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th400 tp np205 problem B&B??

Discussion in 'Chevy Trucks' started by Detroitdan, Mar 14, 2010.

  1. Detroitdan

    Detroitdan PlowSite.com Addict
    Messages: 1,937

    Finally got around to changing the flexplate on my project truck, while I was under it I saw the tranny/t-case was a little leaky. Changed the filter and pan gasket in case that was the problem. Tranny pan had plenty enough in it. Decided to check the level in the t-case and woo-hoo! atf shot out a good five feet! It was so overfull it had to be right to the top of the case, I probably took a gallon or two out of it just to get it to the full line. First I was scared beause I didn't think it was supposed to be atf, but I checked and it is. But the more I thought about it I just can't see how someone could have overfilled it so much. So it has to be a seal between the two units is gone, and the tranny is pumping fluid right into the transfer case. I put 4 qts in the tranny and it didn't show up on the stick, added two more and it showed and I could move it out of the shop.
    I'm guessing the previous owner must have just kept adding tranny fluid to it so the tranny didn't run dry and fail. I'm going to attempt to pull the transfer case back and change the seal. Anybody heard of this happening, and how hard of a job is the seal to do? Is the tranny and transfer saveable? They are supposed to be pretty rugged units.
     
  2. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    Sure they were famous for the seal failing thus allowing the ATF to migrate into the T-case and grossly overfilling it. Some get so bad they'll spew it from the T-case vent. :eek:

    Easy fix though, slip the T-case out and you'll see the seal in the adapter housing. There's several different variations so be sure to make an attempt to salvage the old seal as much as possible during removal for references purposes with getting the correct new one.
     
  3. Detroitdan

    Detroitdan PlowSite.com Addict
    Messages: 1,937

    Thanks B&B!
     
  4. Detroitdan

    Detroitdan PlowSite.com Addict
    Messages: 1,937

    OK, just pulled the transfer case off, there is a seal at the back of the adaptor housing. Looks like there may be one at the front too, on the trans end. DO I need to worry about that? Obviously the one at the transfer case end is gone, otherwise fluid couldn't pass thru. Visually it looks ok, but I know it isn't. Haven't removed seal yet but parts store has one listed by application, no way of knowing yet if it's right. Any special trick to removing it? Or just pry it out like a wheel seal?
    Thanks
     
  5. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    Which style of drive is it? Is the T-case input female and splined directly to the trans output? Or, is it male with a separate drive sleeve in the adapter housing tying the input and output shaft together? They came in both styles depending on year.

    If it's directly mated without a separate sleeve then there's only one seal and it's the one you can see. If it instead uses a drive sleeve there may or may not be an additional seal at the front (depends on age), but there should be a bearing.

    But regardless of how many seals there are change them all now, no point in doing it again to get at the other you didn't do at a later date.
     
  6. Detroitdan

    Detroitdan PlowSite.com Addict
    Messages: 1,937

    t-case is female, there is a splined input shaft coming from the transmission. So there's just the one seal?
     
  7. NICHOLS LANDSCA

    NICHOLS LANDSCA PlowSite Veteran
    Messages: 4,303

    Sounds like the single seal.
     
  8. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    Yep, single seal and no support bearing in the adapter.