1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.

mating a 81 3b motor to a 78 bj40 transmission

Discussion in 'Diesel Tech / 24 volts' started by mike, Aug 2, 2005.

  1. mike

    mike 82bj42 1st project

    Messages:
    2,475
    Likes Received:
    15
    Joined:
    Mar 12, 2003
    Location:
    Toronto,Canada
    I trying to replace a bad motor in a 78bj40 with a good motor from a 81 bj42.
    Will a 81 3b motor mount directly to a 78 bj40 transmission? If so, which year clutch, pressure plate, throw bearing and slave clutch cylinder would I use? Would any modifications be required?
    Thx Inadvance
     
  2. lowenbrau

    lowenbrau

    Messages:
    3,643
    Likes Received:
    65
    Joined:
    Jan 22, 2003
    Location:
    Calgary AB
    The tranny will bolt right up. Use the clutch, T/0 bearing etc from the '81

    The throttle body is different and will require some monkeying with the throttle cable. It might help to turn the 3b throttle body 90 degrees or swap the one off the B as long as it seems to be as big.

    I think there is something else but I can't think of it.
     
  3. mike

    mike 82bj42 1st project

    Messages:
    2,475
    Likes Received:
    15
    Joined:
    Mar 12, 2003
    Location:
    Toronto,Canada
    I should re-use the 81 clutch, 81 cover & pressure plate, 81 release bearing, and the 81 slave clutch cylinder. Everything should bolt right up and the clutch should function properly. Is there anything else I should be concerned about before I go ahead and swap the motors? Thx
     
  4. crushers

    crushers post ho

    Messages:
    22,189
    Likes Received:
    180
    Joined:
    Feb 10, 2004
    Location:
    Tara Ontario
    the exhaust manifolds are different so you will need to use the 3B manifold and a new exhaust is a good idea, i recommend a 2 1/2" aluminized with a quiet free flowing muffler.
     
  5. mike

    mike 82bj42 1st project

    Messages:
    2,475
    Likes Received:
    15
    Joined:
    Mar 12, 2003
    Location:
    Toronto,Canada
    Should I be concerned about the motor mounts positions? Thx
     
  6. crushers

    crushers post ho

    Messages:
    22,189
    Likes Received:
    180
    Joined:
    Feb 10, 2004
    Location:
    Tara Ontario
    if memory serves me right it is a straight bolt in...
     
  7. mike

    mike 82bj42 1st project

    Messages:
    2,475
    Likes Received:
    15
    Joined:
    Mar 12, 2003
    Location:
    Toronto,Canada
    Which bell housing and slave clutch cylinder should I use? Is there any difference between 81 and 77 parts? Thx
     
  8. lowenbrau

    lowenbrau

    Messages:
    3,643
    Likes Received:
    65
    Joined:
    Jan 22, 2003
    Location:
    Calgary AB
    Use all from one or all from the other. I'm pretty sure the parts are interchangeble anyway.
     
  9. crushers

    crushers post ho

    Messages:
    22,189
    Likes Received:
    180
    Joined:
    Feb 10, 2004
    Location:
    Tara Ontario
    as Bruce said, all of one or the other but i suggest going with the newer parts since you will probably be able to source parts longer...