Your riding mower deck belt coming off is not typically a serious problem. It’s easy to fix it back and continue mowing.
However, if the deck belt keeps falling off, you might have to look for the problem and fix it to avoid spending much of your mowing time on your hands and feet reattaching the belt.
Your riding mower belt can come off for several reasons, including damaged belts, bearings, or warped pulleys.
Reasons Why Your Riding Mower Belt Keeps Coming Off
To figure out why your mower belt keeps coming off, you might have to set aside some time to troubleshoot your mower, as the problem can come from either the belt or the mower.
Some of the common reasons why your riding mower belt keeps coming off include:
- Damaged Belts
- Stretched Belts
- Damaged Belt Keepers
- Damaged Belt Pulleys
- Cracked Pulley Brackets
- Wrong Belts Installation
- Debris Accumulation
- Oil and Rust Buildup on the Belt
Riding Mower Belt Keeps Falling Off: Causes & Fixes
1. Damaged/ Stretched Belts
This is the most common culprit; a worn or thin belt can easily slip out of the pulleys that hold it in place. Remove your belt and carefully examine it for damage, noting areas with tears and areas that look thinner than the rest of the belt.
If you don’t see any visible signs of damage on the belt but you have been using the belt for an extended period, the belt is stretched. The belt becomes too big for the pulleys and slips off.
Fix: In this situation, the only solution is to replace the belt with a new one because repairing the damaged parts is impossible.
However, be mindful of where you make the purchase to prevent buying a cheap fake deck belt. The best belts are OEM belts, preferably ones containing kevlar fibers.
Your mower technician can recommend the correct brand to buy.
2. Damaged Belt Keepers
A belt keeper is a rod that sits between 1/8″ to 1/4″ away from the pulley; their role is to keep the belt from sliding off; these keepers become bent due to damage or force when a slacked belt hits them.
The belt keeper is most likely the problem if the belt comes off during the lowering and raising of the deck.
Fix: A lawn mower technician is best for this but If you are fixing it yourself, check the individual belt keepers noting if any look out of shape, and adjust anyone not in the right place or shape.
Be careful of the level of force you apply to prevent breakage or permanent bending.
3. Damaged Belt pulleys
The belt pulleys should be level and allow the belt to run freely.
If they get damaged, the belt can slip out during operation. To check this, remove the belt and check each pulley individually, then note if they run freely and if it spins at the same level as others.
Fix: The pulleys are tricky to fix, and it’s recommended you let an experienced technician fix them.
However, if you insist on doing it yourself, you can bend them back with a hammer. They will need replacement if they are damaged completely.
4. Cracked Pulley Brackets/Plates
These are the plates on which the belt pulleys are fixed upon. If the pulleys are fine, check the pulley brackets. If the plates crack, then when the mower runs, the pulleys can shift, and the belt can slip out.
Fix: The standard solution is to weld the cracked parts together. If the plates are damaged beyond the degree a welder can handle, they need replacement. A lawn mower technician can recommend a good store to get a replacement.
5. Wrong Belt Installed
If you replaced your mower belt personally the last time it broke, you might want to check if you bought and installed the right one. There are a lot of belt models available, and if you order online, you can easily make a mistake.
If you also buy a belt that’s too big, it is bound to come off when you are working. This is also the case if you buy from a cheap store.
Fix: If the issue is a wrong belt installation, get a technician to recommend the correct model or go to the store with your riding mower’s complete brand name and specifications. The store will get the right belt for you.
6. Debris Accumulation
Your riding mower belt has to spin with the right tension to work correctly. Debris on the mowing deck can affect the rate at which it spins.
Fix: Clean the mowing deck after every use to keep the belt in optimal conditions. It should be a weekly ritual to clean your riding lawn mower to avoid buildup.
7. Oil and Rust Buildup on the Belt
If your riding mower deck is rusty, the rust can settle on the belt, making it prone to dryness and cracking, which increases its chances of tearing and coming off.
Oil leaks, too, can cause the mower belt to slip off the pulleys if the belt comes in contact with the leak.
Fix: Identify the source of the oil leak and repair it, then clean any oil residue on the mowing deck. Clean rust on the pulleys and belt. If the pulleys are too rusted, replace them.
You might consider getting a new riding mower deck if the issue persists.
8. Extreme Temperature and Weather
This is usually the case in colder regions like Alaska, the belt is near frozen when you wish to use it, and the friction of using it heats it up. This constant freezing and reheating causes the belt to slack and form cracks that could lead to the belt snapping
Fix: Store your riding mower indoors, away from the freezing temperatures; this ensures the belt is at room temperature by the time you wish to use it.
9. Distorted Mower Deck
The mower deck is the platform on which the engines and pulleys rest. Various lawn mower brands have various designs of mower decks. However, should the mower deck become distorted in any way, the pulleys and brackets could shift and lead to the belt slipping off.
Fix: Regularly check the shape of the mower deck, looking out for indentations and changes in its shape. If this happens, you must take the mower to a technician to readjust the mower deck.
How to Tighten a Belt on a Riding Lawn Mower: Simple Steps to Follow
Step 1: Turn off the engine, disconnect the spark plug wire, and then lower the mower deck as far as possible.
Step 2: Locate the tension spring on the mower deck. It’s usually attached to a bracket on one end and the swing arm on the other end.
Your blades should be engaged at this point; push down on this spring and grab the belt; you can disengage the blades with the lever located near the tension spring.
Step 3: Loosen the Bracket. With your blades disengaged, use a wrench to loosen the screws at the base of the pulley bracket. There are usually two and don’t need to be entirely removed, just loosened.
Step 4: Pull the bracket and tighten the screws: With the screws loosened, you need to open the bracket toward you as far as it will go.
Then use the wrench to tighten the screws. Make it tight enough to resist movement from pressure.
Step 5: Engage the blades and test them out: Once you tighten the screws, engage the blades and check the spin.
It should be faster and tenser now. The belt should also feel much tighter.
If this does not make the belt tighter, then you might consider replacing the belt or checking for any of the issues listed in this article.
Again, if your riding lawn mower belt keeps coming off or slipping, it might be caused by one or more of the following:
- Distorted mower deck
- Oil and rust build up on the belt
- Cracked Pulley Brackets
- Debris Accumulation
Follow the recommendations shared above to fix your mower belt problem but if the problems persist, it is best to seek the help of a technician.