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Transmission swap

Discussion in 'The Hokey Ass Message Board' started by barnyardscraps, Dec 12, 2011.

  1. barnyardscraps
    Joined: Oct 17, 2011
    Posts: 6

    from Kansas

    I have a 1962 C20 with the 10 bolt rear end with 8 lug axles and had the muncie 318 3 speed. I'm wanting to swap to a muncie SM420 I believe out of a 64' casings are 3837334. Where it goes into the bell housing works perfect but what connects to the drive shaft is different. What needs to be done to the drive shaft to get it to work or would it be easier to find the right drive shaft for this transmission and will work with current rear end?

    1st picture is muncie 318 where it connects to drive shaft, second is sm420 where connects to drive shaft, 3rd is where drive shaft connects to rear end and fourth is where drive shaft goes into the muncie 318. Any help would be appreciated. Thanks,

    Attached Files:

  2. I believe that flange is for a double cardan joint like this one.

    It can be added to any drive shaft..

    Welcome and be sure to do an intro
  3. 56sedandelivery
    Joined: Nov 21, 2006
    Posts: 6,695

    Member Emeritus

    Actually, the granny low trans you have was designed to be used with a torque tube driveline,; you're going backwards in time. The "same" trans is made with an open driveline output shaft/extension housing, best to find one of those. Not a real popular trans, so it should'nt really cost too much. Why not go with a Saginaw 3 speed? OR, maybe find the MOPAR/New Process 3 speed with built in manual O.D. (and based on the MOPAR/New Process 4 speed, just re-geared differently)? Butch/56sedandelivery.

    OR, the trans you have had a parking brake on the extension housing, and another extension bolted to it also. It was designed for a driveline with a "built-in" slip yoke. I had an old Hydro once that came out of a big Chevrolet truck, had the parking brake on it, and I could'nt figure out a way to use it in one of my Sedan Deliveries as I did'nt have the "extra" extension housing for the U-joint, and would have had to have a slip yoke style driveline made. I'm sure there's no seal in the "extension" housing on the trans you have. Do you have the other parts for it? Butch/56sedandelivery.
    Last edited: Dec 12, 2011
  4. barnyardscraps
    Joined: Oct 17, 2011
    Posts: 6

    from Kansas

    Thanks for the input everyone, I did indeed find its not a 60's 4 speed but a 50's and that is the torque tube driveline. THe reason I was wanting to use it was it was free and I had it but now its for sale and I'm just contemplating rebuilding my original muncie 3 speed. I rebuilt the 235 straight six and a couple weeks later when in 3rd it'll just pop into neutral. Any suggestion on why it may be doing that? I figured its the syncros in the transmission. Thanks again all.

  5. high gear syncro rings, clips or too much end play or all of following, should be easy to find a 3 speed out of something else and get all syncro try newer stuff

    4 speed usually have a 2 piece driveshaft which can cause more problems on switchover
  6. squirrel
    Joined: Sep 23, 2004
    Posts: 49,859


    Jumping out of high gear in one of the old Muncie three speeds is often caused by a worn main drive gear, and or 2-3 shift drum. Wear on the sides of the splines is the problem.

    If you look around you might be able to find a few of those old 3 speeds to play with. They are mostly all the same, although they went to a shorter tail on later ones, and they also changed all the internal parts in the last year or two of production (65-66?) with a fine spline output shaft and differnt helical angles onthe gears. And the car transmissions don't have threads in the lower two mounting holes at the bellhousing, you'd need longer bolts and nuts to put a car trans in the truck.

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