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Technical Automatic in a 40 Ford

Discussion in 'Traditional Hot Rods' started by GonzoMN, Sep 22, 2020.

  1. GonzoMN
    Joined: Jun 16, 2007
    Posts: 416


    So, I tried searching, but maybe didn't use the right key words.
    I found a 40 ford I like. Built flathead, un-split bones, 39 Trans & 40 rear end.
    Like the car, but need an automatic.
    What is the best automatic & what all is involved in putting one in?
  2. what motor? flathead?, someone sells kits to bolt a c4 behind a flathead.
  3. alchemy
    Joined: Sep 27, 2002
    Posts: 15,869


    Lotsa cutting of the X member cradle, possible need to split the front wishbone if the trans hangs too low, either swap the 40 rearend for a latemodel or convert to open drive, and reconfigure the rear wishbones to locate this rearend since the torquetube is now gone. About an afternoon's worth of work.
  4. Petejoe
    Joined: Nov 27, 2002
    Posts: 10,585

    from Zoar, Ohio

    From the feedback I’ve read, Automatics turn just about all Flathead’s into dogs. Especially the heavier cars.
    Just an FYI.
    I’d consider an OHV engine if I was in your shoes. Good luck.
    Last edited: Sep 22, 2020

  5. 31Apickup
    Joined: Nov 8, 2005
    Posts: 2,319


    You need to remove the center of the x- member, the part is riveted in. It can be done on an assembled car. Replace with chassis engineering bolt in piece or fab your own, which they usually mount the split wishbones to.

    Sent from my iPhone using The H.A.M.B. mobile app
    Frank Carey, Hnstray and olscrounger like this.
  6. verde742
    Joined: Aug 11, 2010
    Posts: 5,405


    get a competent street rod shop to do it for you,
    you are in over yer head. JMO
    X38 and joel like this.
  7. Never thought too much about converting a flathead over to an automatic transmission. I'd think the C4 wouldn't have as much of the internal power losses that a lot of the larger transmissions might. And it seems like the driveability might be improved with a smaller, looser torque converter. Maybe like something from a 6 cylinder Falcon, Maverick or Mustang. And sharpening up your tune-up a bit wouldn't hurt either.
  8. Packrat
    Joined: Aug 25, 2005
    Posts: 446


    Can I ask, why do you need an automatic?
  9. 51504bat
    Joined: May 22, 2010
    Posts: 2,158


    The owner of the local muffler shop has a really nice '39 convertible that he put an automatic in cause he was having trouble shifting. You might give him a call and ask about what was involved. Don't know what kind response you'll get but he treated me right when he sold me the trans he removed. Still working fine in my '39 p/u. Anyway PM me if you want the shop number.
  10. 40FORDPU
    Joined: Mar 15, 2009
    Posts: 2,883

    from Yelm, Wa
    1. Northwest HAMBers

    If you go the route of an automatic, Gene at Flat-O-Matic (Oregon)will have what you need.
    jimmy six likes this.
  11. jnaki
    Joined: Jan 1, 2015
    Posts: 4,894



    After owning a 1940 Ford Sedan Delivery as my first car, the Flathead was not the most powerful motor around. The former owner had a big 348 motor in it and that was the version I wanted. But my pocket book settled for the 80 hp Flathead motor when I bought the sedan delivery. It met all of my needs for a cool teenager hot rod/surf transportation and having a different hot rod from all of the others rolling around in our high school cruising grounds or the multitude of beaches along the LB/LA /OC/SD shoreline.

    The Flathead was, IMHO, powerless to do what I wanted it to do in our road trips. Yes, it was very reliable and required a minimal amount of troubleshooting to keep it running well. But, the power…err…lack of power from the Flathead was not the most gracious thing. With two-three surfers, 2-3 longboards and all of the accessories for a pleasant beach day, the Flathead was just not strong enough to power through the almost weekly hill climb along PCH in North Laguna Beach, at El Morro Beach.

