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Leaky '48 Chevy transmission question

Discussion in 'The Hokey Ass Message Board' started by 48fleetmaster, Oct 15, 2010.

  1. 48fleetmaster
    Joined: Apr 28, 2010
    Posts: 65


    I have a VERY leaky transmission on my '48 Chevy Fleetmaster. It is the bone stock and original 3-on the tree trans. It operates perfectly, but it leaks all of the gear lube out within a couple of days. How hard is it to replace the seals in the transmission? Is it something that I could do myself or is it best left to the pros? Does anybody sell a complete seal set for these transmissions?

    Thanks for you efforts to answer me!
  2. Road Runner
    Joined: Feb 7, 2007
    Posts: 1,257

    Road Runner

    It's easy enough to do it yourself.
    You have to disconnect the u-joint and remove the transmission side cover, replace the seals/gaskets and re-assemble.

    Here are the parts:
    (you will only need one seal for the side cover)
    (this kit also includes gaskets for other transmission types available for these years, which will be left over)

    To replace the side cover/shaft seal, you will have to disassemble the mechanism, described in the manual.
    Here are the manuals that describe the steps:

    I included the 49-54 manual, because it has more detailed descriptions, especially for the u-joint ball gaskets re-assembly and proper adjustment.

    If the gasket of the clutch gear bearing retainer (see manual drawing) is leaking a lot, you will have to pull the whole transmission, to have access for replacement.
    But you can try to do the others first and see how that goes.

    Read everything first and if you feel comfortable doing this, buy the parts and have fun.

    And one more tip, regardless:

    Only use GL-4 rated gear oil in your synchro-mesh transmission.

    Avoid GL-5 gear oil. It has twice the amount of sulfur/phosphorous additive, which will slowly peel off the surface of the brass parts.
    You can confirm this, when you drain GL-5 oil after some use and the oil looks like thick metallic copper paint in direct sunlight.

    GL-4 rated gear oil is a little harder to find these days. NAPA stores have it.

    I also use this for my rear end, although GL-5 would be alright, since there are no yellow metal parts.

    Transmission and differential oil should be changed annually, especially in colder and damper climate zones.
    Last edited: Oct 15, 2010
  3. fordcragar
    Joined: Dec 28, 2005
    Posts: 3,179

    from Yakima WA.

    The hardest part of this job will be removing the transmission. If you have never had a transmission apart, this would be an excellent one to start with. Just be careful and don't force anything.
  4. G9mickey
    Joined: Jun 7, 2005
    Posts: 248


    I want to put a stick shift on my 48 Coupe. Does anyone know which one will fit/work best?
    Is there one I can take of another car or do I have to go with Hurst or some kit shifter?

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