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Th400 Speedometer issue

Discussion in 'The Hokey Ass Message Board' started by 35mastr, Jul 29, 2012.

  1. 35mastr
    Joined: Oct 26, 2007
    Posts: 1,899

    35mastr
    Member
    from Norcal

    I crawled up under the Hudson to hook up my speedo. Only to find that this TH400 never had a provision for one. I am told it was run off the front wheel when it was in a Olds.

    My question is has anyone here run into this and figured a way to get the speedo to work without tearing the trans apart?
     
  2. Bad Banana
    Joined: Jun 20, 2008
    Posts: 834

    Bad Banana
    Member

    Yep... run into this. No easy fix. That speedo hole is precision machined and you would play hell trying to machine it even if you stripped the case. Find another case with the hole and swap your guts over is the easiest way. I just did this for a guy last winter on his TH400.
     
  3. 35mastr
    Joined: Oct 26, 2007
    Posts: 1,899

    35mastr
    Member
    from Norcal

    I was hoping that I could swap the tailshaft with one that had the provisions for a speedo.
     
  4. Bad Banana
    Joined: Jun 20, 2008
    Posts: 834

    Bad Banana
    Member

    Look again. The speedo is not in the tail housing. It is in the main case.
     

  5. 35mastr
    Joined: Oct 26, 2007
    Posts: 1,899

    35mastr
    Member
    from Norcal

    Yes its in the case. I was wondering if I could use a tailshaft that has the provisions for a speedo with a reluctor ring such as VSS. I have an Electric speedo from Classic Instruments.
     
  6. squirrel
    Joined: Sep 23, 2004
    Posts: 55,942

    squirrel
    Member

    if you have an electronic speedo you might be able to use an old driveshaft magnet sensor for a cruise control
     
  7. Bad Banana
    Joined: Jun 20, 2008
    Posts: 834

    Bad Banana
    Member

    Sorry... I missed it where you said you were using an electric speedo? :confused:

    Being on a traditional hot rod website I "assummed" you were trying to hook up a cable speedo. (my bad):eek:

    That changes stuff. Maybe find a different tail housing and look at it to see if you can use a reluctor and speed sensor from a 4L80E. Mock it up and see if you can machine the tail housing to fit the sensor. It may even be able to go where the original gear went on the main case. Being an electrical sensor vs a mechanical gear, you could probably get away with drilling it yourself. Probably could be done. Depends on how bad you want it.
     
  8. squirrel
    Joined: Sep 23, 2004
    Posts: 55,942

    squirrel
    Member

  9. The olds was not electronic, it just had the drive built into the front spindle. It can actually be adapted to any number of cars with a little work.
     
  10. chubbie
    Joined: Jan 14, 2009
    Posts: 2,336

    chubbie
    Member

    last time i looked there is a "boss" where the speedo bung would be. looks like you just tap on the thin aluminum filler, and pop it out and its there. never looked inside if the output shaft has the "threads" for a big speedo gear. it uses the large cover. might have to tap the hole for the small bolt, but the hole is there
     
  11. chaos10meter
    Joined: Feb 21, 2007
    Posts: 2,191

    chaos10meter
    Member
    from PA.

    You can buy one of them GPS sending units for about 100 bucks.
     

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