    (Check out the TV series Christina On The Coast… She drives up the same road 60 years later in her spiffy convertible…) The downhill was fun and we had to get it going at top speed in 3rd gear. But, the steep hill going South was just too much for the 3 speed Flathead horsepower. We had to down shift to 2nd and sometimes down to 1st to make it over the top.

    If we were to have an automatic, it would probably be so underpowered and slushy. We would still be in the slow lane, but just chugging up that slow, steep hill, hoping the motor would not blow up. If we had (you might have) more horsepower with the addition of a cam and possible larger bore, that would have given us more horsepower for an easy climb up the hill. Yours sounds like it is "built up," whatever that gets you...

    The problem was accentuated on the Conejo Hill climb, steep grade on the 101 Freeway from Camarillo up to the LA basin, normally shorter on miles and much faster… unless it was in our 40 Ford Sedan Delivery with the Flathead. We always took the flat Coastal Highway 1 route as we knew it would be a 1st gear climb on that several mile long hill climb into the LA BASIN on the way home.


    Ten years after high school, my wife and I purchased another red 1940 Ford Sedan Delivery with a 327 and automatic transmission. It had horsepower robbing A/C, but there was plenty of reserve horsepower in the SBC to easily climb up those steep grades on Coast Highway and the 101 Freeway in the Conejo Grade in Camarillo coming into the LA basin. Now, with the reserve SBC power and auto transmission, the long road trips were easily done, even with the automatic. More horsepower is not a laughing matter… it works for our old hot rods.

    Despite missing the shifting gear syndrome, it powered us to wherever we wanted to go. 250 miles to Santa Barbara? Not a problem… with the A/C on, that Conejo Grade was an inviting short cut home to Laguna Beach. But, we were coastal shoreline people and who doesn’t want to drive all along the beautiful part of the LA coast line with smiles on our faces?

    Closer Chainsmokers LA Coastline
  12. Hnstray
    Joined: Aug 23, 2009
    Posts: 11,585

    from Quincy, IL

    Great sense of humor you have there @Petejoe .......:D

    Petejoe likes this.
  13. Hnstray
    Joined: Aug 23, 2009
    Posts: 11,585

    from Quincy, IL

    Some years ago I swapped the closed drive trans of my ‘47 Ford for a ‘50 trans to convert to open drive line. Though I don’t have either a ‘50 Merc trans or a C-4 to measure, my guesstimate is they are close in length and equally important, similar in tail housing compactness.

    In my case, I drilled out the rivets in the bottom plate of the X and then removed the trans mount support from the X, replacing it with a piece I fabricated. Bolted the lower plate back into place. Probably very similar to what @31Apickup mentioned above.

    Granted, I did not have a trans pan to deal with, but that is far enough forward that I doubt it would be much of an issue.

    As for the questioner as to ‘why’......because that’s what he wants....why does it matter to anyone but the OP?

    Last edited: Sep 22, 2020
    GonzoMN likes this.
  14. Automotive Stud
    Joined: Sep 26, 2004
    Posts: 4,123

    Automotive Stud

    Sounds like a cool car. But I think you'd probably be better off buying a car that already has a small block/automatic in it. There's no shortage of decent street rods coming up for sale lately.
    olscrounger likes this.
  15. birdman1
    Joined: Dec 6, 2012
    Posts: 994


    The guy wants a automatic transmission. And you guys tell him not to do it. Why do you do that? He already decided what he wants.
    GonzoMN likes this.
  16. 73RR
    Joined: Jan 29, 2007
    Posts: 6,398


    ...apparently all of you youngns still have good working knees and such...:confused:

  17. sloppy jalopies
    Joined: Jun 29, 2015
    Posts: 4,187

    sloppy jalopies

    flathead's center of crankshaft is not centered in the bell/block bolt circle...
    careful if you buy a kit...
  18. 4tford
    Joined: Aug 27, 2005
    Posts: 1,677


    I have a automatic in my 40 but I have a hemi powering it. my trans is a turbo 400 but it has a short tail shaft that positions it centered on the crossmember. The question would be is what kind of HP and torque is your flathead putting out to make your 40 meet what your needs are for that combo? There should be data out there comparing in put power to drive the auto trans your looking at.
  19. TrailerTrashToo
    Joined: Jun 20, 2018
    Posts: 722


