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Old 11-27-2019, 12:22 AM
1965gp 1965gp is offline
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Default 66 auto trans option

Did all 66 Automatic gto’s Get the ST300?

I haven’t looked to verify what is in the car, but figured since the engine is out it might make sense to have the Trans rebuilt.

If it has the ST300 is it worth rebuilding or should I switch to a 350/400?

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Old 11-27-2019, 12:40 AM
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Yes. All '64 thru '66 GTO's.

Most guys prefer a 3-speed auto. If you ever plan on big power, go with a correctly built TH400.

For bracket racing, I'd actually prefer a 2-speed. My trans guy said he can build up an ST-300 for bracket racing.

But, for street driving, a 3-speed will make the car feel more spunky.

Don't figure very many guys stay with the 2-speed, unless they are doing a numbers matching resto.


Last edited by ponyakr; 11-27-2019 at 12:48 AM.
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Old 11-27-2019, 07:49 AM
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As said above, the ST-300 was the only automatic installed in the '66 GTO. The TH-350 is a direct bolt in and even uses the same driveshaft. You'll have to tinker with shifter linkage and kick down cable, of course.
The first gear is so much lower than the two speed, it'll feel like you picked up 50 horsepower. Much recommended swap!

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Old 11-27-2019, 09:29 AM
66sprint6 66sprint6 is offline
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We switched to the TH350 in one day, it was so easy. What a difference off the line. Just had to add the kick down cable, which was simple. .

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Old 11-27-2019, 09:36 AM
1965gp 1965gp is offline
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Hmmm..... I have the TH 350 out of my 72 Firebird. Maybe it makes sense to have that rebuilt.

Would it be best to swap in a 67 shifter?

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Old 11-27-2019, 09:48 AM
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I installed a TH350 in my 68 Tempest & used the 2 speed column shifter w/no mods to it. If you have a floor shifter you may have to make some changes to it.

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Old 11-27-2019, 10:29 AM
Chief of the 60's Chief of the 60's is offline
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If you are going to modify it from stock you mind as well go with the 700R4 overdrive. The car will be much better on the open road and the lower RPMs at crusing speeds result in much less wear & tear on the engine.

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Old 11-27-2019, 05:10 PM
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If you have the 350, freshen it up and bolt it in. As others have said, it will entirely transform the car. You'll feel like it has another 50-100 horsepower. MUCH more responsive, and a bolt-in deal.

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Old 11-28-2019, 10:36 AM
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Quote:
Originally Posted by 1965gp View Post
Hmmm..... I have the TH 350 out of my 72 Firebird. Maybe it makes sense to have that rebuilt.

Would it be best to swap in a 67 shifter?
You can buy the kit to modify your 2 speed shifter from Shiftworks. The TH350 is the way to go if you already have the trans

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Old 11-28-2019, 12:13 PM
1965gp 1965gp is offline
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Thanks guys- I drove the Firebird with this Trans in it so I know it’s at least a good starting point. My neighbor works at a transmission shop so I can have him go through it.

Do I need to change the crossmember?

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Old 11-28-2019, 12:18 PM
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A couple of my friends did the 200R OD conversion.Tom

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Old 11-28-2019, 12:53 PM
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Quote:
Originally Posted by 1965gp View Post
Thanks guys- I drove the Firebird with this Trans in it so I know it’s at least a good starting point. My neighbor works at a transmission shop so I can have him go through it.

Do I need to change the crossmember?
Same crossmember in the same position, the TH350 swap from the ST300 couldn’t be easier.

You’re going to need a dipstick and tube that’s compatible if your current tube hits the firewall, which is likely. You’ll need to source a factory assembly from an A-body that was originally equipped with a TH350.

I’m about to swap a TH350 into my ‘64 Le Mans. I have a TH350 dipstick and tube from a ‘76 T/A that surely will interfere with the firewall after putting it in place to check. I sourced a good used ‘70 Tempest dipstick assembly that hugs the engine and trans much more closely, crossing my fingers that it will work when I get around to installing the engine and transmission.

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Old 11-28-2019, 02:24 PM
66sprint6 66sprint6 is offline
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You're right about that dipstick tube. I tried three of them before I got one that fit. I believe that it was an original from a '69 Chevelle.

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Old 12-27-2019, 11:07 PM
1965gp 1965gp is offline
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Well I had the shop pull the trans out and it looks like someone had already done the turbo 350 swap. That’s good cause I can have it built at my neighbors shop and everything should go right back in.

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Old 12-27-2019, 11:14 PM
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Nice, that was easy!

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