what trans should i use behind the 66 401.

Discussion in ''Da Nailhead' started by v8regalowner, Apr 14, 2011.

  1. v8regalowner

    v8regalowner Silver level contributor

    so ive been trying to read up and figure out exactly what trans i can use in the 66 gs behind the 401. i do believe it has the 2 speed st300 in it now from what i have read. so what can i put in without any kind of adapter plates and without having to modify how the shifter works too much. or am i better off just rebuilding whats in it. can i use either a 350, th400, sp400 or maybe an overdrive like the 200 4r or the 700r4. strickly a cruiser. i thought i read on here that the nailheads had a different bolt pattern then the normal b.o.p but i definatly could be wrong.
     
  2. John Codman

    John Codman Platinum Level Contributor

    If it is really stock, the transmission is a THM 400 Switch Pitch. That's about as good as you can do for a stocker. If you are a racer, The 700R4 or the electronic version of it are what you want. The four speeds have a lower first gear and absorb less horsepower.
     
  3. william.ali.kay

    william.ali.kay Needs more cowbell!

    You are correct in thinking that the Nailhead is not the same as BOP bolt pattern. Nothing will just bolt right up but a Nailhead specific tranny. Adaptors are made for just about any transmission now-a-days but I have never used them cause I cant afford them. So here is my .02.
    There are Th400's, St400's, and Sp400's with the Nailhead pattern. I THINK these will all "just bolt right up" but I am not 100% sure. A Nailhead master will soon chime in and verify or correct my info.:Smarty:
    Big cars from 1964, 1965, and 1966 would be a good place to start searching.
    I think there are some oddball exceptions that Ive read about, but I dont know about that stuff.
    Hope this helps.
     
  4. v8regalowner

    v8regalowner Silver level contributor

    To be honest with you I thought it should have the 400 but I put another post back when I got the car what trans should be in it and only 1 person responded and said st300. Guess I should just look at the pan. I'll leave it alone if that's what it is and just have it freshened up. Thanks as always guys u just made my day!
     
  5. v8regalowner

    v8regalowner Silver level contributor

    Well now im really confused. i just went out and looked at the car and the gear selector goes park r,n,d,l which i believe only makes it a 2 speed right? so i crawled underneat and the trans looks awfully small to be a sp400.
     
  6. nailheadnut

    nailheadnut Riviera addict

    ST (super turbine) 400 is Buick's name for the GM Corporate TH (turbo hydromatic) 400. Buick just likes to use the word Turbine in their transmissions. Has since the dynaflow era.

    SP400 is a nickname that someone - somewhere - sometime ago gave to the ST400's that came with the variable pitch (Switch Pitch) converter in '1965 and '1966. You'll never find a reference to a "SP400" in any Buick literature, only in these forums. It's used by the masses to differentiate it from the ST400's that don't have the variable pitch converter.

    The same ST400 was used in '67 but it now incorporated the BOP bell housing. The ST400's starting in '68 didn't have the "switch pitch" feature. (Accountants and costs:rant: )

    The '64 ST400 is a three speed ST400 but it does not have the "switch pitch" feature. In the cars, the shifter quadrant doesn't show the 2 for second gear.

    If your car is a 66 GS as in the Skylark line, the transmission is a two speed ST300 (it too has the switch pitch feature) If your car is a '66 Riviera Gran Sport, then it will have the ST400 w/ variable pitch converter but it will show a 2 in the shifter quadrant.

    All nailheads 364/401/425 have the same bell housing bolt pattern. The early models up through '63 (dynaflows) have a different crankshaft flange on them and you can't connect those engines to the ST400 transmission without an adapter even though they will physically bolt to the block. ALL ST400's will bolt to a 64 - 66 nailhead, but you'll need different switches, carburetors, linkages, and wiring to get them to operate properly.
     
  7. v8regalowner

    v8regalowner Silver level contributor

    Houston, it looks like i have my answer. So at this point im thinking about either trying to find all of the stuff to change it so the st400 or just rebuilding the st300 seeing that its a switch pitch. i would have to think i would have to alter the driveshaft and crossmember to put in the st400 also wouldnt i? seeing that im keeping the motor completly stock, other then doing docs dual plane i could keep the original trans and it should run fine as a cruiser i think. sorry i know im just rambling away but sometimes you just have to get your thoughts out there for others to comment on.
     
  8. nailheadnut

    nailheadnut Riviera addict

    The best way to make that conversion, if that's what you decide to do, would be to find a complete donor car and take EVERYTHING you need from it.

    Does your car have the console on the floor? If so, you'll need a floor shifter from a Riviera or Wildcat that came with a console so you'll have the correct number of detents in the shifter gate.

