Velvet Drive: How to Separate Reduction Housing from Gearbox?

Discussion in 'Propulsion' started by crwsound, Aug 5, 2018.

  1. crwsound
    Joined: Apr 2012
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    Location: Seattle, WA

    crwsound New Member

    Hi, I'm starting to rebuild my 10-18-004, which is a 72C velvet drive with a 1.52:1 reduction gear. I've read a lot about doing this rebuild, and given the symptoms I encountered last year, I believe the reduction gear is fine and I'm not rebuilding that - just everything in the forward/reverse transmission case (which I'll call the "main gearbox" from now on).

    My question is with the simplest thing (I think), separating the reduction case from the main gearbox. I've pulled all of the bolts that connect the reduction housing to the gearbox, and of course it won't budge. What I really need to know is - does this just want some PB Blaster and hammer-y encouragement to come apart? Or is there more to it than that, say, taking the gearbox apart from the pump end and once I get down deep into the gearbox then I'll be able to release the reduction housing by taking a snap ring off of something? Or is it taking the coupler nut off of the end of the reduction case and then the housing pulls off and THEN I'll be able to release all of the reduction gears from the main gearbox?

    I read through the "SERIES 10-17 AND 10-18 SERVICE INSTRUCTIONS" in the "Velvet Drive Installation Manual", as well as other instructions in other manuals, but I couldn't find an answer to this question.

    Thank you all for any help you can offer,
    Chris

    ps. For people that want to know what symptoms I encountered last year: nothing leaked, and the trans ran fine in reverse - smooth, quiet, efficient. It also ran fine in forward, BUT it was noisy (like a whine made up of grinding sounds) and I didn't want to run it very long or very hard. The transmission fluid, now drained, doesn't smell bad, nor did it become discolored...in other words, I don't think it burned. But then, I was gingering it in forward. Thanks again.
     
  2. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    You need to remove the nut at the end first.
     
  3. Barry
    Joined: Mar 2002
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    Barry Senior Member

    Was there any changes done to the drive line before the noise presented itself. Ie cutlass bearing changes, or anything that could have resulted in a misalignment between the shaft and
    transmission? A misalignment can make the transmission extremely noisy. Is there a Vdrive attached?
    You can easily download parts breakdown for the transmission and see if there is in fact a clip that is holding the thing together.
    And there are actual rebuild manual, not service manuals that would help you through the process.
     
  4. baeckmo
    Joined: Jun 2009
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    baeckmo Hydrodynamics

    Start with checking the forward thrust bearing before taking it all apart!
     
  5. crwsound
    Joined: Apr 2012
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    Location: Seattle, WA

    crwsound New Member

    Thanks Gonzo, that's how I was leaning, but I didn't want to take off anything I didn't have to.

    Barry, indeed there were totally changes done to the drive line before the noise! The boat was new to me a few years ago with a known blown engine, so the first thing I did was pull that and rebuild it from the block up. Engine runs like a top now. I did replace the cutlass bearing as long as I was working with the drive train, and last year I originally suspected that I had misaligned the shaft/transmission when I reinstalled everything. But after fighting that to get it perfect a few different times, and with the fact that everything ran perfectly and quietly in reverse, I eventually came to suspect that the transmission needed rebuilding. Especially since the prior owner had mentioned that he'd been inclined to replace both the engine and transmission.

    I have downloaded a few different velvet drive manuals (including the service manual) and looked through them all, also scouring the diagrams...I imagine somebody more familiar with a transmission would have been able to easily see the answer in front of them, but I couldn't, hence the question. In the part of the service manual that described rebuilding my reduction gear I just couldn't tell for sure whether or not I really needed to take the entire reduction gear apart in order to disconnect it from the main gearbox. I was hoping I didn't have to do that, now I know that I do.

    And just to round out the info: 28' Tollycraft with a Mercruiser 5.7 litre, the transmission is NOT a V-drive.

    Thanks.
     
  6. crwsound
    Joined: Apr 2012
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    Location: Seattle, WA

    crwsound New Member

    Hey Baeckmo, just saw your response. As I mentioned, the previous owner had said he'd thought about replacing the transmission (didn't say why though), and I've got the kit of parts to do the rebuild, so I'm just going to go ahead and do the work.
    Thanks,
    Chris
     
  7. MikeJohns
    Joined: Aug 2004
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    MikeJohns Senior Member

    You get those sounds often from a worn output bearing. They are a standard bearing and with the seal cost me around $30. Try and get seals out so you can read the code on them !

    Attached is a snip from the 71c service manual


    Added [ Duh... I see it's already been mentioned ]
     

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  8. MikeJohns
    Joined: Aug 2004
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    MikeJohns Senior Member

    I think that's just because it's too hard to loosen it later.
     
  9. crwsound
    Joined: Apr 2012
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    Location: Seattle, WA

    crwsound New Member

    Thanks Mike. Here's probably a stupid question, but I'll go ahead with it.

    I've looked in the rebuild manual more than a little, and to me it seems like there are output bearings in both the main gearbox and the reduction gearbox. Both you an Baeckmo said to check the output bearing (or in Baeckmo's case, the forward thrust bearing)...and I don't know which of these bearings I'm supposed to be looking at. What I THINK is that it's the more forward of the two "bearing cone" bearings (that's how the manual refers to them) that's right near the aft end of the reduction housing. Is that correct?
     

  10. MikeJohns
    Joined: Aug 2004
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    Location: Australia

    MikeJohns Senior Member

    The final output bearing one step from the reduction box output flange.
     
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