Gear box leaking, how to fix?

[mrybas]

A Twin Disc Technodrive TMC 40P gear box is leaking ATF fluid from the rear (closer to the shaft coupling). Can anyone explain how to fix it?

[boatbod]

Remove coupling flange, dig out oil seal and replace.

[mrybas]

Originally Posted by boatbod

Remove coupling flange, dig out oil seal and replace.

Local mechanic said I need to remove the gear box....is that necessary? I guess I'll find out soon enough. I'm just trying to get my head wrapped around what I'm doing before I jump into it.

[Sailmonkey]

Originally Posted by mrybas

Local mechanic said I need to remove the gear box....is that necessary? I guess I'll find out soon enough. I'm just trying to get my head wrapped around what I'm doing before I jump into it.

Judging by the photo of your installation, yes you'll need to remove it from the engine.

[boatbod]

Originally Posted by Sailmonkey

Judging by the photo of your installation, yes you'll need to remove it from the engine.

Probably. There's not a whole lot of room to see what you are doing.

[Lepke]

Also look at the shaft where it rubs the seal. Sometimes salt water moisture will put small pits in the shaft that will make the new seal leak soon. There are sleeves made to cheaply fix this problem if it exists.

[barboak]

It probably has a 36mm nut on end of flange which needs to be removed to replace seal. The nut is thin, almost jam nut size, and easy to strip. I would remove transmission and use an impact wrench which makes the job easy! Good luck

[barboak]

Originally Posted by Lepke

Also look at the shaft where it rubs the seal. Sometimes salt water moisture will put small pits in the shaft that will make the new seal leak soon. There are sleeves made to cheaply fix this problem if it exists.

Very true as mine did and had a very small leak afterwards. Ordered a new output shaft and another seal and will deal with it when hauling boat for season in Puerto Rico, the sleeve sounds like a more inexpensive solution

[Diesel Bill]

Originally Posted by mrybas

A Twin Disc Technodrive TMC 40P gear box is leaking ATF fluid from the rear (closer to the shaft coupling). Can anyone explain how to fix it?Attachment 141469Attachment 141470Attachment 141471

Looks like you have a sacrificial disc between the output flange and the shaft coupling. Also looks like a 1-1/2" PVC pipe crossing over the coupling. Can this pipe be removed for better access? If you can remove the coupling nut and the cross over pipe and remove the sacrificial disc looks like enough room to pry out the old seal and tap in a new one. Clean up coupling where the seal rides on it with fine grit wet dry sandpaper dipped in diesel fuel. If grooved sometimes you can move the seal slightly in or out a little to position slightly in a different area.
As other posters said sometimes you just have to pull the unit to gain access.
I would try to do it in place then if you have to pull it at least you tried. The locking nut might be torqued up to around 200-300 lbs. ft. To me that would be the hardest part of the job breaking it loose. Good luck with it and let us know how it goes.

[Diesel Bill]

I forgot to add order a new lock nut. I believe it's a lylok style and should not be reused if possible to replace with a new one.

[mrybas]

Originally Posted by Diesel Bill

Looks like you have a sacrificial disc between the output flange and the shaft coupling. Also looks like a 1-1/2" PVC pipe crossing over the coupling. Can this pipe be removed for better access? If you can remove the coupling nut and the cross over pipe and remove the sacrificial disc looks like enough room to pry out the old seal and tap in a new one. Clean up coupling where the seal rides on it with fine grit wet dry sandpaper dipped in diesel fuel. If grooved sometimes you can move the seal slightly in or out a little to position slightly in a different area.

As other posters said sometimes you just have to pull the unit to gain access.

I would try to do it in place then if you have to pull it at least you tried. The locking nut might be torqued up to around 200-300 lbs. ft. To me that would be the hardest part of the job breaking it loose. Good luck with it and let us know how it goes.

I got everything slid out of the way. A 32mm socket fits on the nut at the end of the gear box, I'll try and break it free after breakfast and coffee🤞

[mrybas]

I got the nut off pretty easy and then the next piece (not the shaft coupler?) slid off pretty easy.
Any tips for getting the seal out without scratching the inner surface of the shaft housing?

[mrybas]

Got it out with nary an F-bomb or bloody knuckle! Now to try and find a new seal in bumble fark Panama!

[Diesel Bill]

Originally Posted by mrybas

Attachment 141506
Got it out with nary an F-bomb or bloody knuckle! Now to try and find a new seal in bumble fark Panama!

Good Job. Make sure to clean the bore where the seal sits really well and smear a light coat of permatex or equivalent on outside diameter of new seal before tapping into place. Try to find a socket or small length of pipe that fits over seal to spread impact over entire seal when tapping into place. If not then use a small block of wood so as not to bend (destroy) the new seal. Take your time and drive it into the bore squarely. Before installing the coupling smear some trans oil on the area the seal rides on to prevent dry start up and burning the lip of the new seal. Thats all I can think of at the moment.
If you can't find the seal, post the brand and mfg. part #s from the old seal and
I'll try to find one. Any good auto parts store should be able to match up a new seal as many different machines use same seals on different applications.
Keep us posted on how it goes.

[Brewgyver]

Nice work! I would have wanted to have a new seal (or two, if it was my 1st time) in hand before pulling the old.
Only thing I can add to the good advice above is to be very careful not to overfill the gear case once the seal is in. Add ATF few ounces at a time, and wait a few seconds before checking dip stick. Overfilling is the cause of many a failed seal.