When you buy via links on our site, we may earn an affiliate commission at no cost to you. Learn more.

If your John Deere mower belt keeps coming off, it might be due to a defective pulley bearing, belt guide damage or shredded mower belt.

In this article, I share 11 reasons why your John Deere mower belt keeps coming off and quick fixes to get your mower working efficiently again.

Contents show

Reasons Your John Deere Mower Belt Keeps Coming Off

Some of the reasons why your John Deere mower belt keeps coming off include:

Worn or loose belt
Defective pulley bearing
Shredded deck belt
Belt guide damage
Worn spring or tensioner bracket

Tools You Need For This Job

While troubleshooting, you might need to have the following tools nearby:

Work gloves
Hammer
Vice grips
Screwdrivers
Socket wrench or ratchet
Pliers
New belt

John Deere Mower Belt Keeps Coming Off: Possible Causes And Fixes

1. Worn or Loose John Deere Belt

Over time, the belt of your John Deere mowing machine may wear due to continuous use and exposure to different conditions. This can cause it to become loose and come off in the process.

Diagnosis:

Inspect the pulleys and their bearings. If they are not in place, it indicates that they are not correctly positioned.
If there is a cracked or shiny appearance on the belt, it indicates that the belt is worn.

Fix:

Replace the belt if it is worn or loose.

How to Change the Belt on a John Deere Riding Lawn Mower

Here are some steps on how to change the belt on a John Deere riding lawn mower:

a. Prepare the Mowing Machine

Ensure that you park your John Deere mowing machine on a smooth level. Make sure that you disengage the blades and engage the parking brake.

Put off your mower and take off the key.

Disconnect the spark plug wire and place the wire to prevent it from coming in contact with the spark plug. Use bricks to block your wheels to avoid the lawn mower from rolling.

b. Take Off the Cutting Deck

To remove the mower deck, lower your mower deck to its lowest setting. Disconnect the lift rod assembly from the front of the mower’s frame.

Locate the tension rod and release its bracket (You can find the bracket on the left position of the cutting deck).

c. Remove the Belt Shield And Cap Screws

Make sure that you take off the belt shield and the three cap screws from the topmost position of the cutting deck.

To see the belt and pulleys, you need to lift the belt shield from the topmost position of the riding mower.

d. Disconnect the Idler Spring

Disconnect the idler spring by lifting the mower’s belt tension cord.

This will release the tension from the belt. With this, you will be able to remove your belt with ease.

e. Install the New Belt

Ensure that you wipe the sheaves. Install the new belt as specified in the diagram located under the left foot pedal of your John Deere mowing machine.

f. Reconnect and Adjust the Idler Spring

It is important to always reconnect the idler spring. You can loosen the nut found on the flat idler to adjust the belt’s tension.

Slide the idler slowly in either a forward or backward direction until the belt tension is snug. The flat idler’s nut should be tightened. You should also lower the tension drive belt tension rod.

g. Change the Belt Shield and Cap Screws

You may need to replace the deck’s belt shield. In addition, change the cap screws and secure them tightly.

h. Reinstall Your John Deere Cutting Deck

To reinstall the deck, you need to slide it under the lawn mower. Use the draft arms to line the mower lift brackets and insert the J-pins.

Insert the front lift assembly into the brackets on the mower’s front.

Lift and insert the lift rod assembly into the front of your riding mower’s frame. After that, you may need to fix the mower belt to the engine drive sheave.

Put the drive belt tension rod back in its right position. Raise your cutting deck.

2. Damaged Belt Guide

The function of belt guides is to keep the belt in place. Although your belt won’t touch the guides, they protect the belt from slipping off the pulleys.

They can become bent and defective, preventing the belt from coming out of place.

Diagnosis:

Inspect if there is slack in the belt. If you notice an extra slack, the mower’s belt guides may move out of place.

Fix:

Use vice grips or a hammer to bend the belt guide back in place.

3. Shredded Belt

The shredded or defective John Deere belt can affect the functionality and performance of the mower.

In this situation, the belt will become weak and may break, causing the belt to come off the deck of your lawn mower. It can also shred if the belt is not properly installed.

