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auto tranny swap

Discussion in '40- & 55-Series Tech' started by Jackson, Mar 26, 2003.

  1. Jackson

    Jackson

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    I've been doing a lot of reading, and it seems that the SM420 is a very popular tranny to swap into a Chevy V8 powered rig. If I'm going to do a tranny swap, I'd want to go with an auto tranny. Auto tranny info is harder to find - is there a preferred auto tranny to go with a Chevy 350? Any I should stay away from? And for the million dollar question - what kind of ball park number should I plan on spending to purchase the tranny and have it swapped in (assuming the 350 is already in the vehicle)?

    I did do a seach on the board first, and this is the info that I found - A Turbo 400 is a good auto, but can have some cooling issues. Autos are hard to do because of the lenght of the transmission. They are also very expensive to rig up. Tranny will run approx $500, but the adapter plate tranny/tcase can be as much as $750. Then there are misc other costs. The tcase will probably have to be relocated, and new drive shaft will probably have to be made.

    Does this sound right? Anything else I should know? Is it reasonable to hope the work could be done for no more than $2500?

    Thanks.
     
  2. Design311

    Design311

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    Here's a little bit of info that may help:

    http://www.off-road.com/jeep/tech/convtrans/gm/gmth350id.html
    http://www.off-road.com/jeep/tech/convtrans/gm/gmth400id.html

    For what it's worth, back in my hot-rod days I could pick up rebuilt TH350's for $299 plus core locally. I swapped a rebuilt unit in my 66 Chevy in high school and $299 was about the best price around. Might have to just call around your area and get some quotes. Or keep your eye out on Pirate4x4 or a local newspaper for a good used one. Hope that helps. Good luck!
     
  3. Jackson

    Jackson

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    Thanks for the info - I'll do some reading.

    It just occured to me - the Jeep Wrangler in a short wheelbased vehicle. Would an auto from a wrangler work? I'm sure those are very easy to find in junk yards and salvage shops.
     
  4. Jackson

    Jackson

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    OK, let me see if I've got this straight...

    TH350
    21 3/4"
    Advantages: relatively efficient
    Disadvantages: 3speed

    TH400 (replaced by 4L80E)
    24 1/2"
    Advantages: Stronger than TH350
    Disadvantages: 3speed, inefficient

    700R4 (replaced by 4L80E)
    23 1/2"
    Advantages: 4speed
    Disadvantages: relatively unreliable

    4L60E
    21 7/8"
    Advantages: 4speed, electronically controlled
    Disadvantages:

    4L80E
    26"
    Advantages: 4speed, electronically controlled
    Disadvantages:

    I would really prefer an OD since the rig will be seing a lot of highway.  It seems that GM corrected the problems with the tranny in 1987, so a rebult, post-'87 700R4 would be a good choice, right?  The 4L60E is the same tranny as the 700R4 except that it is electronically controlled?  Forgive my ignorance, but what advantages would an electroncially controlled tranny offer?  Advanced Adapters makes kits for all these transmissions.  I'm going to make some calls to see if I can get some estimates. Right now I think I'm leaning towards the 4L60E.
     
  5. PHAT MAX

    PHAT MAX

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    well if you lean the other way, i have a t-400 to three speed case adapter...with crossmember, driveshafts that fit, and a rebuilt three speed t-case attached. all for 500 bucks.

    -Max
     
  6. Jackson

    Jackson

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    Thanks for the offer - I'll let you know if I change my mind, but I'm pretty well set on a 3speed/overdrive tranny. The nearest trail is 110miles away.
     
  7. theo

    theo

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    A friend of mine has a 700R4. He has clearance issues between the tranny pan and the front driveshaft because the pan is so wide. He is going to have to have his custom driveshaft modified to get enough clearance.

    And his rear driveshaft is very short. It may give him problems if he decides to lift the truck. He may have been able to mount the engine farther forward; I wasn't around when he did that. But it has been over a year since he started and he still doesn't have 4WD. Also, he had to install a manual lockout to keep the thing from going in and out of overdrive at low speed. This doesn't seem like a big deal though.

    A computer controlled transmission requires a computer. Do you have TBI or TPI? If so I found some good info here: http://www.jagsthatrun.com/index.html

    If you like I can ask my friend how much he has spent so far. He has had someone else do most of the work, although I think he gets the brother-in-law rate for labor. Also, he may be a little embarassed about the cost. But $2500 sounds like a hell of a lot to me.
     
  8. Jackson

    Jackson

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    Good info, thanks. If you buddy is comfortable saying how much he's spent, I'd love to know. Is the engine/tranny basically complete?
     
  9. theo

    theo

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    I know he paid ~$900 for a complete, GM factory crate engine with Edelbrock Performer carb and manifold, Accel HEI, and 2 years left on the 3-year warranty. Don't know where he picked up the tranny but he had it rebuilt. He bought a nice console shift kit to go with it. I'll call him this evening and get back to you. :)
     
  10. Paul_A

    Paul_A

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    OK, guys, this is my first post to this list. I have been looking at it for a long time as well as SOR's and enjoyed the information very much. You're also pretty nice to eachother--a big plus over other lists I have been involved with.

    As to the auto tranny swap: I would look to a TH350. Once you get over the installation cost it is shorter, efficient, cooler to run, cheaper to run, easier to find parts, and replacements are only a wreck away. My '75 FJ40 is a SBC305 with a TH350, stock transfer case and Saginaw P/S. Drive shaft work and a trans cooler will have to be done no matter what auto you shovel under there. Sooo....that's my first two cents.
     
  11. theo

    theo

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    Jackson, I asked my friend about costs last night. He's not sure on some of it; He's a young fella and I think his dad picks up the tab and he works it off as he can. Also, he has an informal arrangement with his dad's friend the mechanic, so his labor costs are pretty low.

    The rebuilt 700R4 cost him $850. The AA adaptor was ~$650. He bought a B&M shifter for ~$200 but you could get by cheaper if you don't need the "slam shifter". Custom driveshafts were ~$400, but that includes new tubes and I think a longer slip yoke on the rear. (I paid $125 to have one of mine lengthened and the other shortened using the stock tubes and yokes.) He solved his front driveshaft clearance problem for the time being by bashing the transmission pan inwards. Otherwise he would have had to have a smaller diameter shaft made. He had to buy a longer speedometer cable and an oil cooler. Not sure about the bellhousing.

    Hope this helps some. :)

    Oh yeah, welcome to Mr. Swearingen's Neighborhood, Paul. It's a lovely day to talk Cruisers! You can thank Woody and his band of moderators for the quality of this forum.
     
  12. PHAT MAX

    PHAT MAX

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