GM transmission help

[cob427sc]

I've had my 33 nearly done and have about 500 miles on the odometer. The drive train is a little out of the ordinary, but more importantly the car has a GM drivetrain and my first build with an automatic transmission. The specifics: 1958 Buick "nailhead" engine, 1964 Buick 400 auto transmission with stock torque converter. I know, and was warned about using the low rpm converter. The car drives fine except pulling up to a stop when you need both feet to stop or kick it into neutral. I want to replace the converter this winter but I'm not a GM guy and need to know if the T400 transmission and converter used in later GM cars is the same converter as mine? All kinds of converters for later chev/pontiac T400 but nobody lists anything for Buick. Probably going for a 2800-3000 stall speed. Any help appreciated.

[GoDadGo]

I'd call TCI or one of the other reputable transmission manufacturers/rebuilders.
My best guess is that they'd know for sure.
I love the idea of a nail head in a 33 HR.
Good Luck & Happy Stall Speeding!

Steve
https://www.youtube.com/channel/UC8m-MdRZvaH45Y6h4orIm7w/videos

[junglejim]

The turbo 350 & 400 converters will physically inter change, meaning that you can install in either trans. The stock type 400 converter is 13" in diameter, the 350 is 12". The only difference internally from any turbo 400 converter is some Buicks until 67 used a switch pitch or variable stator converter, which will not interchange with any other 400 converter without a pump change. I agree with Godadgo on consulting a reputable supplier & follow their recommendation, particularly because of the light weight of these cars.

[cob427sc]

Thanks for the info. My 64 tranny is the year before the 400 came with the switch pitch. I've been told that the switch pitch was used in the 65-67, then the bell housings were changed to match across the GM production line and would not bolt up to my 58 nailhead.

[JimLev]

I think 2800-3000 may still be a problem, especially at a cold fast idle.
With my LS3 and 4L65E tranny Tony recommended I use a converter from a 4L70 tranny.
The stock (4L65E) converter is 2400-2800 RPM, the one I bought (4L70) is 3000-3400.
It stops fine using one foot even at a fast idle when cold.

[cob427sc]

Jim, glad to hear your info. Most everyone I've spoken with has suggested the 2800-3000 range. This is one I kick myself about as I built a T-bucket a few years back with a 392 hemi and a stock dodge truck transmission and convertor (made my own adaptors). I had the same problem but with power brakes it was more manageable.

[JimLev]

I’m guessing (??) your nail head probably has more low end torque than my 376cu LS.

[cob427sc]

Nailheads are known for lots of low end torque and I agree with you that some of my problem comes from this problem. It's not terrible and more of an issue during warm up as I have a manual choke ( 3-dueces for carbs) and the idle is high (900-1000) until it warms up. After it warms up idle drops to about 600 and then its not so bad, but when I first fire up and back out of the garage I sometimes think I'm going to push the brake pedal through the floor.

[NAZ]

Contact ATI and ask about rebuilding your converter and adjust the stall speed. You can discuss the issue with them and they will advise you on what stall speed. Be prepared to give them your engine specs as stroke, torque, peak torque RPM, gearing all have an effect on stall speed. DO NOT shop around for a converter out of a catalog or online, stall speed is not an absolute value. You can't expect an advertised 3000 RPM stall converter to stall at 3000 RPM in a variety of cars, it doesn't work that way. I run a very loose converter and it stalls around 5000 RPM up here at 7000' ASL and 6000 RPM on a cool night in Phoenix where the engine is making considerably more torque in good air.