C3 3 Speed Automatic Good or Bad?
Race Director
Joined: Nov 2006
Posts: 13,256
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From: Sunshine Coast, Queensland, Australia
2025 C3 of the Year Finalist - Modified
2024 C3 of the Year Finalist- Modified
2022 C3 of the Year Finalist - Modified
Cruise-In VIII Veteran
I am not a huge fan of any Automatic transmission.
as for beginner track training. Wouldn't consider an Auto of any kind, but that's just me. Is the old 3 speed auto tough enough? I would really think so. If all the computer control's are still working properly on this 81. Could be fun.
Me, I'd still look for a manual car.
you Drive a Manual, you ride in an Auto.
as for beginner track training. Wouldn't consider an Auto of any kind, but that's just me. Is the old 3 speed auto tough enough? I would really think so. If all the computer control's are still working properly on this 81. Could be fun.
Me, I'd still look for a manual car.
you Drive a Manual, you ride in an Auto.
Last edited by 4-vettes; Sep 5, 2020 at 03:01 AM.
Race Director
Joined: Mar 2017
Posts: 11,953
Likes: 4,510
From: Virginia
The aluminum Dana differential is more likely to be the weak link in the 80 through 82 cars. Save your pennies, and do an iron differential conversion (with the batwing) when the differential breaks. Duntov does this, and @GTR1999 has also recommended this to me, so I'm casually looking for an Eaton differential.
https://www.duntovmotors.com/differentials-80-82.php
Save your nickels and dimes to add a third pedal to that car.
https://www.duntovmotors.com/differentials-80-82.php
Save your nickels and dimes to add a third pedal to that car.
Racer
Joined: Nov 2017
Posts: 319
Likes: 125
From: Midwest
From '78-'81, the only automatic transmission the factory installed in Corvettes was the Turbo Hydra-Matic 350. It's a good, solid and reasonably tough transmission.
It should hold up as long as you still run the stock '81 190hp 350 in the car, and you're not getting serious about running it long and hard. Make sure the fluid and filter are clean.
From '68-'77, the factory mated the Turbo Hydra-Matic 400 (also a 3-speed) to high performance big and small block engines. That transmission was a more rugged, heavy-duty automatic that could withstand more punishment.
It should hold up as long as you still run the stock '81 190hp 350 in the car, and you're not getting serious about running it long and hard. Make sure the fluid and filter are clean.
From '68-'77, the factory mated the Turbo Hydra-Matic 400 (also a 3-speed) to high performance big and small block engines. That transmission was a more rugged, heavy-duty automatic that could withstand more punishment.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
That vintage of THM-350 was not designed to handle copious amounts of torque. It would probably do well up to 150% of the engine torque available from factory engines (which were paired with the THM-350). You can have your transmission rebuilt with stronger parts, if needed; or you could exchange it for a sturdier unit...or a well-built overdrive automatic.
Racer
Joined: Oct 2001
Posts: 474
Likes: 64
From: Portage La Prairie Manitoba
If you put a good transmission cooler on it , shift kit, and service it ...........its good for 375 hp
Rear diff is fine too...... unless you intend to put slicks on the car and drag race.... the stock driveline is fine
