Loose drive motor to gearbox fix-with pictures

As I plugged in my wire harness to one of the drive motors on my beam, I discovered it was loose to the gearbox. I’m assembling my frame at the time and I know it was tight when I installed it on my frame earlier. The only thing I could figure was vibration must have loosened something. So what else to do other than take it apart?!

Step 1: Loosen sprocket set screw with hex wrench (did not photograph this step) and remove sprocket.
Step 2: Loosen all 4 gearbox cover screws, them remove them. Place in safe place (magnetic fastener dish works great).


Step 3: Using a small jewelers screwdriver or similar tool, gently pry between the cover and the gearbox housing to separate and remove cover. NOTE: Be very slow, careful, and watch for any plastic bushings that might be stuck to the inside of the cover. Grease can sometimes cause parts to stick to them. I would recommend doing this over a clean rag laid out, and minimize how high you lift the cover before you flip it over. Inspect everything for loose or broken parts. If you are nervous about getting things back correctly, take a picture.


Step 4: In the picture above you will see a yellow arrow. Lift that gear off the shaft while holding down on the gear to the right of it. Again, grease can cause the two gears to stick together and if that happens parts can get lost if the separate while being moved.

Step 5: Lift the other set of gears out and place somewhere safe. Note that in the picture there is a plastic bushing on top of this gear. It may stay stuck on top of the gear or may fall off. Be sure to place these parts somewhere safe.


Step 6: Remove the worm gear, the small gear above it and the bushing (arrow pointing to it). Again, be careful not to loose anything. If you are concerned, take a photo first. NOTE: The worm gear has concave teeth which mesh with the “worm”. It may take a little gentle wiggle to get it to release from the worm. FUN FACT: The lone spiral gear is called a worm and the gear it drives is called the worm gear. Worm drives have advantages. First, they have very high speed reductions for a small size. Second, they can not free-wheel. This means they act like a natural brake and will only rotate when the worm is driven. Worms may be of a single start, 2 start, or more. To determine the number of “teeth” you look at the end and count how many “starts” you see. If you see 2 starts, then the ratio is 2: (however many teeth on the worm gear). Further math would need to be done with the rest of the compound gear train but this is the odd one.


Step 7: Tighten the 2 screws (below with yellow arrows).


Step 8: Assemble in reverse order. DO NOT FORCE anything. LOOK at the gears as you assemble them to insure they are meshing. You may need to rotate the gear you are installing a bit each way for them to slip together. Same thing with the cover. It should fit flush with the housing easily. Do not try to pull it tight with the screws. If it is not fitting, something is not meshing or a bushing is out of place. Install and tighten the 4 screws.



nice write up. add some red lock tite thread locker to they dont’ come loose again is my only suggestion. also might be possible to tighten the screws withonly taking out a few gears not all of them?

Unfortunately the right screw requires the last gear to be removed to access. Loctite is a good idea, i missed that.