It’s frustrating enough to have to stop the mower and pick up sticks and toys in the yard. It’s even more frustrating when you have to stop and reinstall the mower deck belt after it keeps coming off the pulleys. You must find and fix the root cause of the problem so you can get back to mowing.
A Ferris lawn mower belt will break or keep coming off when the deck belt is worn, stretched, or shredded; a belt keeper is damaged; the bearing failed in the spindle housing or pulley; the belt tension is insufficient; the belt is covered in rust or oil, or debris is collecting on the deck.
Before working on or near the mower deck, remove the spark plug wire and ignition key. Take all safety precautions outlined in the Ferris operators manual.
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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 Ferris Lawn Mower Belt Keeps Coming Off Your Deck
Worn Deck Belt
The deck belt on a Ferris mower is a wear item. This means it will eventually need to be replaced due to use. When the deck belt wears, it can begin to slip and fail to turn the blades at a high speed resulting in a bad cut.
A worn belt can also become loose and roll off the pulleys causing a Ferris deck belt to keep falling off. Inspect your deck belt. Depending on the model of Ferris mower you are using, you may have one or two deck belts.
If you notice cracks developing, a glazed shiny appearance, or a stretched belt, you must replace the belt. Another sign you have a worn belt is when the belt sits deep in the grooves of the pulleys.
While some mower owners try to find a comparable belt at the local hardware store, I highly advise against doing this. The belt you get at the hardware store may look the same, but it isn’t always the right type, size, or quality of the belt.
I prefer to purchase an OEM (Original Equipment Manufacturer) belt to ensure I’m getting a quality belt of the right material designed for my mower. The mower deck belt does make a difference to the quality of cut you receive from your Ferris mower.
Damaged Belt Keeper
Some Ferris mower deck belts have belt keepers that sit 1/8″ to 1/4″ away from the pulley. These are installed to prevent the belt from slipping off the pulley and coming off your Ferris.
When the belt has slack in it, it can hit the belt keeper causing the metal to bend. This increases the chance your belt comes off your Ferris zero turn. Check the belt keeper and bracket.
If you find the bracket is bent, bend it back into place. You may need to use a hammer or other tools to straighten the keeper to get it back to its original position.
If you are unable to reshape the bracket and get it to sit correctly on the deck, you should replace it with a new one.
Shredded Deck Belt
A belt can become shredded causing it to become weak and more likely to break. The most common reasons a belt will shred is from incorrect installation or from rubbing on a bracket that has moved out of place.
If you find your belt is shredding along its edges, first check to make sure you are using the right belt and it is correctly routed around your deck pulleys. You should have a decal on your mower with a diagram that shows the belt layout.
If you can’t find it, don’t worry. Refer to your Ferris operator’s manual or a parts diagram to get this information. Once you have confirmed your belt has been installed correctly, check for any brackets that your belt may be rubbing against once your mower deck is engaged.
You may find a shiny wear spot on a bracket where the belt continues to rub. Adjust any brackets you find causing your belt to rub so they no longer rub.
If the bracket you are adjusting has a bushing in it, the bushing may need to be replaced. You must replace a bracket you are unable to adjust to prevent the belt from rubbing.
Lastly, replace the Ferris mower deck belt with a new one once you have confirmed there are no more points on your mower deck the belt is rubbing against.
Bad Spindle Housing Bearing
A bearing may be bad in your Ferris spindle housing assembly. This is the piece on your deck that your mower blade is attached to.
A failed bearing can cause your blade to become unstable and wobble. At high speeds, the wobble can cause an excessive vibration that can knock the belt off your mower.
To check for a bad bearing, remove the ignition key and the spark plug wire. Safely access the underside of your mower deck. Protect your hands with a good pair of work gloves and grab a hold of each end of your mower blade.
Rock the blade up and down feeling for extra movement. You may even hear a knocking noise. If you find your blade is secure to the cutter housing, but there is vertical movement, remove the blade and disassemble the spindle housing assembly (also known as cutter housing).
Chances are highly likely you have a bad bearing in the housing that must be replaced. Inspect the spindle for damage. Replace the bad parts and reinstall. You can purchase the complete spindle assembly or replace the bearing in the housing.
Bad Pulley Bearing
The deck pulley bearings can be the cause of your Ferris belt falling off the pulleys. The pulley is designed to sit flat and parallel to the deck.
When the bearing fails, the pulley may sit at an angle to the deck and wobble as the belt runs along the pulleys. This movement and angle of the pulley; and vibration of the mower can cause the belt to roll off the pulleys.
Check each pulley by slowly spinning the pulley by hand. When you feel resistance, feel a wobble, or hear a noise coming from the bearing, the bearing is bad. The Ferris pulley must be replaced.
Insufficient Belt Tension
Your Ferris has a tensioner bracket and spring on the mower deck to keep proper tension on the deck belt so it doesn’t come off the pulleys and fall off your deck.
Too much tension on the mower deck belt can cause damage to your deck components. Too little tension on the belt can cause the belt to vibrate, slip and come off your Ferris mower.
Debris that collects on top of your mower deck can interfere with the movement of your tensioner pulley.
Check the area around the tensioner bracket and spring and make sure the tensioner, bushing, and spring are in good condition. Remove any debris restricting the tensioner from working properly.
It isn’t only important to keep the belt area of your mower deck clean and free of debris for performance reasons, it is also important for safety reasons as well. Dry debris collected on the top side of your mower deck can catch on fire from the heat of the belt.
Read more about cleaning your mower deck in my guide to finding and fixing mower deck problems. A clean mower will not only improve performance, but it can also extend your mower’s lifespan.
Check your pulleys for dirt buildup in the grooves of the pulleys. When your Ferris mower deck belt has to run around a pulley with mud and debris packed in the pulleys, it is being stretched. This can cause the belt to roll off the pulleys.
The extra stress put on the belt can also cause the belt to snap. To correct this, inspect the pulleys and remove any dirt, stones, grass, and debris you find packed in the grooves of the pulleys or under the pulleys.
Oil or Rust
Rust and oil can ruin a deck belt and be the reason it keeps coming off your mower. Let’s talk about oil first. The oil that gets spilled or leaks on the mower deck can lubricate the belt causing it to slip off the pulleys.
When oil sits on your belt for an extended time, the belt can swell. Look for the cause of the oil leak and repair it. Remove any oil from the deck and mower components. Replace the mower deck belt.
The other item that can get on the belt and cause it to come off your mower is rust. Rust forms when metal components are exposed to moisture. When the rust transfers from the components to your Ferris deck belt, the belt is likely to dry out, crack and break.
Remove rust from the deck and mower deck components. Replace pulleys and components where you are unable to remove all of the rust. Install a new mower deck belt once your deck is cleaned up and free of rust.
Still Having Problems with Your Ferris Lawn Mower?
No matter what type of mower you own, you will run into problems during its life.
Because of this, I have compiled a list of common Ferris lawn mower problems and solutions to help you troubleshoot the next time your mower doesn’t start, keeps dying, has a bad cut, is overheating, or has another issue.
This is an excellent guide to bookmark so you can refer to it when you need help finding and fixing your mower. You can find this guide at Common Ferris Zero Turn Mower Problems and Solutions.