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Technical Questions about Muncie to TH350 swap.

Discussion in 'The Hokey Ass Message Board' started by Russco, May 8, 2017.

  1. Russco
    Joined: Nov 27, 2005
    Posts: 4,068

    Russco
    Member
    from Central IL

    I recently sold my Cometkazi truck to a friend of my wifes. She thought she would be OK with the 4 speed but now she wants me to swap it out for an automatic. So I have a few questions maybe you guys can help me with. I'm pretty sure it will use the same crossmember mounting location but, looking at store bought TH350's I see 2 options on the tail shaft length a 6'' and a 9" which one would be the same as the Muncie so I wouldnt have to change drive shaft length? It looks like Summit sells a TCI street fighter, they also sell a Performance Automatic brand for about the same price and I see B&M has one but Summit doesn't carry them. Does anyone have any experience with these ready to run 350's or have any recommendations? Its a mild blown 327 probably make 450 or so HP at the flywheel 2400 pound truck with a 342 gear. I figure I will need a flexplate, converter, trans, lokar shifter, dipstick, transcooler and lines and about 3 gallons of fluid. am I missing anything else?I'm kinda bummed she wants to do this but its hers now so its her call, I just think its way cooler with the Muncie, Thanks in advance Mike
     
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  2. I not positive but I kinda remember there are 3 tail shaft length for a TH350. You need the shortest one. And then there is a fine spline and course spline output shafts so you driveline might need a different yoke.
     
  3. 2OLD2FAST
    Joined: Feb 3, 2010
    Posts: 1,765

    2OLD2FAST
    Member
    from illinois

    Gee Honey , I can't find a good auto , Hey , do you know how expensive that'll be ? , I'll have to cut up the chassis to do that , I won't be able to hook up a speedo , We'll hav to buy a new radiator......Just a few I could come up with....Do you realize how much that'll de-value the truck ?
     
  4. I believe you are thinking of PGs . One spline...same as Muncie
     
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  5. Deadbird
    Joined: Jul 28, 2005
    Posts: 1,107

    Deadbird
    Member

    Well, that's a bummer. I don't have any good answers for you Mike. I usually chuck those automatics as quick as I can. I do remember ditching a powerglide in a 68 Camaro in favor of the Muncie. It bolted right in. Will you need to swap the radiator to run a trans cooler line?
     
  6. Deadbird
    Joined: Jul 28, 2005
    Posts: 1,107

    Deadbird
    Member

    Oh, and is there enough clearance in the floor or will you have to make the tunnel bigger?
     
  7. mgtstumpy
    Joined: Jul 20, 2006
    Posts: 7,613

    mgtstumpy
    Member

  8. Russco
    Joined: Nov 27, 2005
    Posts: 4,068

    Russco
    Member
    from Central IL

    I told her when she bought it I would switch it over if she didn't like or couldn't drive the 4 speed. I don't know what she did or how but her left ankle is all swolen after driving it to and from Torque Fest this weekend.
     
  9. chevy57dude
    Joined: Dec 10, 2007
    Posts: 5,025

    chevy57dude
    Member

    This doesn't answer the OP's specific question, but possibly info that can help. Just did the opposite swap in the OT '72 El. Removed the short tail 400TH and installed a Muncie. Same length,but the crossmember had to be flipped around so the pad reached forward. Also had to swap driveshaft yokes.
     
  10. Russco
    Joined: Nov 27, 2005
    Posts: 4,068

    Russco
    Member
    from Central IL

    Now I'm a bit confused. The chart above shows the Muncie total length to be 29.3" and the TH350 to be 27 5/8" (6"tailshaft) I thought there was one that was a direct swap, (same trans mount and driveshaft length) am I wrong about that? I have swapped a few autos to Muncies and don't remember having to have a driveshaft made but it's. even a long time maybe I'm remembering wrong?
     
