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  1. #1

    Allison M15 won't go forward, part II

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    bobk
    Senior Member Posts: 1,172
    Join Date: Aug 2005

    Allison M15 won't go forward - 11-09-2010, 11:45 AM
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    Hi Guys, we are about 80 miles from home after almost 1000 miles, fueled in Canaveral and lost the foward gear on the starboard engine when we undocked. Reverse works fine and the gear oil pressure is normal. The shifter seems to be moving the shift lever properly and the shaft is also rotating as it is shifted. Oil level is proper. The prop seems to be turning slowly when the engine is revved up in foward. Any thoughts? Mechanic recommendations in the area if this is serious?

    Bob Kassal
    Chateau de Mer
    1981 48MY
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    HERE IS AN UPDATE: Figured I'd start again since the other post morphed into single screw handling.

    The on scene Cummins mech (Dennis) tried raising oil pressure as it was a little low. The pressure drops down when engaged, and doesn't rise significantly when left in gear.

    He also cleaned the screen, but found just a few bits of debris. No blockage. The prop turns normally in reverse, but much slower in forward. The oil is clear and has no odor.

    When cold the next day the forward gear engaged normally, but once again was kaput when it warmed up. The DD mech (Ken) noted the oil was frothy with air, and eventually suspected the oil pump might be at fault. It has been pulled and is being checked at a repair facitity. I believe they consulted with Allison before doing this. They are checking out the simple things before tearing into the transmission.

    Bob Kassal
    Back in Port St. Lucie with the boat in Canaveral

  2. #2

    Re: Allison M15 won't go forward, part II

    Bob, thanks for the update and putting this thread back on track. Did you add oil to the gear recently? too much oil in an Allison will result in aerated oil when warm. I had a similar problem with one of mine after it was rebuilt. Mine ran fine other than the oil being a bit whipped up. A leak on the suction side can do the same. Keep us posted and good luck.
    Jack Sardina

  3. #3

    Re: Allison M15 won't go forward, part II

    Thanks for the update. It's good to hear you have good mechanics taking a logical approach to the situation rather than just jumping in and tearing things apart. Good luck and keep us poated.

  4. #4

    Re: Allison M15 won't go forward, part II

    Quote Originally Posted by saltshaker View Post
    Bob, thanks for the update and putting this thread back on track. Did you add oil to the gear recently? too much oil in an Allison will result in aerated oil when warm. I had a similar problem with one of mine after it was rebuilt. Mine ran fine other than the oil being a bit whipped up. A leak on the suction side can do the same. Keep us posted and good luck.

    The tranny was a bit low when the issue began. I added oil to bring it a bit ablove full, but no joy. By the way, the rear main on the other side leaks and I allow it to get two quarts high before removing some, and that extra two quarts hasn't led to air entrapment (yet?).

    Bob Kassal

  5. #5

    Re: Allison M15 won't go forward, part II

    Hey Bob... now that the dust has settled, lets look at a few facts. I dont think anyone has gone near the removal issue in earnest, so lets back up a bit. ..
    On my 58 with 12-71s, the hatch would be barely big enough to lift the bare block straight up. No way would the gear come out without cutting a hatch in the floor for it. Taking a wild guess, whats in yours for power? If they are 6-71s, there a good possibility that you can slide the engine forward enough to be able to raise the gear after unbolting it. The hatch job was a considerable struggle on mine and wouldnt wish that on anyone!
    If and when its apart, you may want to replace the stuffing box hose, and repack and address the coupling trueness for ease of alignment upon re-assembly. I would also install a new rear main seal since the flywheel will go with the gear to replace the clutch pack O ring inside. DD also recommends new flywheel bolts with each removal.
    I understand you have a nice boat and prefer to keep it that way. I am not trying to spend your money, but these are issues one is faced with when having the work done. I did this ALL myself two years ago along with props and cutless bearings, so I have a fair grasp of the scope of this job.
    A lot of my job was remediating bubbas attempt to make repairs in place, which neccessitated using hammers, screwdrivers and pipe wrenches. Feel free to PM me with honest questions resulting in honest answers without all the bantering in between.
    So on that note, make sure the china is all packed away and the silverware is taken home so it dont end up in the local pawn shop! LOL... ws
    yachtsmanWILLY

    I used to think I knew everything until I found the experts HERE; Now I know I dont know SQUAT



    www.flybridge.proboards.com
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  6. #6

    Re: Allison M15 won't go forward, part II

    Thanks for your suggestions. I always try to catch the auxiallary stuff like the rear seal if a tear down has to be done. On my trawler, I found water from a cooler leak in the transmission at the end of a cruise and insisted the entire unit be removed and all available parts replaced since they had to be in there anyway. I'm sure Scott will pass along the tip about replacing the tranny bolts/hoses etc..

    Pulling this tranny will not be as bad as your job if it gets to that. The engines are 6V92TA's but the boat was designed for 671N's so there is longitudinal space to work. One of the same boats that I looked at before buying this one had the rear main seal replaced and I knew the mech who did that job. No new holes etc. Just $$$.

    Bob Kassal
    Living on dirt at Tarpon Bay Yacht Club, PSL

  7. #7

    Re: Allison M15 won't go forward, part II

    Hi Bob,

    I live in North Tampa,not to far from you in Tarpon. Currently I am working in Jamaic, but expect to be in town Tuesday, if you are still there, I'll swing by and take you to dinner, or give you a ride if you need to get around. Lets me know.
    Last edited by Boatnut; 11-13-2010 at 11:47 AM.

  8. #8

    Re: Allison M15 won't go forward, part II

    I think it is Port St Lucie.

  9. #9

    Re: Allison M15 won't go forward, part II

    Thanks Dave, I was thinking Tarpon Springs duhhhh!

  10. #10

    Re: Allison M15 won't go forward, part II

    Quote Originally Posted by Boatnut View Post
    Hi Bob,

    I live in North Tampa,not to far from you in Tarpon. Currently I am working in Jamaic, but expect to be in town Tuesday, if you are still there, I'll swing by and take you to dinner, or give you a ride if you need to get around. Lets me know.

    Hi Boatnut,

    Yes, I'm at Tarpon Bay Yacht Club in Port St. Lucie. It's a small condo complex with docks for up to 50' boats.. a couple can exceed that. Best deal in Florida.... But I digress, many thanks for your thought and your offer.

    Bob

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