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Thread: 425 & Th400

  1. #1
    Join Date
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    Default 425 & Th400

    I should know the answer to this, but will a modern TH400 bolt to a '66 425? Or is an adaptor kit required?

  2. #2
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    Default Re: 425 & Th400

    What do you mean by "modern"?

    You need a TH 400/Super Turbine 400 that has the nailhead "round-top" bellhousing. And (I think) those were all done in '66.

    No doubt there is an adapter kit that will allow you to bolt a BOP- or Chevy-style bellhousing to the Nailhead bolt pattern--but--I don't know where to get one.

    GM built transmissions for a bunch of cars you wouldn't ordinarily expect--Jaguars, Ferrari, Rolls-Royce/Bentley, etc. Might be that one of those cases is the same as a nailhead, but I wouldn't hold my breath.

    I know where there's a '64 TH 400 for Buick; and there's certainly other, newer, round-case 400s in the same salvage yard. Shipping is a bugger; and this yard isn't cheap.

  3. #3
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    Default Re: 425 & Th400

    Google for Bredtsen's (I think he also uses the name "Transmission Adaptors" or something like that). They make adaptors for pretty much everything Buick.

    Dan

    Quote Originally Posted by Lee Martin View Post
    I should know the answer to this, but will a modern TH400 bolt to a '66 425? Or is an adaptor kit required?

  4. #4
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    Default Re: 425 & Th400

    The transmission in the '64 is a ST400, but it DOES NOT have the switch pitch feature. Only the 65 -66 ST400 for nailheads, and the '67 with the BOP bellhousing are the s/p designs. If you can find a '66 LeSebre 340 engine with the ST400, it will have the s/p feature. However, most '66 LeSebres came with the ST300. The easiest way to tell is to pull the electric wire going to the terminal on the driver's side of the transmission: two terminal ends - switch pitch , one terminal end, just the kickdown for the passing gear .

    Ed
    The Nailhead Nut

    '63 Riviera - Original black w/ white leather
    '64 Riviera - Tastefully tweaked
    '93 Riviera - Saphire Blue Metallic w/ white leather

  5. #5
    Join Date
    Sep 2007
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    Default Re: 425 & Th400

    Thanks guys. I'm familiar with Bendsten's and will give him a call. What I'm trying to do is mate a Chevy pattern TCI TH400 to a '66 425. Sounds like I need the adaptor kit.

  6. #6
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    Default Re: 425 & Th400

    eelco has adapters and there about 300 bucks cheaper than benstends

    if you plan to go that route i would go all out and mount a od auto to it though
    66 skylark 2 dr hartop...... in progression
    83 lesabre 4 door waiting on its 350 buick
    04 sivlerado ccsb 4x4 2500 hd d max white
    12 kia sorento sx
    99 f150
    89 dodge spirit
    http://smg.photobucket.com/albums/v237/nekkidhillbilly/

  7. #7
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    Default Re: 425 & Th400

    Quote Originally Posted by nekkidhillbilly View Post
    eelco has adapters and there about 300 bucks cheaper than benstends

    if you plan to go that route i would go all out and mount a od auto to it though
    Thanks, but I'll stick with Bendsten's. I've dealt with EELCO before and wasn't that impressed. In fact, the manual adaptor kit they sold me for my other nailhead had the ring gear on the wrong side of the flywheel.

    As for an overdrive, the 425 is going into a '55 gasser.....for nostalgia sake, I want to use 1:1 for high gear.

  8. #8
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    Default Re: 425 & Th400

    Quote Originally Posted by Lee Martin View Post
    Thanks, but I'll stick with Bendsten's. I've dealt with EELCO before and wasn't that impressed..
    Google Marty Lackner, owner of Eelco, and see what pops up.

  9. #9
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    Default Re: 425 & Th400

    Quote Originally Posted by nailheadnut View Post
    Google Marty Lackner, owner of Eelco, and see what pops up.
    I know what pops up. That's why I'm going to go with Bendsten's.

    Thanks,
    -Lee

  10. #10
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    Default Re: 425 & Th400

    Quote Originally Posted by Lee Martin View Post
    I know what pops up. That's why I'm going to go with Bendsten's.

