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  1. #1

    Allison Gear Box Problem

    Hi All,
    Some advice please.
    When I was returning from a long fishing trip, I noticed that the port engine revs kept dropping. Checked the port engine throttle/gear control & it had come right out of its bracket. The bracket was badly made and weak. Also now the port engine would not go into forward gear unless I revved up a lot & the transmission oil alarm came on. Checked oil in transmission & it was full, plus new, I had changed oil (40W) recently.
    Got home slow & careful. Had new cable & bracket installed.Then at first the port engine would go into fwd after a 4 sec delay. Checked the oil pressure to GB, it was 100 psi.
    Checked the screen & found some clutch material, less than a teaspoon.
    Cleaned it, new gasket etc.
    Now there is NO transmission pressure. Port will not engage ANY gear.
    I have a mechanic who is going to help me re-build the oil pump.
    It's a HYDRECO Constant flow oil pump. I bought a new seal kit.
    IF the re-built pump still does not give transmission pressure, what else could it be & what should I do?

  2. #2

    Re: Allison Gear Box Problem

    Seems like it has to be the pump if there is no oil pressure. The pump is totally separate from the gear and the pressure is measured at the pump. The pumps are simple to repair, since they separate into two halves and you just put the 2 big O rings into the grooves and bolt them back together. One ring groove is round and the other is a 4 lobed star, but the ring starts out round. Good luck on fixing it. Hopefully the clutch stuff in the strainer doesn't mean going into the gear itself.

  3. #3

    Re: Allison Gear Box Problem

    Many thanks Nonchalant,
    I hope like heck you are right, I don't want the cost of removing a gearbox!
    I have removed the pump in the meantime and it turns with a lot of resistance, does this tell anything?
    Regards.
    Jasper

  4. #4

    Re: Allison Gear Box Problem

    I would check the reassemby and make sure you got all the lines correctly sealed. I have seen on this site before recommendations to make extra sure that your filter side and the seal to the transmission case down at the bottom were correctly sealed on reassembly. I also run 130 lbs of pressure on both M20s, which seems to be the common recommendation. That pressure is adjustable at the top of the pump with the tall hex nut with a keeper nut at its base.

    The Allisons are very durable and rarely break. I was advised that reverse takes much less fluid, so you will generally lose foreward first. Finally, there is an expert company down in southern Louisiana that rebuilds these pumps for Hydreco themselves, and will do yours for under $200, if I remember correctly. If you need help, I can search this site, where I found them originally.
    Kent Bracken
    "Sea Lion"
    1976 Bertram 42 Aft Cabin FB Motoryacht

  5. #5

    Re: Allison Gear Box Problem

    Quote Originally Posted by Genevatexan View Post
    I would check the reassemby and make sure you got all the lines correctly sealed. I have seen on this site before recommendations to make extra sure that your filter side and the seal to the transmission case down at the bottom were correctly sealed on reassembly. I also run 130 lbs of pressure on both M20s, which seems to be the common recommendation. That pressure is adjustable at the top of the pump with the tall hex nut with a keeper nut at its base.

    The Allisons are very durable and rarely break. I was advised that reverse takes much less fluid, so you will generally lose foreward first. Finally, there is an expert company down in southern Louisiana that rebuilds these pumps for Hydreco themselves, and will do yours for under $200, if I remember correctly. If you need help, I can search this site, where I found them originally.
    Thanks Genevatexan,
    If we can't get oil pressure and gear engagement by installing the new kit this week, then I will try to find a re-built pump. As I am in Australia, it would be easier to buy a Hydreco that has been re-built by the company you mentioned rather than send mine over to them and then back. I would appreciate it if you could let me know the name of the company that re-builds the Hydreco pumps. As for losing the fwd gear first, this makes sense: the fwd and reverse are both not engaging but before the pressure failed, it was the fwd that had a 4 sec delay while the reverse engaged immediately.
    Many thanks for your help.
    George

  6. #6

    Re: Allison Gear Box Problem

    The name of the company is Acadian Marine Transmission

    http://acadianmarinetransmission.com/site.php

    The have manuals and some pump information available for download on their site.

    The rebuild is much more than two gaskets. I had one of mine done by my local and it was about 15 gaskets and seals and other parts. MikeP posted pictures of his, you could probably do a search and find the thread where he posted them. Allisons exist all over the world, so I'd think you could source whatever you need there; sounds like your mechanic has the kit.

    Edit: here is blow up of a Hydreco from the Acadian FAQ section. Note all the seals and springs involved.

    http://acadianmarinetransmission.com...pbreakdown.jpg
    Last edited by GJH; 01-22-2012 at 07:42 AM.
    George
    Former Owner: "Incentive" 1981 56MY
    2007-2014

  7. #7

    Re: Allison Gear Box Problem

    The Hydrecos do wear out. the rebuild kit is just to reseal the pump. If you can, swap the pumps to see if thats a problem. I carry a spare pump with me. The Hydreco pumps have a hi failure rate, at least on SF I dont hear the Motor Yachet peeps complaining about it but they dont use the boats like we do. I've "loaned " my pump several times to other boats offshore. If you ever have to transfer a part at sea put it in an igloo cooler and duct tape the lid tight. Float it over rather than trying to get close and hand it to them.
    "DON'T BELIEVE ANYTHING YOU READ OR HEAR AND ONLY HALF OF WHAT YOU SEE" - BEN FRANKLIN




    Endless Summer
    1967 50c 12/71n DDA 525hp
    ex Miss Betsy
    owners:
    Howard P. Miller 1967-1974
    Richard F Hull 1974-1976
    Robert J. & R.Scott Smith 1976-present

  8. #8

    Re: Allison Gear Box Problem

    Many thanks to you all!
    the next few days I will be taking the pump apart and with the advice and help of a mechanic who I have known a long time, we will re-build it to the best we can and install the new kit.
    I will keep you all posted.
    Thanks,
    George

  9. #9

    Re: Allison Gear Box Problem

    Quote Originally Posted by rsmith View Post
    The Hydrecos do wear out. the rebuild kit is just to reseal the pump. If you can, swap the pumps to see if thats a problem. I carry a spare pump with me. The Hydreco pumps have a hi failure rate, at least on SF I dont hear the Motor Yachet peeps complaining about it but they dont use the boats like we do. I've "loaned " my pump several times to other boats offshore. If you ever have to transfer a part at sea put it in an igloo cooler and duct tape the lid tight. Float it over rather than trying to get close and hand it to them.
    Fishing certainly puts more work on the transmissions, but I don't understand how it would affect the Hydreco pump any more.
    George
    Former Owner: "Incentive" 1981 56MY
    2007-2014

  10. #10

    Re: Allison Gear Box Problem

    Quote Originally Posted by GJH View Post
    The name of the company is Acadian Marine Transmission

    http://acadianmarinetransmission.com/site.php

    The have manuals and some pump information available for download on their site.

    The rebuild is much more than two gaskets. I had one of mine done by my local and it was about 15 gaskets and seals and other parts. MikeP posted pictures of his, you could probably do a search and find the thread where he posted them. Allisons exist all over the world, so I'd think you could source whatever you need there; sounds like your mechanic has the kit.

    Edit: here is blow up of a Hydreco from the Acadian FAQ section. Note all the seals and springs involved.

    http://acadianmarinetransmission.com...pbreakdown.jpg
    Hi George,

    Maybe my pumps weren't Hydreco? I thought they were. They were original equipment on a 1978 53MY with 8V71TIs and Allison M20 gears. There are a lot of little gaskets, etc. on the fittings, but only the two big O rings in the actual pump body. Replacing those two fixed it completely.

    Regards,

    Doug

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