Having your belt continue to come off your mower is frustrating especially when reinstalling a belt isn’t always a quick process.
After you’ve reattached it a time or two, it’s time to figure out the real reason your belt falls off so you need longer have to keep messing around with it and can get back to mowing.
A riding mower belt can come off your mower when brackets, belt keepers, or idler springs are worn or damaged; your bearings are bad in your pulleys or spindle housings, or debris is interfering with the tension of your deck belt.
I’ll go through the different items to inspect on your mower deck to identify the reason your belt keeps falling off. You will be able to repair your problem and not have to keep reinstalling your belt.
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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.
Reasons Your Riding Mower Belt Keeps Coming Off
Loose or Worn Mower DeckBelt
Your mower belt will wear from normal use. This wearing can cause your belt to become stretched and loose causing it to come off your riding mower.
When your belt becomes worn or has cracks or a glazed shiny appearance, it is time to replace your belt.
Mower Belt Keeper Damage
Many riding mowers use belt keepers to assist with keeping the mower belt in place. This is a rod that sits between 1/8” to 1/4” away from the pulley. The belt doesn’t sit against the belt keeper.
The keep just prevents the belt from coming out of place and slipping off the pulleys. Your rod keepers can bend when a belt hits a keeper because of slack in the belt.
This can allow your riding mower belt to come off the pulleys. Look for any damage to the belt keepers and adjust the keepers to the correct positions.
You may need to use a hammer or other tool to straighten the keepers. If this doesn’t work, you’ll have to replace them with new belt keepers.
Shredded Mower Deck Belt
Rubbing your belts around brackets on your riding mower deck can cause your belt to shred. Another reason your belt can shred is when it is not installed correctly around your pulleys.
First, you’ll want to make sure your belt is routed correctly. There may be a diagram decal on your mower showing you how the deck belt needs to be routed. If you can’t find a decal, refer to the diagram in your owner’s manual.
Next, if your belt is routed correctly, you need to find a bracket that is out of place. Look for a bracket that is smooth and shiny from the belt rubbing against it.
Once you identify the bracket that is causing your belt to shred, adjust it so it no longer rubs. If your bracket has a bushing in it, you may be able to replace the bushing or you may have to buy and replace the whole bracket assembly.
Take time to find what is causing your belt to shred so you don’t continue to go through multiple belts.
Riding mower deck belts are pretty expensive and can run between $80 and $250 for a good OEM belt. Solving this problem will keep you from spending more money.
Damaged Pulleys or Spindle Housing Bearings
A damaged or worn bearing in your pulleys and spindles can cause your riding mower belt to keep coming off. Check the bearings in your pulleys and spindle housings for wearing.
To check the bearings in your pulleys, you’ll want to slowly spin each pulley and feel for a restriction. In addition to the restriction, listen for bearing noise as you turn each pulley.
When you feel a restriction, hear bearing noise, or notice the pulley isn’t sitting flat and parallel to the deck, you need to replace your riding mower pulley. The other area you can experience bearing failure that can cause your belt to fall off is in the spindle housing.
To check this, put on a good pair of work gloves and grab a hold of each end of the mower blade. Rock the blade up and down. You’re checking for movement in the blade or a knocking sound indicating a bad bearing.
When you feel this, remove the spindle housing, inspect the bearing, and replace it with a new bearing if you find it’s bad.
Some riding mowers manufacturers will not sell only the bearing and you will be required to purchase the whole spindle housing assembly. Repeat this procedure to check each spindle housing in your deck.
Idler Tensioner Bracket or Spring is Worn
Your riding mower deck has a tensioner bracket and spring that holds the idler pulley in line. Usually, you’ll find a pulley on one side of the bracket and a spring on the other side.
The spring or the hole in the bracket, that the spring attaches to, can become worn.
This can cause vibration in your mower deck or won’t hold proper tension causing your riding mower belt to come off your deck. You’ll need to replace the bracket or the spring if they break or become worn.
Debris Interfering with Proper Tension
The belt on your riding mower must have the proper tension to keep your belt from falling off your mower deck. Debris can interfere with this tension when it gets stuck under your tensioner or collects so your tensioner is unable to move.
Keep your mower deck clean of debris by cleaning it off after each mowing. Not only do you want to keep it clean so your mower deck belt operates correctly, but you also need to do this for your safety.
Dry debris that collects on your riding mower deck can catch on fire when heat is created with friction from the belt.
Check out my articles, “How to Clean Your Lawn Mower for Best Performance” and ” How to Find & Prevent Substantial Lawn Mower Deck Problems ” to learn more on how to keep your mower clean and in good condition to extend your mower’s lifespan.
Debris in the Grooves of Your Pulleys
Debris can also build up in the grooves of your pulley which causes stress on your mower belt when it needs to stretch around additional material. Your riding mower belt can come off or snap.
Check for mud and debris buildup in your pulleys. Clean them so your belt sits in the groves correctly.
Oil or Rust on the Belt
Rust buildup on your deck and from your pulleys can collect on your belt causing it to become dry, and more prone to cracking and coming off your riding mower.
Oil buildup from an oil leak that dripped onto your deck can cause your belt to slip around the pulleys and come off as well.
Repair the oil leak or remove the rust around your pulleys. If your pulleys have a lot of rust on them, replace your pulleys. Once these items are taken care of, you must install a new riding mower deck belt.
Riding mower 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 riding lawn 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