  11. TudorJeff
    Joined: Feb 13, 2007
    Posts: 1,125

    TudorJeff
    Member

    All the direct swap transmissions are "slightly" different in lengths but the splines on the yoke are usually long enough to make up the difference. Same as when you lower or raise a vehicle and the splines stick out a little further or a little less. Since you are going about 1.5" shorter, you should not have any problems with the yoke sticking out further. If it does not engage into the transmission far enough to make you comfortable, you can get a longer yoke and just swap out that part, even can be trimmed to fit.

    Also these are the best 1-800 transmissions in my opinion.

    http://www.phoenixtrans.com/
     
  12. Kan Kustom
    Joined: Jul 20, 2009
    Posts: 2,314

    Kan Kustom
    Member

    I am with you. Pull a 4 speed ? Give her a sport utility and inform her she is not a hotrodder.
     
  13. Russco
    Joined: Nov 27, 2005
    Posts: 4,068

    Russco
    Member
    from Central IL

    I'll check them out Jeff Thanks
    Normally I'd agree with that, but after living through this horrible crash and then having her A coupe run off into a ditch on the interstate and break the front axle off. AND still want to not only get in one of these things, but drive a 2400 pound car with a blown small block Chevy, I'm not going to argue with her about her ankle not being able to push a cluth pedal down.
    . crash.jpg crash2.jpg
     
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  14. Kan Kustom
    Joined: Jul 20, 2009
    Posts: 2,314

    Kan Kustom
    Member

    I stand corrected. Open mouth, put in foot. How do I always manage to slap myself in the face ? :(
     
  15. twofosho
    Joined: Nov 10, 2005
    Posts: 1,153

    twofosho
    Member

    Ran into the similar thing with my sister's Camaro. Due to back issues, 4 speeds are out, and it's automatics only, so her Camaro has gone from PG to T350 to 200R4. The 200R4 has a 1st gear lower than a T350, a .6 OD/lock up converter, and most all are dual bolt pattern to fit Chev and B-O-P-C blocks. It's been a while, but I remember the mounting pad and driveline/yoke being the same for a short tail Muncie, PG, and T350.
    While the PG, T350 and 200R4 tail shaft length are fractions of an inch of each other, the pad location on the 200R4 is the same as a Camaro T400 and required changing the crossmember out for the stock T400 Camaro crossmember I had been hoarding. I might have had to use the T400 yoke too, but (to quote Hillary Clinton) I don't recall. Just don't forget, the 200R4 has a reputation of not being very strong stock and you'll probably want it to have it built up by someone reputable if you're going to put a lot of power (torque) through it, even if it's from a Monte SS or Buick turbo car. Supposedly can be made stronger than the 4R700, though.
     
  16. Russco
    Joined: Nov 27, 2005
    Posts: 4,068

    Russco
    Member
    from Central IL

    No, you're fine. I'm still trying to talk her out the auto myself. I'm going to try one last ditch effort and try to modify the pedals to make it easier before I concede myself. She's been known to answer to "Pussyfoot" because her legs are so short her feet smell like pussy....
     
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  17. Russco
    Joined: Nov 27, 2005
    Posts: 4,068

    Russco
    Member
    from Central IL

    I built the chassis from scratch and moving the crossmember rearward would be a giant pain. If I do put an Auto in it simply for ease of installation I'm going with a TH350. That's why I'm asking about a direct swap out. I want to be able to use same trans mounting and Drive shaft length.
     
  18. DDDenny
    Joined: Feb 6, 2015
    Posts: 12,335

    DDDenny
    Member
    from oregon

    Centerforce clutches are easier on the leg.
     
  19. Russco
    Joined: Nov 27, 2005
    Posts: 4,068

    Russco
    Member
    from Central IL


    While it's not a center force, it's not a heavy spring clutch, it's actually a fairly easy diaphragm pressure plate and Custom made 6 puck disc.
     
  20. ...she should leave it alone and buy another car,...then sell this one,...
    ...did her A get totalled?,...or will it be rebuilt?

