem persists. With the switch in the retard position if I disconnect the control wire at the exhaust brake relay and ground the terminal the retarder actuates. Where does the control wire get its ground? What do you suggest I try next? Oh BTW, the cruis control is also inop, the light on the switch does not come on when cruise is selected, are these problems related maybe a speed sensor on the trans?

    PS- A fellow pusher operator recommended you to me- was perfectly impressed with your operation.
     
  2. dbarton291

    dbarton291 Senior Member

    Re: Allison Transmission w/ Pacbrake that won't engage

    The way most of them work is the trans ECU provides the ground for the pac brake circuit when it sees the pac brake switch on, and the operator off the throttle. Allisonman is really good, and may have a different approach, but I would suggest tracing the ground wire from the exhaust brake relay and see where it goes. It may be a broken wire, or an improper connection, or possible the trans ECU is no longer providing that ground. Good investments to help do this properly, would be a wiring schematic on the coach, and the proper Allison Troubleshooting manual for the transmission control system you have. (WTEC, WTEC II, etc.).

    If you had access to Allison DOC (troubleshooting software), you could check and see if the trans ECU is recognizing retarder request coming on, and then activating the retarder enable circuit.

    If you had a trans speed sensor problem, you should have an active trouble code and other problems.

    The cruise problem may be completely separate from the transmission. In many coaches, the only interface the trans has with the cruise control is providing an output speed signal. The trans doesn't normally control whether or not the cruise comes on.

    Just my 2 cents.
     
  3. astropaul

    astropaul New Member

    RE: Allison Transmission w/ Pacbrake that won't engage

    Hi,
    Just "thinking out loud" here... my Beaver has a similar setup in terms of the transmission... do you have an onboard computer that can run a diagnostic? I have one on the dash that was factory installed; playing around with the buttons (what, read a manual??!) I discovered that you can run a diagnostic routine. I don't know how good it is, but it might pop something up for you assuming your model has the computer.
    Astropaul

     
  4. llobbe7

    llobbe7 New Member

    Re: Allison Transmission w/ Pacbrake that won't engage

    Thanks dbarton291 and astropaul for all your input. Allisonman's shop faxed me a copy of the wiring diagram for the WTECII and a copy of the troubleshooting section. It looks like the problem is either a bad connection or wire between the ECU and the VIM, a bad VIM or Bad connection/ wire between VIM and ex brake relay.

    astorpaul- Did you get your wiring problem with shore power figured out?
     
  5. dbarton291

    dbarton291 Senior Member

    Re: Allison Transmission w/ Pacbrake that won't engage

    Allisonman once again comes through! What a superman. I'm glad his cape didn't get caught in the fax machine again. He hates that when it happens.
     
  6. astropaul

    astropaul New Member

    Re: Allison Transmission w/ Pacbrake that won't engage

    Haven't found the issue yet, but I have been learning the system... found my transfer switch and I have a Glendenning CM-7 direct-connect power reel. I've done a quick inspect on my power cord and it "looks" ok and "feels" ok. Hoping to get to it this weekend and take a meter to some of this stuff.
    Thanks for asking llobbe7! As soon as I figure out what it is (I'm saying when, not if :) ), I'll post back on the thread I started. Hope you find that bad connection!
    Astropaul

     

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