TH400 Question
Thread Starter
Racer
Joined: Aug 2018
Posts: 252
Likes: 48
From: Cincinnati, Ohio
TH400 Question
New Vette owner – 1975 with I think TH400 Trans because the shifter has overdrive. Motor and trans missing of course . Wanting to keep it stock, so no 700/200 swap. Question when looking for a trans, what should I be looking for – Years, Length, Tail shaft, Yoke Ect
Note: The yoke and drive shaft still intact.
Thank, Mike
Note: The yoke and drive shaft still intact.
Thank, Mike
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From: San Antonio, TX/Mahopac, NY
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A TH400 is a three speed automatic transmission used behind most big block GM engines, but it is not an overdrive.
Thread Starter
Racer
Joined: Aug 2018
Posts: 252
Likes: 48
From: Cincinnati, Ohio
OK, Thanks. So let me ask this - I bought the car from a guy that is friends of friends buddy - Whoooo. I have the title! So he knows nothing about the car so i am trying to figure out what i have. Brand new console with shiftier and shift indicator plate and it has 1st,2nd,3rd and o for overdrive. So i assumed Chevy made a overdrive trans for that year. Now after doing a bunch of reading im guessing it had a 400r trans in it? I see that they make a overdrive kit for the Vette. So it could be possible. - Am i thinking right or wayyyyyyy off.
Thank, Mike
Thank, Mike
Race Director
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From: North of Toronto - Ontario
Chev didn't make an overdrive until around 81 or 82. Someone may have changed your car and installed a 200r or 700r but it left the factory with a TH400
M
82 all had overdrive, not sure if 81 had it as an option or not
M
M
82 all had overdrive, not sure if 81 had it as an option or not
M
Last edited by Mooser; Aug 16, 2018 at 04:20 PM.
Race Director
Joined: Jul 2018
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From: San Antonio, TX/Mahopac, NY
2024 Corvette of the Year Finalist - Modified
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2023 C7 of the Year Winner - Modified
The TH400 was the only automatic available that year. Frankly, it is heavy and a bit of a torque hog (meaning less torque to the rear wheels). Since your car is not original and you have to find a new drive train anyway, why not go with an overdrive tranny? I have a 700R4 in my 1961 and I like it, but it does have a bit of a sharp shift between 1st and 2nd given the wide ratio between those gears. 2004R trannies are pretty stout and might be a better solution for you. What engine and how much HP/TQ are you thinking?
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Race Director
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From: North of Toronto - Ontario
I would also suggest the 200R
You said you have the trans yoke still on the driveshaft, You could measure the diameter of the shaft just behind the yoke to see if you can tell what trans might have been in there (200r4 or 700r are the two most common swaps if it was an overdrive as your console shows)
M
You said you have the trans yoke still on the driveshaft, You could measure the diameter of the shaft just behind the yoke to see if you can tell what trans might have been in there (200r4 or 700r are the two most common swaps if it was an overdrive as your console shows)
M
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Melting Slicks
Joined: Oct 2010
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From: "ɹǝpunuʍop", Adelaide, South Australia
remove center console and see if an aftermarket "shiftworks" detent horseshoe and "decal" is fitted.
https://shiftworks.com/collections/c...=3303151239189
https://shiftworks.com/collections/c...=3303151239189
Le Mans Master
Joined: Sep 2013
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From: near the thumb in the mitten
Turbo 400 700r4 and 200-4r all are about the same length. The 400 has a larger 32 spline output shaft. The thm 350, 700r4 and 200-4r and all 4 speeds except the super T10 second design uses a smaller 27? Spline output shaft. The transmission pan is the easiest way to identify what you have. It's possible someone swapped in a o/d trans and shifter assembly from a 81-82.