I am looking at a '66 in which the seller switched the transmission from an automatic to a standard. He put the automatic on a dry workbench where it has sat for 20 years. What should be done to make sure it will be OK to put back in? How can I or a mechanic tell if it is OK?

Thanks

 

You could look in side in the valve body and at the gears to see for rust or corrosion and turn the shaft to see if it'll turn and engage the gears without binding. If it had trans fluid left in it then it may be ok but I wouldn't recommend just running as is though. I had an engine that sat for 5 years with oil in it up to the heads and once it was emptied and refilled it turned right over.

 

The seals might be dried out. I would just get a rebuild kit and replace the seals and clutches. If it is a C4 or C6 they are simple to take a part. Kit with clutches and seals is $50-$100.

 

I have basic mechanical skills. How hard is it to rebuild it? It is a stock '66 automatic so I don't know if it is C$ or C6. Any tricky procedures or special tools? How hard is it to pull the standard transmission and put this back in?

 

they are easy to rebuild. Not many special tools, just snap ring pliers. I clutch spring compressor will make it easier, but you can use a couple of C clamps.
Swapping the transmissions won't be hard. You will need the floor shifter and linkage and transmission cooler lines. If he kept all that, it will be simple.

 

Yeah like JC said. Going from manual to auto is way easier and less time consuming but you will need all those parts. I've never rebuilt a trans but would probably have it professionally done the first time if it were to be put in a car that was to be used a lot as opposed to here and there.