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Need advise on SM 465 trans.

Discussion in 'The Garage' started by Eric M., Sep 8, 2005.

  1. Eric M.

    Eric M. 1/2 ton status

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    Location:
    Oakland, CA
    I just bought a 1980 GMC C3500 dump truck (work truck). The trans will shift throught the gears when the engine is off, but not when it's running. Where ever it is when you strat it up, that's where it stays, clutch in or out. If you put it in first, push the clutch in and start it, it lerches forward. If you start it in neutral and rev the engine, you can hear something rattling around in the bellhousing. I believe it is a SM465 (4 speed, granny low).

    1. Any ideas as to what's wrong?

    2. Any good tech articles for working on this trans? I've never worked on a manual before, anything would help.

    Thanks,

    Eric M.
     
  2. big83chevy4x4

    big83chevy4x4 3/4 ton status

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    sounds like a clutch problem, not disenguaging.

    check the freeplay in the clutch petal, should be 1/4" at the petal. then check the clutch fork is on the stud in the bellhousing. if its not those you need to pull the tranny.
     
  3. Seventy4Blazer

    Seventy4Blazer 3/4 ton status

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    i agree fully.
    Grant
     
  4. mountainexplorer

    mountainexplorer 1/2 ton status

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    If it's not a linkage, clutch rod adjustment, or arm issue, it could be the disc itself went bad. When I first bought what we call the Truck Blazer, it did the same thing. No noise, just no clutch response. One of the springs in the disc had come out and lodged itself between the disc and the flywheel locking them together.
     

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