  20. 1971BB427
    Joined: Mar 6, 2010
    Posts: 5,884

    from Oregon

    Not really true. It depends on the automatic, and what 1st gear it has. A 700R4 has a super low 3.07:1 first gear, which is lower than most manual transmissions have, so it will actually make the flathead even better pulling from a dead stop.
    And they make adapters just to do this swap. Of course one needs to swap the rear axle to have an open driveline, but that's not a big deal to most hotrodders.
    The OD of the 700R4 will also make any flathead much better on the highway with it's 2000 rpm cruise at around 65-70 mph. Flatheads last longer with lower rpm cruising.
  21. Marty Strode
    Joined: Apr 28, 2011
    Posts: 5,151

    Marty Strode

  22. abe lugo
    Joined: Nov 8, 2002
    Posts: 2,261

    abe lugo

    Easiest and cheapest solution is to have a a friend that admires your car to drive you around in it. Then you have some else shifting it for you. You can tell them to go faster or slower. Or even tell them to pay for the gas.
    done with my drunken Friday night rant.
  23. fordcoupeguy
    Joined: Apr 26, 2014
    Posts: 130


    My bro and I have done several with SBC and turbo 350s. You have to cut out some of the x member center ,make a trans mount and drop the wishbone ball mount about an inch. I think we used short shaft trans and of course open driveshaft rear ends. We have done this for years and it works very well. If you have a few basic skills you can pull it off.
  24. 0NE BAD 51 MERC
    Joined: Nov 12, 2010
    Posts: 1,368

    0NE BAD 51 MERC

    I had a c4 in My 40 coupe back in 1997 . I was running a 53 Merc flathead and a 9 inch rear end. My drop axle a nd trans mount came from Chassis engineering and the and trans adapter came from Flat o matic. Everything fit and worked perfectly!
    dwollam likes this.
  25. Garpo
    Joined: Jul 16, 2016
    Posts: 204


    Flatattack in Australia do a nice kit that uses a Toyota auto. Has the advantage of 4 speeds with top overdrive.
    Use with a rear gear of about 4:1 will get off the line well and give a nice highway cruise at around 2500rpm.
    Use a pre computer trans ex Supra, Mk II etc. Has all the usual clearance problems, just requires a little thought.
    I have this set up in a 32 sedan with mild flathead and love it.
  26. Weedburner 40
    Joined: Jan 26, 2006
    Posts: 744

    Weedburner 40

    Garpo, just tried to Google flatattack and keep getting an error code. Do you have their website address?
  27. 19Fordy
    Joined: May 17, 2003
    Posts: 6,925


    Verde 742 is correct. You are performing major surgery made much more difficult if the body is on the car.
    Removing the X member is not easy and cannot be done by the average person in an afternoon's work.
    Go to car shows and talk to folks who have already done what you desire.
    It quickly gets expensive with a snowball of req'd changes.
    Do all your homework and make a detailed plan before you start cutting your car.
    You really don't need to actually remove the entire X member. Cut it out even with the edges of the frame rails, leaving the riveted pieces in place. Then fabricate and install the required replacement piece. A friend of mine did this on a 41 Ford. He did split the wishbones and installed an open driveline.

    If you can't do the work yourself, be very sure you use a competent builder with pertinent experience. You don't want someone "learning" on your car.

    TO start, read all the info. here:
    Last edited: Oct 25, 2020
  28. 73RR
    Joined: Jan 29, 2007
    Posts: 6,398


    I found this:
    BUT, no Toyota swap parts.
    Maybe someone down-under could check them out.

    Last edited: Oct 25, 2020
  29. Garpo
    Joined: Jul 16, 2016
    Posts: 204


    Re Flatattack / Toyota auto. Website is
    USA agent is listed as Reds headers;
    I purchased my kit a couple of years back, but Mike Davidson appears to still be in business.
  30. dwollam
    Joined: Oct 22, 2012
    Posts: 1,130


    The Toyota adapter is listed in products under 4 speed transmission adapter. (4 speed automatic)


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