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Auto trans choices for sbc ?

Discussion in 'The Hokey Ass Message Board' started by orphanautomill, Feb 27, 2011.

  1. orphanautomill
    Joined: Jun 21, 2010
    Posts: 156


    I've read up on this some, but there is still some mystery here to me. Not being a GM guy at all, I'm looking for some advice here.

    Previous owner installed a 350/350 into my truck. The 350 trans is leaking like crazy, but seems to shift fine and be OK otherwise. It will need to be pulled to fix the leak, so I'm wondering if there is a better choice to put in there now and just replace it (TH400 / 700R4 etc)? OD would be nice, but not critical. Either seem to be cheap and plentiful in the area.

    I would rather not mess with the driveshaft at this point, but I don't know if the lenghts change or not.

  2. BELLM
    Joined: Nov 16, 2002
    Posts: 2,588


    I would pull the TH350 and fix the leaks. If the pump/converter seal is not leaking you could probably fix the leaks without pulling the tranny. Clean it good, find the leak. TH 350 is a good transmission, if it is working good but just leaking I wouldn't replace it
  3. Hnstray
    Joined: Aug 23, 2009
    Posts: 11,474

    from Quincy, IL

    The 400 will require a driveshaft and crossmember/rear mount alteration and uses somewhat more horsepower to run it. The easiest choice for minimal alterations is the 2004R...same length as 350, mount is a bit farther back, but not by much and output spline is same as 350 turbo. The 700R4 is a good trans, but is longer than a 350/2004R. Hope this helps. by the way, your rear end ratio is a factor in this decision too. You would find and OD automatic will work best for most applications with a mid to upper 3's (i.e. 3.25 to 3.73) range to allow for adequate power when in OD.

    Last edited: Feb 27, 2011
  4. orphanautomill
    Joined: Jun 21, 2010
    Posts: 156


    I think it is the converter seal, but even so this is probably the best route.

    Sometimes it's helpful to get confirmation on what I think is the best choice just to get me back on track and make some progress.

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