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Old 19-11-2014, 20:12   #1
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Twin Disc transmission breather

Hi all,

My Twin Disc TMC40 transmission has a breather that is severely corroded and needs replacing. Instead of trying to find an OEM style replacement part, I want to install a brass nipple and a length of tube instead. I'd like to find out what the thread spec is. I'm guessing it might be 1/8" BSP but being Italian made, it may be something else. Any wiz's out there know what it might be?
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Old 20-11-2014, 07:09   #2
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Re: Twin Disc transmission breather

M10 by 1.0.
I suggest that you just buy the correct item.
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Old 20-11-2014, 07:37   #3
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Re: Twin Disc transmission breather

Can you remove it and take it to the store to compare? I normally recommend the "correct" part myself, but a breather fitting? I think I might even go with the white plastic
nipple. I call it nylon, but have no idea what it's made from, if the thread isn't right, you won't damage the transmission case and it's unlikely to corrode.
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Old 20-11-2014, 07:54   #4
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Whilst it would be nice to buy an off the shelf replacement, no one in my neck of the woods or even the marine engine dealers further afield seems to supply them as spares. Plus the fact they are made of steel makes me suspect they're a standard diff breather. Using a nipple and tube is a common method of raising the breather intake away from water ingress sources and the hint here is my breather is rusted away. My 4 wheel drive has a similar system as standard so I'm looking to improve on oem.
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Old 20-11-2014, 10:43   #5
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Re: Twin Disc transmission breather

M10 Banjo Bolt | eBay

NC poster says it is M10 x 1.0 metric thread hole.Perhaps a banjo fitting would work.Google & try to find a SS or brass one with a hose barb.
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Old 20-11-2014, 15:49   #6
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Re: Twin Disc transmission breather

Quote:
Originally Posted by NCboatrx View Post
M10 by 1.0.
I suggest that you just buy the correct item.
Just realised from the another thread you are an authoritative source! Thanks for the spec. Here's why I want to do away with the standard breather. It's mounted directly atop the case adjacent to the filler plug. Aside from the breather, the gearbox is water tight. In a situation where a narrow and shallow bilge takes on water the incline of the engine can allow the shaft coupler to splash water over the transmission and the location and height of the standard breather exposes it to this splashing, risking water ingress into the transmission (especially at the moment as the steel cap on the breather has dissolved into rust flakes!).

Our boat has a narrow and shallow engine bilge, and whilst it has never happened to me because I look after my boat (well, except on first launch after purchase ), the PO's apparently had problems keeping water out of this area. It only takes about 10 litres of water for the problem to occur on this vessel. Having said that, I can see a failure of the prop shaft seal or leaking raw water system has the potential to cause the issue in a short space of time. With a modified breather it will be impossible for water to enter the transmission as once the water reaches a certain level it will spill over to the main bilge. We purchased the boat with 19 engine hours and even now 12 months later I'm still a little concerned there may be some water induced transmission damage as the transmission makes a noticeable click/clunk sound when engaging forward gear (reverse is fine). I installed a new Beta from scratch in our last boat that by coincidence had the same model transmission attached and don't recall having any issue in this regard.
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