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Replacing front seal on TH350?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by gothamist, Apr 26, 2007.

  1. gothamist

    gothamist Registered Member

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    My transmission has been leaking since I got this truck (December) and now the leak is getting a lot worse. It seems to be coming out of the front of the case. I have heard that the front seal on the TH350 is a common problem...so, a few noobish questions:

    1) How hard is it to drop the tranny? Do I bring the transfer case (NP203) down along with it? I have a tranny jack I can use.

    2) What all should I expect to replace? The transmission works fine, it just leaks. I am thinking the front pump seal and the brass bushing? (This is what the Auto Parts store guy told me.) Are these just plug and play parts or do I need to get anything pressed in?

    3) Any pointers/suggestions are welcome.

    Thanks. :waytogo:
     
  2. southernspeed

    southernspeed 1/2 ton status Premium Member GMOTM Winner

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    If you have a PROPER trans jack, a strong 'tilt-able' wide cradle, then take the t/case and tranny down together. I've done it on my own several times but it one HEAVY combo!
    It's probebly (hopefully) just the seal. That's easy. The bushing I'm not familiar with.
    Be careful man, if that combo starts to fall, you won't stop it! Strap it down good.
     
  3. MA87K5

    MA87K5 1/2 ton status

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    I have rebuilt th350's before and haven't needed to replace the bushing unless it looked bad. The bushing has nothing to do with the seal. The seal can removed without removing the front pump from the tranny. If you can lower the tranny low enough to remove the convertor, then you can do it without lowering the x-fer case. Use something strong enough to use as a piviot point. Alot easier then dropping the tranny and x-fer case. I have done it so it can be done.
     
  4. gothamist

    gothamist Registered Member

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    Thanks

    Just wanted to say thanks for the information. This weekend I'll be diving into this so I'll see if I am smart enough to not need to drop the whole thing.
     
  5. bigblock72

    bigblock72 1/2 ton status Premium Member GMOTM Winner

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    While the trans is out remove the front pump and replace the o ring and gasket on the pump, they seem to leak more often than the converter seal. Removong the pump is fairly easy, remove trans, stand trans on end, remove pan and filter, remove bolts, thread in 3/8" bolts in tapped holes and hook slide hammer to bolts to remove pump. If you can't do it take it to someone who can. That's a lot of work to take a chance on, just bite the bullet and get all of the seals replaced, make sure you inspect the pump bushing once the converter seal is out. If the motor and trans are misaligned it'll burn one side of the bushing, generally very obvious.
     
  6. roadnotca

    roadnotca 3/4 ton status

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    and be sure to use a hefty ring to drive the new seal, same size as the seal.:D
     
  7. 76zimmer

    76zimmer Flyin Rat Premium Member GMOTM Winner

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    if the bushing is bad, it could cause a leak around the seal. If your going to pull the pump out, I would replace the bushing too. And you might as well pull out the direct drum and check the friction plates. How far you want to go?
     

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