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Technical Thinking about putting a later model automatic with OD behind my 1966 318 poly

Discussion in 'The Hokey Ass Message Board' started by Bart Kolodziejczak, Dec 12, 2019.

  1. So as I understand it, my 66 poly would be a 318a engine. I currently have a 4 speed behind it (original I think) with a granny low and a 3:91 rear end. Where I live, freeway speeds are 75 and most people run 80 or more. This truck as currently configured cannot reach those speeds, that is why I am looking at an automatic with overdrive option. Has anyone done this conversion before and have a list or parts and instructions available? I am looking at using an a518 46RH trans, but I cannot get a clear answer as to whether or not this would bolt up behind the 318 poly.

    Any information and/or guidance would be much appreciated!
     
  2. alphabet soup
    Joined: Jan 8, 2011
    Posts: 2,019

    alphabet soup
    ALLIANCE MEMBER

    Anything that fits a LA style 318 will fit the poly. They use the same everything even the crankshaft.
     
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  3. squirrel
    Joined: Sep 23, 2004
    Posts: 55,637

    squirrel
    Member

    How about swapping in some 3.23 rear gears? I expect it would be less hassle/expense.
     
  4. Thanks for the info alphabet soup!
     

  5. I have considered this, but it is unclear if the amount of RPM change would get me to the speeds I am trying to reach. Then there is the concern of retaining the ability to take off in second gear. I used an online calculator and figured going from 3:91 to 2:93 would buy me 600 RPM
     
  6. squirrel
    Joined: Sep 23, 2004
    Posts: 55,637

    squirrel
    Member

    It might surprise you, how happy the engine will be turning the RPM that is required to go at highway speeds, with 3.23 gears. It works. That's how most cars were built in the 1960s. Trucks got steeper gears, because they generally didn't need to get driven so fast, and they had to haul loads. Now that you're using your truck more like a car than a truck, you can use the car gearing, instead of the truck gearing.

    But if you can figure out how to get an overdrive in there and working without too much fuss, that would be great. Fortunately your engine is new enough that it should mate up with the modern transmissions.
     
  7. Part of the reason to go to the automatic was so my wife would drive the truck, but if it becomes too much cost and effort to find and install an automatic with OD, I may just take your suggestion Jim! I am open to all options!
     
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  8. squirrel
    Joined: Sep 23, 2004
    Posts: 55,637

    squirrel
    Member

    I expect there are several other reasons that your wife will find to not drive the truck even if it has an automatic, but what do I know, I've been married, and had an old truck, for 36 years next week.
     
    Bart Kolodziejczak likes this.
  9. Congrats on 36 years! That is quite an accomplishment these days! I have been married 27 years, but it took me 3 wives to get here ;-) My wife does drive my 69 Coronet 4 door with an automatic, and she wants to drive the 69 Corvette with a 427 and 4 speed, I really do not want her to do that. She also says she wants to drive the truck, and I believe her, so I am investigating the options of the automatic with OD and will report back to her what it would take in terms of cost and see how she feels. Hopefully this will keep her mind off of driving the Corvette! ;-)
     
  10. squirrel
    Joined: Sep 23, 2004
    Posts: 55,637

    squirrel
    Member

    Thanks!

    My wife was driving a Dart with manual 3 speed when I met her...so she doesn't have any trouble driving the manual equipped cars/trucks. But she bought a new truck 20 years ago, and has mostly been driving newer stuff ever since.

    I'm starting to get that way, myself. But I still like taking road trips in old cars, and get my old truck out every now and then (I'll be hauling stuff to the dump with it today). It's been a long time since she drove it.
     
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  11. mkubacak
    Joined: Jun 20, 2005
    Posts: 200

    mkubacak
    Member

    This calculator allows you to make side by side comparisons of changes.

    http://www.grimmjeeper.com/gears.html

    Good god man don't put an auto in it. This world does not need any more vehicles with automatic transmissions.
     
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  12. THIS!
     
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  13. daliant
    Joined: Nov 25, 2009
    Posts: 689

    daliant
    Member

    The problem with putting a newer automatic behind a poly engine is the hub on the back of the crank is too small for the more modern ('68 and newer) torque converter. The bellhousing bolt pattern is the same for the poly and later small blocks however.
    It would be easier to put a more highway friendly rear gear in it to keep up with todays traffic.
     
    Last edited: Dec 12, 2019
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  14. 73RR
    Joined: Jan 29, 2007
    Posts: 7,145

    73RR
    Member

    Most days I am afflicted with CRS but IIRC, the small hub issue was a 273 problem not a 318 problem.
    The 65 318 on my stand has 'normal' dimensions.

    To the OP, be sure to check out this web site if you stay with the later trans. https://transmissioncenter.net/product-category/dodge/727/?product-tag=conversion-kits

    .
     
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  15. squirrel
    Joined: Sep 23, 2004
    Posts: 55,637

    squirrel
    Member

    I think the converter pilot size change was made in the early-mid 60s, but I can't remember what year exactly. I suppose we could look it up. I did get bit by that on a slant 6 many years ago.
     
