Going to flush the trans cooler lines on my 81 F100,is the top line the return line, or is it the bottom one?

Second question is: I have been offered the use of a friend's garage to finish up what I have to do, before getting it to drive. Right now it has no fluid in the transmission, can I safely pull it behind his truck, (not on a trailer) for the short 2 mile distance, or should I put some fluid in the pan first?

 

I don't think it makes any difference what line is what as I would disconnect them from the trany to do the flushing.
This way you are flushing the lines & cooler and nothing will get pushed into the trany.

As for towing, it sounds like the trany might have been rebuilt but no ATF pumped thru it yet?
If that is the case or it has been drained and sitting that way for a bit I would drop the drive shaft for the tow.
The reason is with out any ATF pumped thru it for a bit things can be dry and now they would be spinning with out any lube.
That can hurt things and you would be rebuilding it again.
Just drop the drive shaft to be safe!
Dave ----

 

Thanks for the info. The aerosol can of trans flush I bought just said to disconnect the feed line, I assume from the radiator end. Trans was in very good working condition , my friend who gave me the truck had it wrapped in shrink wrap when it was pulled 3 years ago, drained it before we put it in

 

I know it could be a pain but I would remove both lines at the trany then to do the flushing.
Dave ----

 

x2

Here's a good video on DIY transmission flushing.
\