    ...if you go with the auto, just mount a trans cooler on the framerail beside the trans, long as it's in an airflow it'll work just fine.
     
    Last edited: May 10, 2017
  21. Russco
    Joined: Nov 27, 2005
    Posts: 4,068

    Russco
    Member
    from Central IL

    I fixed her A Coupe but she was afraid of it after that so we sold it. She is dead set on driving the Cometkazi truck still
     
  22. gimpyshotrods
    Joined: May 20, 2009
    Posts: 16,244

    gimpyshotrods
    Member

    I pulled a TH350 out of my high school 1969 Malibu, and put in a M21. I do not recall moving the crossmember, and I did not change the drive shaft. I do not recall what the tail shaft length was, but if someone else has that detail, that is what works. The holes in the mount pad are slotted, so a bit of change can be accommodated. You might need to slot.

    Also, if I remember correctly, the mounting pad on the TH350 is on the main case, so that does not move, regardless of tailshaft length.
     
    Last edited: May 10, 2017
  23. gimpyshotrods
    Joined: May 20, 2009
    Posts: 16,244

    gimpyshotrods
    Member

    I want to say that it was the 6" tail housing, which I think makes sense.

    With a 6" tail, a TH350 is 27.625".

    A Muncie/Saginaw is 28.3", for a difference of 0.675".
     
  24. 56sedandelivery
    Joined: Nov 21, 2006
    Posts: 5,779

    56sedandelivery
    ALLIANCE MEMBER

    Short shaft TH350 (6 inch extension housing) will bolt right into/onto your existing crossmember transmission mount, and the speedometer cable should be the correct length. Takes the SAME slip-yoke. As long as you use a flexplate the same diameter of your current flywheel, you can even use/keep the existing starter motor.
    I am Butch/56sedandelivery.
     
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  25. Moriarity
    Joined: Apr 11, 2001
    Posts: 15,195

    Moriarity
    SUPER MODERATOR
    Staff Member

    I just did the reverse of this swap in my off topic 66 chevelle. short turbo 350 to a muncie 4 speed. It could not have been easier. same crossmember and driveshaft. everything fit perfect
     
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  26. Russco
    Joined: Nov 27, 2005
    Posts: 4,068

    Russco
    Member
    from Central IL

    Thanks fellas! That's what I was hoping for. My driveshaft now is pretty close so as long as the TH250 is the same or even a little shorter I should be golden. I still hate to do it to the truck but it's hers now. I'm still going to do a pedal extension on all 3 and hope that will help make it easier for her and she'll change her mind about the automatic. Maybe even install a line lock for her to help on hills?
     
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  27. continentaljohn
    Joined: Jul 24, 2002
    Posts: 4,194

    continentaljohn
    Member

    You know if you put in a automatic with a reverse Manuel valve body and a nice stall you can have a bunch of fun.
    Mike Have you tried a hydrolic throw out and centerforce diapham clutch. I had to change mine over in the 68 bronco for my wife. It helps but in stop and go traffic no stick is fun .
     
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  28. 56sedandelivery
    Joined: Nov 21, 2006
    Posts: 5,779

    56sedandelivery
    ALLIANCE MEMBER

    Your last post Russco, you said TH250; are you now going with a TH250, or is that a typo? TH250 will fit the same as a TH350, but is weaker. Just so you're aware. I am Butch./56sedandelivery.
     
  29. Russco
    Joined: Nov 27, 2005
    Posts: 4,068

    Russco
    Member
    from Central IL

    Yes it should read TH350
     
  30. Mr48chev
    Joined: Dec 28, 2007
    Posts: 25,619

    Mr48chev
    ALLIANCE MEMBER

    I full and well realize that some of the previous posters think that it is a total sacrilege to change from a 4 speed to an automatic but my left knee keeps telling me that it is getting damned tired of pushing clutch pedals. I'm still planning on 5 speeds for both the 48 and the model A but that may change if I have to have my knee replaced.
     
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