Why Your Craftsman Belt Keeps Coming Off or Breaking


It gets frustrating when you have to keep stopping because your belt keeps falling off your mower. Your mower doesn’t quite work without it. Depending on the belt that fell off, your mower may not move or your deck stops working because the blades no longer spin. Finding the problem and fixing it will keep you moving and back to the things you enjoy doing.

Your Craftsman mower belt may come off if the belt has been stretched or shredded; the belt keepers and brackets have been bent, the spindles, pulleys or tensioner spring are damaged; or debris has been lodged in your deck.

I’ll go through the steps to troubleshoot the reasons your Craftsman belt may be falling off. Hopefully, after going through these steps, you’ll have a good working mower again.

Reasons your craftsman mower belt keeps coming off or breaking

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9 Reasons Why Your Craftsman Mower Belt Keeps Coming Off or Breaking

Craftsman Belt Keeper is Damaged

Your model Craftsman lawn mower may use a small rod-shaped post that sits next to the pulley. These are known as belt keepers. They are used to help guide the belt to keep it in place. The belt keepers can move out of place or become bent when a belt has a lot of slack in it or the belt snaps.

When there is extra slack in your Craftsman belt, the belt can hit and bend the belt keeper allowing the belt to jump off of the pulley. The belt keeper should sit very close to your belt, but it actually shouldn’t be touching it. You can use a small hammer or vice grip to adjust the belt keepers so they sit 1/8” to 1/4″ away from the pulley.

Loose Craftsman Mower Belt

Grab a hold of your belt to check if it seems loose. A belt becomes loose because it is worn or stretched from normal use. When this happens, you must replace the belt.

Shredded Craftsman Belt

When trying to find the reason your Craftsman mower belt keeps coming off, you may notice your belt has shredded marks on it. This is most likely from the belt running against a bracket or your belt keepers. You’ll need to check the route of your belt to see what it might be rubbing against.

You may notice a shiny spot on the metal of a bracket from wearing. This is a good indication your belt is rubbing on the bracket. Once you find the area that is causing the belt to shred, adjust the keeper or bracket correctly so the belt won’t continue to rub.

While you are checking the brackets, check the bushing in your idler bracket to ensure it is in good working order. Once your brackets and keepers are in their correct positions, replace the shredded belt with a new Craftsman belt.

Damaged Bearings in Pulleys or Spindle Housings on Your Craftsman Mower

If your belt, brackets and belt keepers are not the problem, you’ll want to look at your pulleys next. If the pulleys are not flat and rotating straight, a bearing in the pulley can be bad. Most of the time, the bearing that fails is located in an idler pulley.

You’ll also want to check the bearing in the spindle housings. To identify a failed bearing in the housing, grab a hold of each side of the mower blade. Make sure you’re wearing a good pair of heavy gloves to prevent cutting yourself on the blade edge. Gripping both ends of the blade, rock the blade up and down to check for movement or noise. If you find either movement or noise, you need to replace the bearing.

Some bearings are able to be replaced in the pulleys and spindle housings, however you may have to purchase a pulley with a bearing already in place. This is common for idler pulleys. Components with failed bearings can cause excessive vibration in your mower. This can cause your belt to come off.

Debris in Grooves of Pulleys on Your Craftsman Lawn Mower

Your Craftsman can kick up a bunch of dirt and debris while you are mowing. Small items can get stuck in the grooves of your pulleys or under your pulleys. Check each pulleys to make sure you don’t have any stones, wood chips or other items caught in the pulleys. There are times I’ve found something as little as dry caked mud that caused my belt to break.

A Craftsman mower belt can break when debris is caught in the deck and in the pulleys. Stress is put on the belt when it has to stretch around the additional debris. This stress can cause your belt to break.

Your Craftsman Mower’s Idler Tensioner Bracket or Spring is Worn

Check the tensioner bracket and spring. The bracket usually has a spring on one side of it and a pulley on the other side. When the spring or the hole in the bracket where the spring attaches is worn, it creates a vibration. This vibration can knock your belt off your Craftsman mower.

Check the bushing in the bracket as it can wear if it hasn’t been kept adequately greased. When the bushing wears, the pulley can begin running at an angle instead of running flat. The pulley can cut into mower also causing a vibration.

Replace any damaged or worn parts on your tensioner bracket. Grease the idler bushing.

Debris Interfering with Proper Tension on Your Craftsman Belt

Grass and debris can collect on your mower deck which can interfere with the belt tension on your Craftsman. If the tensioner isn’t able to work correctly, your belt won’t stay tight. Keep the deck clean by periodically removing the belt covers and cleaning any debris from the area.  

Read my article, “How to Clean Your Lawn Mower for Best Performance” for a guide on keep your lawn mower clean.

Oil or Rust on Your Craftsman Mower Belt

If your Craftsman mower developed an oil leak that dripped onto your pulleys and belts, your belt can slide off your pulleys or slip because it fails to grab hold of the pulleys. Your pulleys need to be kept clean of oil and rust to keep your belts in good condition.

Oil remaining on a mower belt for a long period of time can make your belt swell. Rust on a belt will cause it to dry out and crack prematurely. You should replace a belt that is showing signs of wear and cracking.

Using the Wrong Craftsman Belt

It can be tempting to try to save money and buy an aftermarket belt or have your local hardware store try to match your Craftsman belt with a similar belt. From experience, I choose to purchase a OEM (Original Equipment Manufacturer) belt because they tend to last longer.

I want to be sure I’m using the right kind of belt that can handle the stress the mower puts it through. Not running the right belts can pose problems and safety concerns.

Related Items

How Do You install a Craftsman Mower Deck Belt?

If you find you need to replace your belt because it has become damaged or worn, I have made a handy guide to explain how to install a deck belt on both a Craftsman push mower and Craftsman riding mower. You can find it at “How to Change a Craftsman Mower Deck Belt”.

Your Craftsman is Cutting Uneven

In addition to your belt falling off or breaking, you can have problems with the deck that can give you a bad cut. A loose or worn belt cannot only fall off, but it can keep your blades from spinning fast to give you a nice looking lawn. For other items that can cause your Craftsman mower to give you an uneven cut, check out my article here.

Powered Equipment Team

We're just a guy and a girl obsessed with outdoor power equipment! We are excited to share the knowledge and tips we have learned over our combined 55 years in the power equipment industry. We have both ran equipment dealerships and took pleasure in helping our customers everyday providing equipment repair, parts, purchasing, and business tips to our residential and commercial clients. We hope our blog will help you with your next purchase, repair, or project.

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