700r4 Output Leak

Discussion in 'Transmission & Driveline Topics' started by Canuck71z28, May 17, 2018.

  1. Canuck71z28

    Canuck71z28 Veteran Member

    Mar 8, 2008
    Ottawa, Canada
    Hi, I have a '67 C10 that has had a fluid leak at the output seal on tranny since I've had the truck. I just had the drive shafts serviced and balanced, u joints checked, and new hanger bearing installed due to a broken hanger bearing. At the same time, I installed a new bushing in the tail piece and installed a new output seal. The area of the yoke that the seal rides on is smooth. Well, I still have a leak from the output seal, any ideas? Thx, Mike
  2. CorkyE

    CorkyE Veteran Member Lifetime Gold Member

    Nov 4, 2004
    Ringgold, GA
    Can you determine if it's leaking around the area where the seal goes into the tail shaft or around the driveshaft yoke? If around the tail shaft, it may be warped or not machined correctly. Depending on how bad it is, you can try coating the housing with RTV before putting the seal on. Good luck, I hate leaks.
  3. black_aerocoupe

    black_aerocoupe Veteran Member

    Some yokes have access to bolt in, so they could leak there. Also, a yoke with a plug in back could leak. You did a fair bit of work. Now, spray soap on and rinse clean. Once dry, put talcum powder over it, and you'll find your leak.
  4. Coadster32

    Coadster32 Veteran Member Lifetime Gold Member

    Oct 2, 2013
    If it's a seal/yoke leak, you may consider a double lip seal.
  5. camaro71/holland

    camaro71/holland Veteran Member

    Aug 27, 2003
    The Netherlands
    If you consider to put a new seal in, put some RTV on the seal, not in the housing (or you'll be pushing it in) and run a fine grid sand paper over the yoke to make it perfectly smooth (across not in length).

    Make sure the trans is not overfilled. During operation some excessive oil will go to the converter, but at rest you can experience converter drainage overfilling the transmission with oil looking for a spot to escape.
  6. jthomas

    jthomas Veteran Member Lifetime Gold Member

    Dec 5, 2007
    NorthCentral PA
    It is not uncommon for the tail shaft seal bore to get scored when the old seal is pulled out. The seal puller can gouge the bore if not used properly. If that is the source of the leak, some RTV or Great Stuff sealant in that gouge, and a new seal, can stop the leak.
  7. black_aerocoupe

    black_aerocoupe Veteran Member

    There are no single lip seals.

    The flat style seal you'll buy at the parts store is a double lip style; the two I. D. seal surfaces are part of the same seal material.

    The "uncircumcised" style more common on late models is a triple lip style. The outer, third lip is a dust seal only. It lacks sizing tension, spring support, and contact area to help with any lubricant sealing and will not solve leaks if the old seal is not faulty.

    In this case on the smaller, 27 spline GM seals for the yoke, seals are seals. But I will admit T56 customers like to see the uncircumcised style as it gives an "OEM" appearance.
    Coadster32 likes this.

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