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72 Blazer Automatic Trans/Transfercase

Discussion in 'Chevy Blazer Forum (GMC Jimmy)' started by Tybradley, Aug 13, 2014.

  1. Tybradley

    Tybradley New Member

    My son and I are restoring a 72
    Blazer and the transmission fluid is leaking over into the transfercase. We pulled the transfercase and checked the inner and outer seals on the thru-put shaft. We replaced the inner seal as it was damaged. We put everything back together and the problem still exists. We ordere a service manual and factory assembly manual and gained no insight as to the problem. I'm suspect that the seals may be in backwards. Stumped....any suggestions are greatly appreciated. My sixteen year old is anxious to get it on the road. Many thanks for looking!! Tybradley
  2. BurbanMan

    BurbanMan Member 1 Year 500 Posts

    Which tranny/T-case?
    TH350/TH400?
    Did you ensure that the seals were the correct size for the shaft before installation?
  3. DaCookie

    DaCookie New Member

    At the front of the t-case on the input shaft there are two seals. Today we use a doubled lip seal. On the two seal system, the inner seal seals fluid from the t-case from flowing into the transmission. The front seal towards the transmission seals the transmission fluid from being able to enter the t-case. ALWAYS replace them as a set. They are not cost prohibitive considering the labor involved to redo the job.

    Assuming you do have the correct seals, and you didn't bugger up the sealing surface of the shaft or the mounting bore of the seal, you should simply be able to drop the t-case and install it.
  4. DaCookie

    DaCookie New Member

    As far as the seals being in backward. When looking into the front of the t-case with the seals correctly installed, you are looking at the back of the first seal.
    If you remove the first seal, you are now looking at the face of the inner seal. Make sense?

    Think of it this way. If it were a two wheel drive transmission it would have a tail housing with an output seal as the transmission fluid is slightly higher pressure inside the trans than out. The front seal on your t-case is actually the important one here being as it is effectively the transmission output seal. The innermost seal on the t-case input is the input seal for the t-case. T-case fluid is at asmospheric pressure usually so it is much less important in this scenario as long as the t-case isn't over filled.

    I really hope this makes sense. I would like to know the t-case numbers so I could check and make sure it's not just a problem inherent to that particular design, but I can't recall any sort of problems like that from back then, other than what has been discussed. There could be a small stress crack in the t-case housing or something odd though.
  5. DaCookie

    DaCookie New Member

    I was looking at the core pile today and saw a 350 case from a job last year I hadn't thought of last night. What model t-case is it? Is it cast iron or aluminum? The old cast iron ones were bad about breaking offthe back end of the transmission case. If this ever happened to yours, assuming it's the cast iron one, you really should pressure wash it and check it thoroughly for cracks aaround the input shaft.

    Good luck.

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