    If there's room under the floor pan for the ST400, you shouldn't have too much of a problem sliding the transmission cross member back (the GS does have a ladder frame rather than the big cars X frame doesn't it?) You'd then also need to fabricate a new drive shaft and get the correct "drive and driven" gears for the speedometer and cable.

    If I were just looking for a cruiser, I'd stick with making the ST300 work correctly. (I'm sticking with the dynaflow in my '63 Riviera. :)

    Ed
     
  9. sean Buick 76

    sean Buick 76 Buick Nut

    Find the ID tag on the trans. You can also find pics of the different pans so you can ID it. I would work with what you have rather than do a swap. Find out what you have, then buy a new converter from Jim W.

    The only reason I suggest adding a new conveter is because you could gain performance off the line with a good converter.
     
  10. nekkidhillbilly

    nekkidhillbilly jeffreyrigged youtube channel owner

    id go 200 -4r over 700r4 stronger lighter and less power to drive
     
  11. John Codman

    John Codman Platinum Level Contributor

    I F'd up. Sorry! I was of the impression that the GS was the same as the big Buicks. The ST 300 was the standard automatic tranny in the Skylark GS.
     
  12. gatkins2004

    gatkins2004 65spec401 frost bitten

    Can someone explain what this adapter would look like, part numbers or pictures even better.

    I picked up a 63 nailhead from a wildcat but want to use a ST400 that was on a 65 wildcat.

    Thanks a bunch,
    Gary
     
  13. CameoInvicta

    CameoInvicta Well-Known Member

    It's called a crank bushing adapter and looks like this:

    [​IMG]

    The purpose of the adapter is to decrese the ID of the crank flange, so it is the proper diameter to support the snout of the torque converter.

    You simply grind the raised area on the crank flange flush, and insert the adapter. I've done the swap and converted my '62 to a ST400.
     
  14. Bigpig455

    Bigpig455 Fastest of the slow....

    Dont be too quick to give up on the ST300 - mine performs well, and there are a couple mods that can be made to shift points and shift pressure that make it a contender. I know the first gear is pretty high and I dont know how long it will last doing strip duty, but i really dont mind it.
     
    mikethegoon likes this.
  15. brucer

    brucer Well-Known Member

    X2. I have a 65 GS with a 401 and the ST300. Properly set up it will pull like a freight train. Good off - the -line thanks to the switch pitch converter. And...awesome full throttle downshifts at highway speeds:TU:
     
  16. gatkins2004

    gatkins2004 65spec401 frost bitten

    Beautiful, thanks Andy!

    :beer
     
  17. nailheadnut

    nailheadnut Riviera addict

    Open this link to webrodder.com. It takes you through the complete swap from a dynaflow to an ST400, complete with pictures. They removed the OE bushing from the crank with a sawzall and then drove the new one in place. If you'd like more info on a complete rebuild of a nailhead then type nailhead in the search window. You'll find a complete overhaul as well as the installation of the St400.

    If you grind the OE hub off flush, there won't be any way to mount the new one.

    http://www.webrodder.com/article.php?AID=460&SID=21&CID=

    Ed
     
  18. 65GSConv4sp

    65GSConv4sp Well-Known Member

    Old thread, but I have a question regarding a 65 Skylark Gran Sport with the 401 and ST300. In the ST300, what are the drive and driven speedometer tooth counts with the standard 3.08 rear differential, as provided from the factory? And where can replacement speedometer gears be obtained for the ST300?
     
  19. 436'd Skylark

    436'd Skylark Sweet Fancy Moses!!!!!

    My 66 olds has an st300. Although in the olds world its a Jetaway 2 speed. Its a variable pitch converter. This is a full size car with a small block 330 and 2.78 gears. The car drives beautifully and is not doggy at all. Of course i know it would be better with a more modern transmission, but it works pretty well for what it is and I wouldn't replace it just for the sake of doing it.

    I'd suggest driving it with the ST300 and see what you think first.
     
  20. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    You might find that information in the 65 Chassis manual, probably not. Replacement DRIVEN gears are the same as 350 and 400 transmissions. It takes the same gear sleeves (2").

    Unless someone knows the tooth counts from individual experience, I think the best thing for you to do is to pull the DRIVEN gear sleeve out of your transmission, and count the number of teeth on your DRIVE gear. You can see the drive gear through the sleeve hole. With the transmission in neutral and the wheels off the ground, you can turn the drive shaft by hand and count the DRIVE teeth. The gear is helical, so it's a bit more difficult, but it is doable. You'll lose some fluid so get the back of the car as high as possible to minimize this.

    Once you know the DRIVE tooth count, all you need is rear tire size and gear ratio to figure out what DRIVEN gear you need.
     

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