garage door opener safety reversal

Upgraded from a Craftsman 1/2 HP chain to a Chamberlain 1.25 HP belt drive. I used the old door bracket, header bracket, and ceiling bracket as is. I set the door closed position to fully closed right before the point where the rail starts to bow. When I do the safety reversal test, 2x4 flat under the garage door, it does not reverse. I have 2 questions:
1) The rail is parallel to the ceiling and I now know that it should have a bit of downward slope from the header to the motor, but how much? Is that really important and is that contributing to the failure of the safety reversal test?
2) The Chamberlain instructions for attaching the curved arm to the straight arm are fuzzy. "Bring arm sections together. Find two pairs of holes that line up and join sections." Problem is I can find more than two pairs of holes that line up so I opted for holes at the distant/bottom end of the straight arm. Is that important and is that contributing to the failure of the safety reversal test?

See attached images.

 

FYI this post indicates that I posted this "yesterday 10:10PM", perhaps the admins should check the time on their servers or whatever, I posted this about 5:10PM April 30, 2019 Central Daylight Time, Grand Forks, ND

 

You need to have at least 2 nuts and bolts engaged on the two piece of bracket coming from the opener to the door itself. If you travel a little more down the track, you can make this happen. If not, then the opener is positioned too high in relation to the door.

As far as the reverse sensors, the doors should reverse when a sensor if obstructed and the door should reverse when an object is encountered. I test not with a 2x4 but with my hand applying force about halfway through the doors closing.

 

Shorten the arm so it's more straight up and down, the front of the opener looks a bit high to me, but that could just be the picture? You can flip that header bracket up side down to lower it a bit. The belt looks loose, tighten it with door disconnected and no pressure on the trolley. The back looks ok, may be just a touch high, should be about 2 inches above the door. You may want to lube your springs they look dry.

 

Thanks Doorman2722! Appreciate it!

 

Thanks czizzi! The reverse sensors do work for obstructions.

I've heard the 2x4 test is crucial and is normally included in a home inspection. I'd like to get it right. It does reverse on a hand placed mid-travel.

as far as the door arm assembly, I will try to post a better picture - it is assembled with two bolts.

 

Here's hopefully a better pic of the join between curved arm and straight arm