Dana 20 full of ATF

[440sixpack]

My 1978 J10 project is about 3/4 done and now I'm puking ATF out my transfer case on the floor.

I have a TH400 converted to accept the Dana 20 with factory parts. I assume there must be a seal that is either bad or missing between the adapter and the transfer case ? since my TSM doesn't cover this combination I don't have anything to go off of.

[rang-a-stang]

Can you verify the ATF level in your trans is going down? Does D20 take ATF or gear oil? I guess what I am getting at is: are you sure where that ATF is coming from?

[KaiserMan]

There are two seals in your transmission to transfer case adapter. One on each side of a large bearing. Sounds like both are bad.

Edit. Seals are both on one side of the bearing.

[440sixpack]

Yes, my transmission is low enough it won't hardly move.

I pulled the case and adapter and one of the seals is shot, the other looks okay. I'll replace both of course.

The next thing is I've seen talk on the web about an O ring on a chevy that must be in place or it will leak. on the input? I don't know where.

I would assume a chevy with a TH 400 and a Dana 20 would be basically the same set up. but I can't confirm any of this. I wish I had a TSM from the early 70's.

[mattmopar440]

well if you didnt put ATF in it its comming from the TH400 the TH400 has no output seal so the input seal on the Dana 20 is bad

[440sixpack]

There are 2 seals in the adapter to hold in the ATF, the Dana 20 is wide open. so those seals I understand.

I still don't know about the O ring or where it goes or if there is one. it looks as if ATF could work it's way between the gear splines on the TH 400 output into the Dana 20. somewhere here is where I think the O ring come into play.

[bufurd]

The o ring is on the output shaft in a groove to keep atf from going through the splines. I've "siliconed" up the splines when I put t case on in past and never had an issue

[mokurt]

My old '67 was leaking the same.
I replaced the seals in the adaptor,replaced adjacent gaskets/orings and siliconed the splines.

[440sixpack]

There is a groove on the output shaft with no O ring on it. no doubt this is the problem. I'll put one on as well as silicone. since I have it apart I'll put new seals in the adapter.

hopefully this will help someone in the future, I searched hard and there seems to be very little helpful information on this issue .