How do I replace a broken drive belt on an automatic door?

What Is Automatic Door Timing Belt?

An automatic door timing belt is a rubber belt that synchronizes the motor gearbox shaft with the moving door panels. The timing belt on an automatic door connects around a motor gearbox pulley on one end of the automatic door, to a return pulley or idler pulley on the opposite end of the automatic door. The moving door panels are connected to the timing belt by belt brackets. As the timing belt rotates from the motor gearbox running, the door panels move accordingly.

Function Of Automatic Door Timing Belt

The timing belt of an automatic door is a very important component. The timing belt itself is made up of teeth, which are small cogs on the belt. The teeth of the belt mesh with the grooves of the gearbox pulley and return pulley. If the timing belt is too loose and slips, the automatic door controller will not know the accurate position of the door panels. An example of this is if the automatic doors slam open. This can occur if the automatic door controller believes the doors are only opened half way when they are actually in the full open position.

Automatic Door Timing Belt Inspection and Preventative Maintenance

Always be sure the automatic door is turned off when doing any time of mechanical inspection. Never touch any moving parts!

Check Teeth On Belt
As part of good preventative maintenance, the automatic door timing belt should always be inspected. With the automatic door turned off, each belt tooth should be checked. Over time teeth can shear off of the belt or wear down. This can cause the timing belt to slip on the pulleys.



Check Tightness Of Belt
Another preventative maintenance check is to verify the overall tightness of the belt. With the door off, the timing belt should be loose with 1 or 2 inches of play up or down. If the belt is overtightened with little to no play, it will cause the motor to overwork and draw more amperage from the control system. This can wear down the motor and over heat the controller.

Check The Belt Brackets
Verify that all connecting belt brackets are tight. Over time the screws holding the belt clamps can loosen up. If the belt brackets do come loose during door operation they can hit the motor gearbox, rip through sensor wires, and damage the automatic door controller.


Verify Pulleys Are In Good Standing
Verify the motor gearbox pulley wheel is in good shape. If the pulley wheel is cracked or damaged, it can rip the timing belt. Do the same for the return pulley as well as check that the return pulley bearings are in good shape.

Common Signs Automatic Door Belt Needs To Be Replaced
Missing Teeth On Belt
If the automatic door timing belt is missing teeth, then it should be replaced.


Belt Is Cut or Severed
If the timing belt has snapped or is severed, a new timing belt should be installed.

Belt Is Loud and Squeaky
If the automatic door belt is loud and squeaks each time the door opens or closes, then it should be replaced. Many misconceptions is that the belt should be lubricated with oil or some alternative. Since the belt constantly rotates and travels right next to the electronic controller, electronic sensors, and various other electrical wires, lubricating the belt can result in that lubricant getting on the electrical components and shorting them out. Plus, the lubricant is a short term fix. Once the lubricant wears off of the belt in a matter of days, the belt will begin squeaking again. Also certain lubricants can damage or wear down the belt material over time.

How To Replace Automatic Door Timing Belt
Automatic door models vary with different looking belt brackets, motor gearbox pulleys, and return pulleys. However the overall concept of replacement is the same.

1. Determine Belt Type
If you know the automatic door make or model, then finding the replacement belt can be easy. Simply go to our automatic door parts page and click on the automatic door make, such as Stanley. Identify which Stanley belt matches the belt teeth you have. If you are unsure contact [email protected], and provide an image of your belt teeth. One of our experts can provide you a link to the correct belt kit.

2. Turn the automatic door off. Remove the existing belt from the automatic door. Lay the new belt next to it and cut it to the matching size.

3. The original belt will likely have drilled holes in it from belt bracket attachment. Be sure to match those holes.

4. Install new belt. Tightened the belt by moving the return pulley. The belt should have 1 to 2 inches of play up and down.

5. Attach belt brackets.

6. Turn automatic door on and verify the automatic door operates properly.

Cost Of Automatic Door Timing Belt Replacement - Do It Yourself
If you repair and replace the automatic door timing belt yourself you can be saving hundreds of dollars. Other than your own labor, automatic door timing belt can cost between $500 to $1400.

Automatic Door Timing Belt Replacement - Contractor or Technician
If you are contractor, handyman, or technician performing the service of replacing an automatic door timing belt, this can be a very profitable service call for you. Typically, an automatic door technician can make around $1200 to $2800 easily by replacing automatic door timing belt for a customer.

Technician Work Order
Travel Time
Timing Belt
Timing Belt Mark Up (Contractors Usually Charge 2x Of Their Cost)
Labor and Installation (Contractors Average 1 Hour Of Labor)