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  1. #1
    Join Date
    Aug 2018
    Posts
    9

    Default Drive shaft coupling leaking

    I'm new to this forum. And I'm recently a new Moomba owner. Last month I bought a new to me 2005 Mobius LSV. This is the first inboard boat I've ever owned.

    We've had it out a couple of times now and I'm having an issue with the bilge kicking on every 15-20mins. Yesterday I pulled the V-drive cover and saw a steady stream of water leaking from the drive shaft coupling (I'm attaching a pic). This was with the boat anchored and engine off. I've read up on some posts about the shaft packing seal leaking but that would be the brass nut lower down where the shaft exits the boat. This coupling is up near the V-drive. Why would that coupling be leaking? Does water come up through the shaft to that coupling or come from the V-drive to that coupling? Or is there something else near that coupling that might be leaking onto the coupling making it look like the coupling is leaking?

    Also, if my bilge is keeping up is it still ok to use the boat like this? Obviously if it gets worse I would stop and I would only be trailering, never leaving it in the water.

    Any help or experience anyone has would be greatly appreciated. Thanks.
    Attached Images Attached Images
    2005 Moomba Mobius LSV

  2. #2
    Join Date
    May 2003
    Location
    south east michigan
    Posts
    308

    Default

    It appears the shaft packing is leaking so bad it shoots a stream of water all the way up and hits the coupling making it appear to leak.You need to tighten up the shaft packing.There are two nuts,the big one and a thinner one next to it to lock the big one down.Hold the big one and back off the thin one,then tighten the big one until the coupling drips one drop every 30 to 45 seconds.If it wont tighten enough the packing needs to be replaced.
    jy

  3. #3
    Join Date
    Aug 2018
    Posts
    9

    Default

    Thanks for the quick reply. The small packing nut is all the way bottomed out so I'll have to replace the packing seal.

    Any recommendations on what kind to use? I've read there is a rope type and also a synthetic type. Any opinions on what is best? Also, what size is the packing nut, I want to make a custom set of wrenches to fit in that tight space better. Thanks.
    2005 Moomba Mobius LSV

  4. #4
    Join Date
    Mar 2003
    Location
    Springfield Missouri
    Posts
    3,391

    Default

    The synthetic cord doesn't melt, doesn't need replacing, doesn't need to have water dripping. The 13 years I used the graphite cord, I tightened the nut once. Since that install, Teflon cord became available and have the same characteristics. I'm not sure why wax cord still exists.
    1998 Mobius
    310 HP PCM
    SOLD

  5. #5

    Default

    Use the teflon packing material. It is much better. Make sure you buy the right size packing for your nut/shaft because only the correct width of packing will fit. I'm guessing you will need 1/4 inch packing but I'm not 100% sure. Also, get yourself a packing extractor. It is an $8 tool and makes the job 10x easier and faster. It looks sort of like a corkscrew. It will only fit in one side of the nut, so you will know which side of the nut to pull the packing from.

    You should not need a wrench for the packing nut. It should only be hand tight. If the packing nut is tighter, it can cause the packing material to press too hard into the drive shaft and score the shaft (which causes more leaking). Point is, you should be able to loosen it by hand. If not, a pair of channel lock pliers should do (a large pair). There is actually a second nut the packing nut wedges up against - (it turns in the opposite direction) you need to loosen the packing nut while holding or turning the other nut in the opposite direction. In other words, if you tighten both nuts they will approach each other until they both stop. It is the large packing nut doing all the work to keep the water out of the boat. The other nut just keeps the packing nut in place.

    The packing nut is hollow and should be partially filled with packing. The packing looks like rope dipped in wax. You want to cut the rope (packing) to lengths that will form a ring around the shaft (like a belt around your waist). On my old boat I used 2 to 3 rings, you may differ. Cut the packing on a 45 degree angle and stagger the cuts as you wrap your rings around the shaft and insert them into the packing nut. MAKE SURE YOU PUT PACKING GREASE ON THE PACKING BEFORE YOU PUT THE PACKING INTO THE NUT. Don't just wrap the shaft a few times with one big piece of packing rope -- it will leak. Tighten the nut back up a about a turn or two and put the boat back into the water. You will want to look at the nut and tighten it 1/4 turn at a time until water stops dripping in the boat through the packing nut. The ideal packing will drip once every 10 seconds while the shaft is turning and not at all when in neutral.
    2020 Supra SE 450

  6. #6

    Default

    I'm looking at that picture again and I'm not 100% sure the leak is coming from the packing nut. What is the large hose next to he shaft? Is that hose cracked and shooting water at the shaft?
    2020 Supra SE 450

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