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Convert '81 C3 from manual to automatic

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Old Aug 21, 2024 | 12:00 PM
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Default Convert '81 C3 from manual to automatic

Is this possible? I am considering this as it would increase the "cruising" factor and hopefully lower RPMs while on the highway. Thanks!
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Old Aug 21, 2024 | 12:07 PM
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Yes it’s possible, people have done it before.

Although you seem to be going the other direction. Most people want to swap from an automatic to a manual. Personally I understand the desire to want an automatic for the get in and go convenience, and not loathing traffic. Doesn’t make it any less “fun” to drive, although I’m sure you’ll get people in this thread that disagree.

Keep in mind a turbo 350 or 400 has the same 1:1 final gear, so without overdrive your highway RPMs will be the same.

If you’re not too keen on keeping your actual car but want one without a stick, you might want to find someone with an automatic and do a swap with them.

If you’re set on keeping your own car then a 200-4R or 700-R4 would work nicely. I’m sure many parts from a 1982 would fit without modifications.
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Old Aug 21, 2024 | 12:17 PM
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Thanks for the quick reply @Piersonpie !

I am looking for one with an overdrive indeed. So that would be the 200-4R or 700R4 then? I am keen on keeping my own car. Have done lots of work to it and finalizing it at the moment for a repaint as the last step.

How much work would be involved for this swap in manhours if I want to get this done by a Corvette specialist?
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Old Aug 21, 2024 | 12:17 PM
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Silver Sport, SST has a great kit,
Some one will say it's a few pennies cheaper to do it on your own, but in the end it's not much different price wise, Their tech support is fantastic,

https://www.shiftsst.com/why-buy-fro...SACEgI1_fD_BwE
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Old Aug 21, 2024 | 12:45 PM
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I would look at the 200-4R. It has a smaller change in ratios between first and second gear making it a smoother transition while accelerating.

Not that it affects you in your situation, but it’s also the same length as a turbo 350, making swapping between the two much easier.

I can’t comment on the length of time since I haven’t done it myself (yet), but it shouldn’t be too long. Something you need to be concerned about is a throttle valve cable, think of it as a mechanical version of a throttle position sensor. It needs to be properly calibrated to prevent overheating and other transmission failures. I might be wrong, but I think your Edelbrock 1406 carb has a bracket on the throttle linkage for attaching the cable.
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Old Aug 21, 2024 | 04:56 PM
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aalmans
Yeah. It's doable. I did it with a 200-4R.
I think the 81 has a goofball crossmember that you'd want to replace anyway.
here you go. lotsa info
https://www.corvetteforum.com/forums...late-c3-3.html



Originally Posted by aalmans
Is this possible? I am considering this as it would increase the "cruising" factor and hopefully lower RPMs while on the highway. Thanks!
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Old Aug 24, 2024 | 01:07 PM
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Seen that you are in The Netherlands, like me (hoi!), then be aware that the 200R4 is very hard to find here.
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Old Aug 24, 2024 | 01:47 PM
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Originally Posted by worship79
Seen that you are in The Netherlands, like me (hoi!), then be aware that the 200R4 is very hard to find here.
I figured as much. Any idea where I could try?
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Old Aug 24, 2024 | 02:11 PM
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Originally Posted by aalmans
I figured as much. Any idea where I could try?
Look for an 80s Monti Carlo ss an 80s olds 442 of a Buick regal. They used the 2004r theres also a Caddy that used them in the 80s but I cant remember which model.
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Old Aug 24, 2024 | 02:21 PM
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Old Aug 24, 2024 | 04:06 PM
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aalmans,

You will need some type of ATF cooler out front. Your manual trans radiator likely does not have the provision for cooling.

It would be easy enough to run rubber lines to a remote cooler. You don't need anything huge, just efficient.
There is room in front of radiator for a 8 x 11 inch cooler, 1 & 1/2" thick.
If you have A/C the condenser will limit a remote cooler to 3/4" think. When the hood is fully open the tip of the hood will be really close to the trans cooler.