    Thanks,
    -Lee
    i bought from him no issues but to each there own

    but question what is the nostalgia reason for going to a 1:1 drive ratio? i dont see what would be different other than better mpg?
    66 skylark 2 dr hartop...... in progression
    83 lesabre 4 door waiting on its 350 buick
    04 sivlerado ccsb 4x4 2500 hd d max white
    12 kia sorento sx
    99 f150
    89 dodge spirit
    http://smg.photobucket.com/albums/v237/nekkidhillbilly/

  11. #11
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    Default Re: 425 & Th400

    Funny/strange , but both of these adapter guys have certain 'issues'. I might be missing something, but why not just bolt up a '65-6 ST400? -they're strong, cheap and available-shipping could be bad. I have some-I think Ed does-pick up in Mpls or Kansas City-where be you?
    Dan
    mostly Buicks-Pontiacs

  12. #12
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    Default Re: 425 & Th400

    Quote Originally Posted by lapham3@aol.com View Post
    Funny/strange , but both of these adapter guys have certain 'issues'. I might be missing something, but why not just bolt up a '65-6 ST400? -they're strong, cheap and available-shipping could be bad. I have some-I think Ed does-pick up in Mpls or Kansas City-where be you?
    i agree unless you want a od trans
    66 skylark 2 dr hartop...... in progression
    83 lesabre 4 door waiting on its 350 buick
    04 sivlerado ccsb 4x4 2500 hd d max white
    12 kia sorento sx
    99 f150
    89 dodge spirit
    http://smg.photobucket.com/albums/v237/nekkidhillbilly/

  13. #13
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    Default Re: 425 & Th400

    a Variable Pitch TH400 is an awsome tranny- it's like having 2 trans in 1. Hi stall for when you want to kick butt low stall for when you want to cruise. Both of my cars will be getting them. The Riv will be real soon!
    Anthony " Tony Yac" Yacopino
    BPG NE GS-GN

    1964 Riviera - Sold
    1966 Skylark 425 Nailhead, 4 speed, 3.73 posi. 2 miles of welding wire used thus far ;o)
    1968 GMC C25 307 2bbl. Sold
    1970 Skylark 350, 4 speed, 3.73 rear. Pro Touring- Stock Appearing. Project Jessica Rabbit. . . Traded

  14. #14
    Join Date
    Sep 2007
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    Default Re: 425 & Th400

    Thanks guys. I agree the ST400 is a nice unit. The thing is I have a line on a new TCI TH400 (GM pattern). The '55 is pretty much going to be a drag car, so I'm not worried about OD and mpg.

  15. #15
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    Default Re: 425 & Th400

    Quote Originally Posted by Lee Martin View Post
    The '55 is pretty much going to be a drag car, so I'm not worried about OD and mpg.
    You'll want a well-built fixed pitch converter for consistency, then.

    Devon
    Fuel & Brake Systems Engineer
    "I can live with doubt and uncertainty and not knowing. I think it's much more interesting to live not knowing than to have answers which might be wrong." - Feynman
    "Good data is precious. The problem I have is when some damned fool fails to use it properly." - Slingerland

  16. #16
    Mr62Buick Guest

    Default Re: 425 & Th400

    I have 2 1965 turbo 400's and one 1966 variable pitch trans. One of each is rebuilt and ready for install. These are the round bellhousing style that require no adapters at all to fit the nailhead as these are from nailheads.

  17. #17
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    Default Re: 425 & Th400

    If the two '65 ST400 are indeed what you say, then you have three variable pitch transmissions. Only the '64 was the non-varible pitch ST400 that came with a round (nailhead) bellhousing. Look at the terminals on the driver's side; if there are two, it is a variable pitch. If not, look at the tag on the passenger's side and look for the year and trans model - BT, BS, etc. - for proper identification.

    Ed
    The Nailhead Nut

    '63 Riviera - Original black w/ white leather
    '64 Riviera - Tastefully tweaked
    '93 Riviera - Saphire Blue Metallic w/ white leather

 

 

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