Well, I had suspected that plastic nut had something to do with it, but it took a good deal of searching to find this.

Before you get all set on finding that 3/4" wrench, grab the 11/16" while you are at it. My wrench set in the garage only went up to 11/16", so tracked to a 3/4" in the house, only to discover it was too big! :-P 11/16" worked.

On Monday, December 7, 2009 7:56:59 AM UTC-6, Ben Jammin wrote:
I recently replaced the springs on my garage door.

Now I need to adjust the closing force on my Genie GXL9900-2 1/2 hp
Screw Drive Garage Door Opener. Although the door opens and closes
freely and clearly by hand, it closes nearly all the way but then
reverses and goes back up when using "Genie". Yes, the safety light
beam is clear and properly adjusted.

On the GXL9900-2 you apparently adjust the opening and closing force by
turning either a nylon nut with a wrench or a metal screw rod with a
screwdriver slot on the back of the unit, unlike the electronic opening
and closing adjusters inside the white plastic "light lens" on newer
units.

I need to know if the nylon nut or the metal screw rod adjust the
closing force and which direction I turn the adjuster, clockwise or
couterclockwise, to increase the force.

I've tried to make the adjustment but it's just too difficult given two
adjustors and two different directions, plus climbing up and down a
ladder to hit the door control button. Got to be a better way!

The PDF manual on the Genie website is for the newer, all electronic
screw drive opener, not the older mechanical opener.

Any help would be most appreciated.

--ben