9 Reasons a John Deere Mower Belt Keeps Coming Off or Breaking (Solved!) (2024)

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You just replaced your John Deere mower belt after it fell off. You ran your mower for a while and it happened again. Having to constantly deal with your mower deck belt coming off is frustrating. You must locate the cause so you can fix it right and get back to mowing that yard.

A John Deere belt can keep coming off your mower when the belt has become worn or shredded. A bad bearing in the spindle housing or pulley; worn brackets and springs; and debris collecting on top of your mower deck can make your belt fall off the deck pulleys.

Take safety precautions before working with the components of your mower deck. Remove the key from your ignition switch and disconnect the spark plug wires to prevent your mower from starting. Wear gloves to protect your hands against sharp edges.

9 Reasons a John Deere Mower Belt Keeps Coming Off or Breaking (Solved!) (1)

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Follow all safety instructions provided in your equipment operator’s manual before diagnosing, repairing, or operating. Consult a professional if you don’t have the skills, or knowledge or are not in the condition to perform the repair safely.

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9 Reasons Your John Deere Mower Belt Keeps Coming Off or Breaking

Loose or Worn Belt

Over time, your John Deere mower deck belt will wear from normal use causing it to become loose and come off.

Look over your belt and make sure it is sitting tight to the pulleys and doesn’t appear worn with a shiny or cracked appearance. If your belt has any of these conditions present, you must replace your belt.

Belt Guide Damage

You may have belt guides on your mower to assist with keeping your belt in place. Belt guides are metal rods that sit next to your pulleys. Your belt doesn’t actually touch these guides. They are added protection to keep your belt from slipping off the pulleys.

The guides can become damaged and bent when there is slack in the belt and this extra slack hits a guide. A bent guide may no longer be able to prevent your belt from coming out of place. Fix the guide by using a hammer or vice grip to bend the belt guide back in place.

Shredded Belt

A belt can become damaged and shredded when it rubs against a belt guide or bracket on your mower deck. The shredded belt can become weakened and break causing it to come off your deck. A belt may also shred when it is not correctly installed.

If you notice the edges on your belt are shredded, first, make sure your belt is routed around your pulleys correctly. Refer to your owner’s manual or an online parts diagram to confirm you have it correctly installed.

Second, if your belt is routed correctly, look for the bracket or belt guide part that is making contact with your deck belt.

A good indication of which part is causing the problem is a smooth or shiny spot that has formed on the metal. Once you find the problematic part, you need to adjust or repair it so it no longer rubs on the belt.

You may be able to bend some brackets into place while others may have a bushing that needs to be replaced. Brackets that have bushings may only be able to be purchased as a bracket assembly.

You’ll have to check with your John Deere dealer to find what parts are available for your model mower deck.

Bad Bearing in Your Pulley

Bad bearings in your pulleys can cause your pulleys to not sit flat and parallel to your mower deck. When they don’t sit level and one side of the pulley is higher than the other, your belt doesn’t run correctly and can come off your pulley.

To identify a bad bearing, rotate each pulley by hand. Move them slowly to make sure they are turning smoothly. If you feel any restriction or hear a noise coming from the bearing, it is time to replace your pulley.

You can replace the bearing in some pulleys. If you find a bad bearing in an idler pulley, you’ll have to replace the whole pulley because it contains a sealed bearing.

Bad Bearing in Your Spindle Housing

The next item to check is the bearing in your spindle housing. To do this, put on a good pair of work gloves to protect your hands from the sharp edges of your mower blade. Grab a hold of each end of the blade and rock it up and down.

You are checking for any movement while rocking the blade. If you feel movement or hear a knocking noise, most likely the bearing in the housing is bad. You must take your spindle housing apart, inspect your bearing and replace it if necessary.

A bad bearing in your spindle housing can cause a significant vibration in your mower deck when you engage your blades. This shaking can cause your belt to come off your John Deere.

Idler Tensioner Bracket or Spring is Worn

Check out the idler tensioner bracket and spring. This is the bracket that holds the idler pulleys in line. You will typically find a pulley on one side of the bracket and a spring on the other side. The spring can become weak causing your belt to come off your mower.

The hole in the tensioner bracket where the spring attaches can wear and become larger. This can cause additional vibration in your mower. When you find either a worn bracket or spring, you must replace the worn part.

Debris Interfering with Proper Tension on Your Belt

You must keep your mower deck clean and free of debris. When debris collects under your pulleys and tensioner, your tensioner may not be able to move to keep sufficient tension on your belt. When this happens, your belt can become loose and fall off.

I just need to mention, debris collecting on top of your deck not only can cause problems with your belt tension, it can also pose a fire hazard.

Dry debris next to friction caused by the heat of the belt running around your pulleys can cause a fire to start on your deck. Keep your deck clean by following the steps here: Finding and fixing mower deck problems.