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  16. yep....check that block build date and the crank - early Poly cranks are different than the last years of poly 318 production........
     
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  17. derbydad276
    Joined: May 29, 2011
    Posts: 1,336

    derbydad276
    Member

  18. I know very little about MOPAR, patterns, but a close friend of mine adapted a 518 tranny to a 392 Hemi. This adapter, as well as being a plate, also has an adapter for the crankshaft. If it will be helpful, I have a couple of pictures of this adapter that I can post.

    You have my sympathy, in my Cameo, I changed out my M21 for a TH400 in 1975 to please my wife, and regularly wish that I would have at least kept the 4 speed. ( I did find a super T10, so now I at least have the option)
    My situation is slightly different than yours, in that with the TH400, I am using a separate planetary OD, and although I originally ran 4.56 gears, but am now happy running a 3.73 gearset.
    Bob
     
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  19. The 318 Poly block from 1957 to 1967 will bolt both the cast iron and alloy torqueflites to it, however pre 1962 use 8 studs from the converter forward thru the crank flange and do not use a flexplate..........1962 to 1966/67 318 Polys use a flexplate and 6 bolts and are the same setup AFAIK as the LA series 318 wedge........therefore...... the alloy T/F cannot be used on the pre 1962 engines without either using the same adaptor that early Chrysler Hemis use or swapping to the later crank in the pre 62 block...........andyd
     
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  20. greybeard360
    Joined: Feb 28, 2008
    Posts: 2,072

    greybeard360
    Member

    Why not just bolt in a A833 o/d trans? Can be bought cheap enough.
     
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  21. 392
    Joined: Feb 27, 2007
    Posts: 1,206

    392
    Member

    I have a 46rh behind my 392 And couldn’t be happier. Your 318 pattern etc is the same as the 92. I used a Wilcap adaptor. What I did on mine since it is a 1995 and was a lock up 3 prong electrical connection type Transmission was to change input shaft to accept a non lock up converter. With doing that you eliminate the lock up but still have the overdrive. I know others will say there is nothing wrong with the lock up but with that modification you can get a wider band of converter and enjoy od. No other parts needed for controlling the lock up. If you find the 90-91 they were just od with 2 prong connector. Also look up getting better fluid flow to the rear od. Google It’s been awhile and forgot exactly what I did.
     
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  22. earlymopar
    Joined: Feb 26, 2007
    Posts: 1,608

    earlymopar
    Member

    The bell housing bolt pattern on the Poly 318 (A series) is not identical to the later 318 (LA series). The poly is symmetrical in the locations shown below. The LA is not. Later bell housings and transmissions can be mounted to the poly but there is one bolt that can't be used since it doesn't align.

    - EM


    Poly Pattern.GIF
     
  23. This is a picture of the 518 to 392 adapter.
    Bob 518_392_adapt_sm-p.jpg
     
  24. Arominus
    Joined: Feb 2, 2011
    Posts: 394

    Arominus
    Member

    Yes it will bolt on since its a 66. 62-66 use the modern small block flange, 55-61 poly's need to use the early hemi style adapter for 62+ small block torqueflights. I grabbed my 3 wire 518 out of a 2wd 93 ram van w/ a 318, which is ideal as the stock torque converter is setup for internal balancing. If you grab a 518 off a 360, the converter will be wrong for your 318. I would stick with the lockup converter, especially for highway use, its worth some rpm at speed and improves fuel mileage and reduces the amount of heat the trans produces at speed.

    You can automate lockup and OD using Vac switches or, if you want to be sneaky hi tech HGM makes a controller box (compu shift mini) for the 518 that uses a speed sensor and a throttle position sensor that will automate OD/lockup as well. You can also just run 2 toggle switches and wire them to the 3 wire connector to manually lock up and hit OD. If you only want OD to be on when you're highway cruising that can work, though i do recommend automating it for ease of use.
     
    Last edited: Dec 13, 2019
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  25. squirrel
    Joined: Sep 23, 2004
    Posts: 55,637

    squirrel
    Member

    So....was the back of the 318 the same on all Poly engines, and changed in 67 when they went to the Wedge (LA) design?

    or did it change somewhere along the way?

    Seems there are two conflicting stories presented here. And I don't know the answer.
     
  26. Arominus
    Joined: Feb 2, 2011
    Posts: 394

    Arominus
    Member

    It changed in 62 when the aluminum torqueflight came out with the integrated bellhousing. This is also when Chrysler changed from the 8 bolt flange to the 6 bolt. All of the earlier poly's (chrysler/dodge/plymouth) are the same as the early hemi and have to use an adapter. The 62-66 318 poly is the only poly that can bolt on 904's/A500's and 727's/A518's without an adapter.
     
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  27. squirrel
    Joined: Sep 23, 2004
    Posts: 55,637

    squirrel
    Member

    Thanks for the clarification. That's what I thought...
     
  28. 73RR
    Joined: Jan 29, 2007
    Posts: 7,145

    73RR
    Member

    Arominus is spot on! Oh, thanks for saving me the trouble of alot of typing!!

    .
     

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