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Late Nailhead transmissions


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Guest 40series
Is there a physical difference between the Dynaflow and the Super Turbine 400 ? The ST400 , would that be the forerunner to the Turbo Hydramatic 400 , if so are the bolt patterns the same ?

The 400 transmission is physically very different and appears as a Chevrolet 400 with the noticable difference of the bellhousing shape. The 64 Model was the ST400 and the 65-66 was the SP400 model. The later having the switch pitch convertor. It will bolt directly to your dynaflow equipped nailhead with and adapter bushing and flexplate. You will also need to use the 64-66 Starter or an aftermarket mini starter.

The bushing and flexplate can be found here:

buick nailhead 364 401 flexplate kit for SP400 trans : eBay Motors (item 260559874053 end time Mar-28-10 09:09:22 PDT)

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The SuperTurbine 400 was the same design as the GM THM400 used by all GM divisions, but with differences in the bellhousing patterns and the "Switch Pitch" torque converter (unique to Buick and Olds versions, requiring a switch pitch torque converter and the appropriate front pump assy., and electric throttle switches to do the kickdown at WOT functions and change the pitch inside of the torque converter). The "high angle" was used for idle and WOT (with a torque ratio of about 2.6) and "low angle" was used for cruising (with a torque ratio of about 2.0). Therefore, there was an "idle switch" and a "WOT" swith on the switch pitch versions, with only the "WOT" switch on the fixed-stator converter versions.

The SuperTurbine 300 was also a switch pitch transmission, but with two forward speeds.

Buick was the lead design division on the THM400. It is a premium design transmission, still having "life" in the form of the later 4L80 (THM400 w/OD) and 4L80E (electronic valve body controls) GMPowertrain transmission families.



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Now that you've been thoroughly confused, it's really pretty simple to tell what you'll be looking at. The ST400's (Buick's name for the TH400) will be a one piece unit. ST stands for Super Turbine. The name "turbine" has been associated with Buick transmissions for a long time. Dynaflows were called Twin Turbine and Triple Turbine transmissions.

Any Dynaflow will be a two piece unit having a bellhousing that's separate from the transmission. You can tell from what era a Dynaflow is by looking at the tailshaft to see if it was connected to a torque tube or an open drive shaft. All Dynaflows were similar to today's constant velocity transmissions where you never feel a shift. The L in a dynaflow was only to be used for getting out of sand, snow, or mud - or so the chassis manual says.

The ST400's (There never was anything called an SP400) all have a tag on the passengers side. It wll have the year and a BT, BS, or some other two letter designator on the side of the tag - that gives you an idea of what car it came from which would tell you something about the shift points built into the valve body and what gear ratio was in the rear end. The codes are both painted on and stamped in the tag.

The 64 ST400 and the 65/66 ST400's all had three forward drive speeds. In '64, the shifter had only D and L, but starting in drive ran you through all three gears. You can manually hold second gear in one of these by shifting from L to D, letting the trans shift into 2nd, then pulling the shift lever back to L. When you want the 3rd gear, you shift the lever to D and leave it there. Pulling the lever from D to L at any speed over 40 will engage the 2nd gear. As soon as the car speed reaches 40, it will automatically shift down to L.

Even with out a tag, you can tell the 64 ST400 from the 65/66 ST400 by looking at the number of terminals on the sending unit on the driver's side of the transmission. The 64 has only one termianl for the kickdown. The 65/66 will have two terminals, one for the kickdown and one for the solenoid that changes the pitch of the torque converter vanes.

Engine ID is just as simple. Beginning in '59, Buick used a one number / one letter system for engine ID. The first of the two will be either a 2 or a 4. 2 for two barrel , 4 for four barrel. The second of the two letters will be the production year. F=59, G=60, etc. Starting in 63, Buick used a two letter ID. The first letter was a year indicator J=63, K =64, etc, and the second was the engine indicator T=401 four barrel, W=425 four barrel, There were some two barrel engines, and some export engines (low compression) that had different letters. There are some other stamped numbers with this two letter code but they're not ID numbers, they have to do with production.

Here's a link to a complete listing.

Team Buick

Here's a link to show you where to look for the engine ID numbers.


Good luck and let us know what you find.


Edited by RivNut (see edit history)
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Just got back from having a look at the engine / trans. It's located under a dusty tarpaulin in a tight spot for identifying numbers etc.

This is what I was able to get off it.

Head casting number 1196914

Engine block casting number near distributor B1664705 10

Engine number was rusty and dusty and the best I could read was

5Y122292 ??

The engine has not been running for the best part of 15 -20 years maybe and has no carburettor or air cleaner, but does have distributor, power steering pump and alternator ( original ?? )

Any thoughts to year of manufacture ?

I'm trying to attach some photos, but they are too big so I'm trying to learn how.

Edited by Rooster (see edit history)
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