Debris in the Grooves of Your Pulleys

The grooves in the pulleys can collect debris or mud causing your belt to come off your John Deere. The material in the pulleys causes your belt to have to stretch around the additional material putting stress on the belt. This can cause the belt to roll off the pulley or possibly just snap.

Check the grooves of your pulleys and remove any items that may be stuck or built up in this area.

Oil or Rust on Your Belt

Oil and rust on your belt can cause your belt to come off your mower. Oil, when left on your belt for a long period of time, can cause the belt to swell.

An oil-covered belt can also cause the John Deere belt to slip off the pulleys. Oil may get on your belt when you develop an oil leak that drips onto your belt and deck.

Old pulleys and brackets will develop rust that can get on your deck belt. Rust prematurely causes your belt to dry out, crack and possibly break.

To prevent oil and rust from affecting your belt, make sure your pulleys and brackets are free of rust. Remove any rust you find. If your pulleys are very rusty and in bad condition, replace them.

Check your oil level before each mowing. A low engine oil level may indicate you have an oil leak. When you find an oil leak, make the necessary repairs. Once oil and rust repairs have been made, replace your John Deere mower deck belt.

In Summary

Deck belts can be pricey so the longer you can make them last, the better. Here are a few items that can extend the life of your mower belt to keep it from prematurely wearing or breaking and coming off your mower:

  • Clean your mower deck after each mowing to remove debris
  • Check for rubbing on deck components
  • Keep oil and rust from forming on your belt
  • Periodically check your pulleys and spindle housings for bearing failure
  • Fix or replace any damaged brackets or belt keepers

Your John Deere Mower Deck Can Cause an Uneven Cut

There are many components on your mower deck that can cause a bad or uneven cut when they are damaged or worn. Failed bearings in your pulleys and spindle housings can cause an uneven cut.

A mower deck that isn’t level and has worn blades can also contribute to the problem. To read about all items on your mower that can cause a bad cut read my article: Reasons Your John Deere Mower Cuts Uneven.

Still Having Problems with Your John Deere Lawn Mower?

As a John Deere owner, you will encounter a variety of problems over the life of the equipment. These can include problems with starting, dying while mowing, vibrating, cutting unevenly, and not moving.

To help you identify the reasons your mower is having problems, I put together a handy guide to help you troubleshoot your mower. Check out Common John Deere Lawn Mower Problems and Solutions.

9 Reasons a John Deere Mower Belt Keeps Coming Off or Breaking (Solved!) (2024)


Why does my John Deere mower keep breaking belts? ›

Check pulleys for wear and worn out bearings. A pulley rides on bearings that allows it to spin freely. When a pulley doesn't spin freely, friction is created between the pulley and belt, causing the belt to break.

Why does my mower belt keep coming off? ›

The biggest cause of belts flying off of a mower deck is that the customer does not know that you MUST engage the mower with the engine running at FULL THROTTLE. Engaging the mower at anything less than full throttle can throw the belt off. The next thing that will cause this is an IDLER pulley beating that is dry.

Why does my lawn mower belt keep twisting? ›

Check the pulleys for excessive wear and grooves that would cause them to spin or flip. Also check for any alignment problems or faulty bearings. This is usually a result from worn pulleys and sheaves, or the wrong belts.

Why did my belt break? ›

Over-tensioning can cause the belt to stretch, warp, or break prematurely, while also damaging the pulleys and other components around the system. You can routinely check your belt to assess the tensioning and prevent this from happening in the future. You'll need a tension gauge for this.

Why does my engine belt keep coming off? ›

The only reason for a serpentine belt to come off while the engine is running is because one or more of the pulleys is not aligned with the others. This causes the belt to pull away from the other pulleys and slip off the either the idler pulley or the tensioner pulley.

How long should a belt last on a lawn mower? ›

While mower belts don't have a set expiration date, they exhibit wear signs indicating the need for replacement. Here are the key indicators to look out for: Cracks: Mower belts can develop small cracks over time, especially if exposed to heat and frequent use.

What can cause a belt to continually jump off? ›

We have started with the most obvious and simple items first.
  • Drill is in reverse. Some times, when you have the drill in reverse, it can pop the belt off. ...
  • Improperly routed belt. ...
  • Pulley out of alignment. ...
  • Worn pulley. ...
  • Belt needs replacing.
Oct 31, 2019

How much tension should a mower belt have? ›

The correct tension is achieved when pressure is applied to the center of the longest run and belt is able to be pressed in about ½” from static position.

Why do my sanding belts keep breaking? ›

Improper use and handling, inadequate tension, using the wrong grit, and low-quality or worn-out sanding belts can all contribute to premature belt breakage. Correct usage, applying the right grit for the application, and investing in a quality product can all reduce the risk of sanding belt damage.

Why do timing belts break? ›

The materials a belt is made of will eventually become dry and brittle due to the hot, dry operating condition, weakening the belt and causing cracks. That's why the timing belt is considered a service component with a regular interval to change it. Other causes of timing belt failure include: Excessive wear and tear.


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