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As reported previously, one of our first goals for my recently acquired '67 Lemans/GTO-clone project car was to swap the original ST300 2-speed transmission for an aod.

Between this forum and information pulled from SA Design's How To Restore Your GTO, we felt fairly confident we could make this happen. A local boneyard supplied the trans, sourced from a 1989 Cadillac. An Aamco Transmission shop quoted a very reasonable price to do the work - so my husband chose to turn it over to them rather than tackle it himself.

We actually got lucky with the Aamco shop in particular, because these guys are really into vintage muscle cars, including one tech who is a big GTO fan. They checked out the trans, found it to be in good shape, bolted it right in with no modifications necessary to the rear mount or driveshaft. Even the trans' dipstick tube fit right into place behind my car's later-model 400.

Summit Racing-supplied torque converter lock-up kit and kick-down cable kit completed the installation and we drove it home today. Works great. Little bit of an adjustment to the kick-down cable is in order, but all in all we're good to go. Trans cost $250, and Aamco charged $850 for the entire job. Factoring in cost of the Summit components, and considering improved drivability and fuel economy, it would seem to be a very good investment.
 

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You'll like this transmission. I'm. Just finishing up reinstalling mine after a high performance build by Extreme Automatics in North Carolina. The adjustment of the throttle valve cable is critical with this transmission. If its not right you'll smoke the clutches. I hope they installed the geometry correction bracket on your carb, its a necessity to get the proper arc for the full range of travel for the cable. At wide open throttle the cable needs to be fully extended, and at idle it needs to be adjusted so that there is a pressure increase as soon as the accelerator pedal is pressed. The best way to check is with a pressure gauge, there is a pressure port plug with 1/8 in pipe thread located on the drivers side above the shift linkage. You need about 6ft of hose and a 300 psi LIQUID FILLED gauge. If you google extreme automatics and click on 200 4R he explains how to do it.
 

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What Kilkm68 says, big time. This is not a 'close is good enough' tranny. Dialed in right on the money, it'll do just fine. A hair out of adjustment, and the clutches will go up un smoke in the blink of an eye. That said, Your first gear ratio just went from 1.76:1 to something like 2.75:1 and you now have overdrive. The car should accelerate like it has 100 more horsepower and will easily knock down excellent fuel mileage on the freeway. Overdrive is one of the best (if not THE best) mods you can do to one of these cars to bring them into the 21st century.
 

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Sounds like a pretty painless swap! Always nice to pick up a few mpg even if it's not a daily driver. Nice work! :beer:
 

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Interesting about the rear mount. I have a 200r waiting install in mine and while the overall length of the trans is the same the mount sits further back on the 200 trans than the original trans.
 

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That's a great swap. If my GTO wasn't numbers matching I would be doing that in a heartbeat.
Believe it or not JVM, my GTO is numbers matching too....It's just that the drivetrain is safely in storage and I have a different engine , trans and rear axle in the car now. Someday I may even go back to original. :eek:


All you would need to change is the trans and converter and no one else would know the difference. ;)
 

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...and when you do re-install the crossmember, make SURE that you check the driveline angles front and rear. If they're not right, you'll have a vibration in the drive shaft that will "feel" like it's a balance problem, but it won't be.

If they aren't dead on, the easiest correction is to install a set of adjustable UPPER rear control arms, then use them to correct the angles.

Bear
 
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