Twin Disc Transmission fluid leak.... any advice?

[Frank Langer]

Hi,
The Twin Disc MG340 transmission in our boat has been working well since 2009, 1800 engine hours since installation. Today I noticed tranny fluid dripping at a rate of one drop per two minutes while running in gear, leaving a sizeable mess after running for a while. I was able to top up the fluid before it got too low, so don't think there is any damage to the transmission itself. The leak is at the front end at the bell housing, perhaps just to the left of centre, though it's hard to tell. I'm guessing that there is a seal there that is giving way to cause the leak, and that the transmission will have to come out and either the seal replaced, or a new transmission installed. Has anyone encountered this with this or a similar transmission, and if so, any advice on whether the seal can be reasonably replaced, or is that just a future problem waiting to happen. Any advice on how that tranny is removed from a Universal Diesel model #5416? Any other advice on how to proceed. I have phone calls in to various places, but am not getting much response, especially in these "social distancing/work from home" times.

Interestingly, this leak developed on just a second brief outing after having the PSS dripless shaft seal replaced, which requires that the transmission coupler be removed. The mechanic had a hard time removing the coupler from the prop shaft, using bolts between the coupler and the transmission flange and a spacer to gradually force the coupler off. He insists that a leak at the other end of the transmission is unrelated to his work. Hard to tell, and even harder to prove, I guess.

Thanks for any comments or advice!
Frank

 

[Rocinante33]

Unrelated to his work? Yeah, right.

i don’t know the twin disc tranny but the seals may have hardened and then jostling of the shafts led to the leak. Maybe try some Lucas Oil transmission stop leak. It helps to recondition dry seals. Worth a try, I think.

 

[Pat C.]

On an M25 Universal the transmission bolts to the bell housing from inside the bell housing, which means the bell housing has to be removed. Mine has a Hurth transmission, so apples to oranges, but likely the same for all transmissions. I had to do this last year because the bell housing motor mount broke, ended up pulling the engine to do it. Made like easier overall I guess.

Hopefully I'm wrong in your case, but sorry in advance if I am. Maybe the stop leak will work so you don't have to worry about it.

 

[Frank Langer]

On an M25 Universal the transmission bolts to the bell housing from inside the bell housing, which means the bell housing has to be removed. Mine has a Hurth transmission, so apples to oranges, but likely the same for all transmissions. I had to do this last year because the bell housing motor mount broke, ended up pulling the engine to do it. Made like easier overall I guess.

Hopefully I'm wrong in your case, but sorry in advance if I am. Maybe the stop leak will work so you don't have to worry about it.

Hi,
Thanks for your replies. I lost some sleep over this last night, but was able to talk with a Twin Disc service centre today, and within an hour they had sent a mechanic to "take a look". He diagnosed a leak in the seal at the shifter, not at the bell housing as I had thought. He said that because it always shifts forward, neutral, reverse, that area wears and then the seal dries out over the years and it leaks. No way to avoid that, he said. In a half hour he had the shifter removed without having to remove the tranny, will order a new seal, and reinstall next week when the seal arrives.
I think I got lucky on this one, with no need to remove the tranny from the boat to fix it.
Mechanic said the MG340 is a good transmission, as long as it is maintained with regular fluid changes.
Frank