Th400 mated to np241 seal issue

[Jay74]

I have a TH400 followed with a Np241. I noticed the tranny not keeping fluid and the t-case leaking everywhere. After a bit of research I realized there should be an output seal on the tranny and an input seal on the t-case both needing to be replaced. Seemed simple enough.

Brought down the case and it looked as I expected. The trans on the otherhand has no seal, nor does it look like it has a place to put one. Did the PO rig these together somehow where it was destined to fail from the start. Or is this a normal issue and a standard way to mate these two units. I'd hate to replace the input seal and refill everything just to have it all leak again.
Guidance is needed and appreciated

 

[sweetk30]

gm trans of this style have no output seal .

there is a large rubber o-ring around the t-case adaptor to tranny body . also there is a gasket between the t-case adaptor and t-case body .

otherwise check for hair line crack in adaptor and back of tranny .

but if the seal on the t-case input is old hard weak it will let fluid push past and over fill the t-case .

and a np-241 takes atf fluid . NOT gear oil .

 

[Hogback Fabrication]

There is no output seal on a TH400. The only thing keeping the trans and t-case fluid separate is the input seal on the t-case.

 

[Jay74]

It looks as if the t-case was leaking simply because it so over filled. So it would seem a new input seal for the case and a new gasket where the case and adapter meet and I should be golden.

 

[Joe In Montana]

I did an all straight cut transfer case gear conversion and the instructions were to not use the intermediate seal. The ATF freely circulates in both the 700 and the transfer case, although it doesn't move back and forth between them very fast.

At first I thought this would be a big mistake, and called the vendor and he said to just do it that way. I believe these straight cut planet sets were military on some of their transfer cases and the vendor bought a boxcar full of them surplus.

At $75.00 a set, I bought six or seven, and sold two sets, installed in customers' 4WDs, to recoup my initial cash-out. I now wish I'd have bought ten more sets. IIRC, I put a set in a Jeep Grand too. There's still a couple of sets in my garage in the original sealed olive drab packages for spares - just in case.

So far after 20 years they've been this way and everything's going good. I've just got to make sure the vent hoses are clear and routed high to the back of the firewall and the speedo drive has two shaft seals on the output. They fit just fine in the stock drive aluminum housing and since I can only get plastic driven gears, this helps them live a lot longer.

I use my K5 mostly to haul 3+ cords at a time of Larch out of the Montana high country on my 8 x 20 three axle trailer a few times a year after the first snow. I usually am in 4WD with the hubs locked from about this time of year until late April or so.

I like to go out for a couple of days, overnight, and camp in the snow with my wife and another couple. We fish a lake or two for fresh trout while we're at it.

Thus far I've had no troubles at all other than a couple of worn out speedo gears.

I also change the fluid and service the trans filter every couple of years .... and yeah....it takes a lot of ATF..... and they really sing out loud in Low Range --- (it scares the Grizzlies away) .

If my results without the seal, and if the fluid is full in the transmission and there's no leaks - then what's the big problem ?