I only have manual chain drive openers, on a 12'x12' and 15'4" x 12' tall overhead doors.

I choose to install, on both doors, these bumper springs, because I once pulled "too quickly" to lower one door (on chain drive's chain), and it loosen the door's cables, and they jumped off drum pulleys and I ruined both cables (had hardware store make new ones)

I learned, if you use the chain drive, to lower, it is best to go slow, BUT I put on new "pull-down ropes" and I first pull the the first door section (with rope), down to vertical, then use chain drive.

I ordered these overhead door "bumper springs", and this will assist "pushing the door from the horizontal position to vertical" {first few inches , or so} and it keeps those drum cables tight, right at the beginning, when you want the door to travel downward. I would want these "bumper springs" even with an electric jackshaft opener.

pictures:

(manual chain drive for shaft (full).jpg)

(overhead door bumper springs (full).jpg)

manual chain drive for shaft (full).jpg (54KB - 43 downloads)

overhead door bumper springs (full).jpg (42KB - 47 downloads)