There are few adjustments that can be made to the belt-driven garage door opener. Much like their chain driven counterparts, the adjustment mechanisms are on the trolley. Unlike their chain driven counterparts, you can only adjust the belt a couple of times before it absolutely needs replacing. Belts wear out over time and when they do, they stretch out of proportion. Although you can tighten the belt enough to operate the door, it is a good idea to consider replacing the belt.
Close the garage door using the garage door opener.
Place a step ladder under the rear of your garage door opener motor. Step on the ladder and unplug the garage door opener power cord from the ceiling electrical outlet. The opener uses a power cord much like any other home appliance.
Move the step ladder to where the belt connects to the trolley on the opener rail. The trolley is the portion that the garage door arm connects to the opener rail. The trolley consists of the inner trolley and the outer trolley. The inner trolley is where the drive belt attaches.
Locate the threaded shaft that the end of the drive belt connects to a piece of master link chain. The threaded shaft inserts through a stop plate on the trolley, with a screw spring securing it on the other side. Between the spring and the stop is a nut ring that attaches to the screw spring.
Push the threaded shaft toward the garage door with one hand and hand tighten the screw spring with your other hand. Turn the screw spring clockwise to press the spring against the trolley stop.
Release the threaded shaft and insert the tip of a flathead screwdriver between two of the screw spring coils near the trolley stop. Turn the head of the screw spring with a 7/16-inch wrench until you hear the spring pop the nut ring against the trolley stop.
Place the step ladder back under the motor and plug the opener power cord back into the ceiling outlet.