dean wrote:
My few-months-old Sears 3/4HP garage door opener, lifts a double door
up nice and smooth. However, when it goes down again, its like the
motor is instantly up to speed and the door knocks its way down for a
few seconds, jolting everything hard.

As far as I know there are two adjusters that determine where the
upmost and downmost points are, but I am not sure if there is any way
to adjust the descent start. Put in a spring between the arm and the
door?

Thanks for any tips!

DeanB

Your spring(s) need to be adjusted. The door is binding because of
unequal tension.