Most ATF cooler kits come with ample special rubber hose lines, clamps and mounting hardware.
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Old Aug 25, 2024 | 04:51 AM
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Thanks all for the responses! I fear that these other cars are even harder to find over here. Let me check with a local Corvette specialist to see if they can source one together with the additional cooler as mentioned...
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Old Aug 25, 2024 | 06:00 AM
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Personally I really can't understand destroying a car like this!
Makes absolutely no sense whatsoever to completely suck all the fun out of this sports car!
Not to mention devalue it!
There are so many out there with automatics they wish they didn't get stuck with. And then to even consider this!
Truly sad.
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Old Aug 25, 2024 | 09:35 AM
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Originally Posted by aalmans
Thanks all for the responses! I fear that these other cars are even harder to find over here. Let me check with a local Corvette specialist to see if they can source one together with the additional cooler as mentioned...
Maybe Amazon in Europe carries some remote coolers. B&M makes a nice unit.
I have a thin one in series with the radiator cooler. You won't have that option with your Rad.

Just don't go too small of BTU, because heat destroys trannys more than abuse.
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Old Aug 25, 2024 | 09:40 AM
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Originally Posted by 4-vettes
Personally I really can't understand destroying a car like this!
Makes absolutely no sense whatsoever to completely suck all the fun out of this sports car!
Not to mention devalue it!
There are so many out there with automatics they wish they didn't get stuck with. And then to even consider this!
Truly sad.
As mentioned before, and you still don't get it, not everyone wants to shove a third pedal.
Ever heard of bad knees, bad ankles, handicapped, disabled?

There are tens of thousands of buyers out there that would prefer autos.
And I didn't "get stuck with" an auto. It's what I wanted.
Filter your rude remarks.
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Old Aug 25, 2024 | 10:42 AM
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aalmans
The cooler is no big deal. I used 2 coolers. 1 down behind the license plate and the other, short & wide, in front of the a/c condenser (so the hood can open without touching it). I'll see if I can find some pictures. I used braided SS hose and easily routed it.

I found 1 picture. The larger cooler down low came with my tranny but if I placed it against the a/c condenser then the hood would hit it when opened, so I bought a short wide cooler and plumbed them in series. The one against the a/c condenser gets air drawn by the rad fan. I had a temp gauge on the tranny pan for at least 6 months and it always stayed cool.





Originally Posted by HeadsU.P.
Maybe Amazon in Europe carries some remote coolers. B&M makes a nice unit.
I have a thin one in series with the radiator cooler. You won't have that option with your Rad.

Just don't go too small of BTU, because heat destroys trannys more than abuse.

Last edited by carriljc; Aug 25, 2024 at 11:12 AM.
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Old Sep 2, 2024 | 03:24 AM
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Default 700r4

I'd almost suggest a swap, because I have a manual conversion on my bucket list, haha! Definitely interested in your manual parts, so feel free to DM me when you get around to selling them.

I'd go for a 700R4 or a more modern automatic. Having the driveshaft modified or finding a fitting one is not that hard here. If my manual plan fails, a modern automatic with overdrive is definitely the next option.
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Old Sep 2, 2024 | 03:28 AM
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Originally Posted by worship79
I'd almost suggest a swap, because I have a manual conversion on my bucket list, haha! Definitely interested in your manual parts, so feel free to DM me when you get around to selling them.

I'd go for a 700R4 or a more modern automatic. Having the driveshaft modified or finding a fitting one is not that hard here. If my manual plan fails, a modern automatic with overdrive is definitely the next option.
What type of transmission do you have then? A swap would be an option.
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Old Sep 2, 2024 | 07:10 AM
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Last year for a manual 4-speed Corvette, ever.
Resale value is going to take a hit, manuals still sell for more.
Why not just swap diff gears?

Leave that Super T-10 right where it is!
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Old Sep 2, 2024 | 07:47 AM
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Originally Posted by L88Plus
Last year for a manual 4-speed Corvette, ever.
Resale value is going to take a hit, manuals still sell for more.
Why not just swap diff gears?

Leave that Super T-10 right where it is!
That is another option indeed. I do not mind the manual so much but highway RPMs are driving me nuts. It is about 2800 RPM at 60MPH.

According to the previous owner it has 3.73 rear gears. Would changing gears change RPMs that much? According to a local Corvette specialist it would only shave off about 300 RPM? I also would not mind less torque. It has enough.
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