CarKarDad the shelf is the reason I had to pony up for the liftmaster 3800's. They are jack shaft garage door openers and only rise 3" above the center of the shaft.
Which brings me to my current problem. I have only installed one so far but I have a problem with the tension monitor. When the door is raised and you push the button to close it the door cable goes slack for a split second as the door goes from stationary to starting to lower. This trips the tension monitor and the door won't close. For now I just put a screw underneath the tension monitor to keep it from closing completely when the cable is slack. What is the proper way to get around this? Any danger in my solution? I really don't see the point of the tension monitor if the cable breaks there is nothing the liftmaster can do to keep the door up.
Shop looks great.

I stumbled on this post and it kept nagging me, so you have made me stop lurking and make my first post on this forum.
The tension monitor is there to make sure there is always some tension on the cables so they don't jump out of their grooves on the drums where they wind around, not for a cable failure such as breakage or the end coming undone at the bottom roller. If one cable jumps the grooves on a drum the door will become crooked in the tracks and will very likely jamb as one side drops further than the other. In some cases when the cables jump at the end of the opening cycle, the door can continue its momentum and with the cables out of the drum groves can continue to roll horizontally out the top of the track.
The problem is that with your low headroom over the door and tight radius of the door tracks there is no weight really left on the cables with the door fully open. The lack of weight coupled with having electric, jackshaft openers, which start the closing cycle rather quickly leaves the cables slack as you say for a split second. Add a little bit of dust and grit to the insides of the horizontal section of track, or have a roller start to drag a little with age and the problem gets worse. While the doors may operate fine as you have them 99 times out of 100, there will be a time when they won't, and it will most likely occur when you have to be somewhere with no time to spare.
Sorry for the long wind, but the solution is simple and inexpensive. Get a set of pusher springs for each door, install and adjust them ASAP. They mount at the end of the horizontal tracks and the door tensions the springs during the last few inches of opening, the stored force of the springs gets the door started downward the instant the jackshaft starts moving. Once the springs are at the end of their travel gravity has enough pull to do the rest. Google "garage door pusher springs" for all the info you need.
Early one blustery morning this past winter the thermometer showed -32° C ( 24° below F ) I ran the tractor out of the heated shop to feed the cows. As my doors face north there was a fair bit of fresh snow piled against the outside of the door which fell in on the concrete floor when I opened the door. I usually leave the door open for under a minute to let some of the diesel smoke out of the shop and shovel any snow away from under the door seal or the seal will sometimes freeze to the floor. While shoveling the phone rang and I set the shovel aside to answer it, after the very brief call I hit the close button for the door and hopped on the tractor just in time to see the shovel leaning in the door jamb and the door come to a stop on top of the handle. It was enough for the cable to jump off the drum and make the 16 x 20 door immoveable. By the time I got the cable back on the drum, about an hour, the plumbing to the shop sink and toilet was frozen as was the brand new $3000.00 pressure washer. Luckily nothing split and everything was ok when it thawed. There are better times to have a door problem, but there is no "good" time to have a door stuck between open and closed.

I need tension monitors on my doors.