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i have a 3 speed manual tranny in my 72 302, and am thinking about putting in a automatic 3speed with overdrive. what modifications are going to need to be made??
You're going to have to remove all the manual transmission stuff, and add automatic transmission stuff. :-) Tranny, bell housing, clutch, pressure plate, flywheel, pilot bushing in the crank, z-bar and associated linkage, and the first half of the driveshaft. Now replace with the flexplate, torque converter, flywheel, transmission, and an automatic tranny driveshaft - the front half anyway. You may or may not have to swap out or relocate the transmission cross member.Don't forget to run a vacuum line to the modulator valve, and plumb in a good tranny cooler. Heat will kill an auto transmission fast. Add a shifter and fill with fluid! It should take the better part of a case if the transmission was clear empty.
It depends on the kind of overdrive tranny you install. Some take computers and lock-up convertors. I think the early models may not. Can't say, dont own any...........and hope to NEVER do.
A good start would be a complete donor truck. You can take all the pieces that will make the conversion. That way you are not hunting down bits and pieces to try and make the thing work right.
The actual bolt in should be easy. The rear mount maybe need changed or moved. Nothing a drill can't remedy. A driveshaft may be needed also, or yours altered.
The early Aod did not have a computer and is a popular swap. They can be rebuilt to eliminate a couple inherent waeknesses but what I have read they reccomend not using the lockup convertor for any performance applications as it is weak. Getting the TVS cable adjusted properly is critical and so is having a proper shifter that the detents are indexed with the ones on the tranny. Your tranny won't live long if you don't get these things right. I have read some good articles in Hot Rod and Car Craft on these swaps so maybe you can find the back issues on their websites. They don't address the swap into a pickup but have a lot of good info.