I am going to have my 1986 El Camino Auto transmission rebuilt. It is a three speed. I would like to change the third gear to an overdrive to get better gas mileage. Is this possible?
Adding an overdrive to a three speed transmission, I don't think so. But I would ask a local speed shop or your transmission shop to see if there is an aftermarket overdrive kit that might be able to be added on.
What you need to find out is if an overdrive transmission can bolt up to your engine.
I sure some modifications will have to be made for this to be a successful repair.