Diagnosis:

Check the belt edges for signs of shredding and inspect if the belts are rightly routed around the pulleys.
If the belt is properly routed, inspect if the part of the belt guide makes contact with the deck belt.
If you notice a shiny or smooth spot on the metal, then the belt is shredded.

Fix:

Check your owner’s manual to confirm if the belt is rightly installed.
It might be possible to bend some of the brackets to their place. Some brackets can also require a bushing replacement. Brackets that come with bushings may only be available for purchase as a bracket assembly. In this case, you need to contact a John Deere dealer to help you to find the parts that are ideal for your mower deck model.
Adjust or repair the shredded belt

4. Faulty Bearing in The Spindle Housing

It is also important to check any bad bearing in the spindle housing if the belt keeps coming off.

A defective bearing in the spindle housing can make your cutting deck vibrate when you engage the blades. This vibration can cause the belt of your mowing machine to come off.

Diagnosis:

The first step to take is to get work gloves to shield your hands from the blades’ sharp cutting edges.
Rock the blade in an upward and downward position by grabbing hold of each end. While rocking the blade, check for any movement. If you notice a movement or you hear a knocking noise, it indicates that the bearing in the housing may be defective.

Fix:

Replace the bad spindle housing.

5. Idler Tensioner Bracket or Spring is Worn

The bracket is responsible for holding idler pulleys in line. If the spring is weak, the mower’s belt may come off.

In addition, the tensioner bracket’s hole where the spring attaches may deteriorate and enlarge with use, causing excessive vibration in your mowing machine.

Diagnosis:

Locate the pulley on one side of the bracket and the spring on the other side.
If the spring appears weak or the tensioner bracket (where the spring attaches) is worn, it needs replacement.

Fix:

Replace the worn bracket or spring.

6. Bad Bearing in the Pulley

Bad bearings in the pulleys may cause the pulleys not to sit parallel and flat to your John Deere lawn mower deck.

In this situation, the sides of the pulley may be higher than the other. This will make the mower belt not to run properly and can come off the pulley.

Diagnosis:

Rotate each pulley by hand to check for a bad bearing. Move them slowly to be sure that they are turning smoothly.
Check if you can hear a noise emanating from the bearing or if you feel any restrictions. If you detect these signs, then the bearing is bad.

Fix:

Replace the bearing in some pulleys.
If you notice a bad bearing in an idler pulley, replace the entire pulley because it contains a sealed bearing.

7. Rust or Oil on Your John Deere Belt

Rust or oil on the belt can cause it to come off the lawn mower. If oil is left on the belt for an extended time, the belt may swell.

An oil leak may cause oil to get on the belt and can result in belt slippage on the pulleys.

Old brackets and pulleys may develop rust that can get on the deck belt. This causes the belt to crack, dry out or break.

Diagnosis:

Check if the brackets and pulleys are rust-free.
A low oil level may indicate that you have an oil leak.

Fix:

Ensure that the brackets and pulleys are rust-free.
Replace rusty pulleys and inspect the oil level before carrying out mowing operations.
Replace the mower deck belt once you have fixed the issue of oil and rust.

8. Debris in the Grooves of Your John Deere Pulleys

The grooves in the pulleys collect mud or debris that can cause the belt to come off your lawn mower.

The pulley’s material may also cause the belt to stretch and this will allow it to snap or roll off the pulley.

Diagnosis:

Take a look at the grooves in the pulley and check for items (such as debris and mud) that are stuck in the area.

Fix:

Examine the grooves in the pulley and take off any items that may be stuck in this area.

9. Debris Interfering with Proper Tension on The John Deere Mower Belt

It is important to keep the deck free of debris. Your John Deere belt can become loose and fall off if the debris interferes with the proper tension on the belt.

This interference can cause the tensioner not to move and create proper tension on the belt. This can cause the belt to become loose and may fall off.

Diagnosis:

You need to check the mower deck for debris.

Fix:

Keep the deck clean.

10. John Deere Mower Deck Breaks or Gets Heated Up

This is one of the problems that can be associated with your John Deere lawn mower belt. If the belt breaks, it will come off the mower deck.

Diagnosis

If you detect unsatisfactory cuts, turn off the engine of your John Deere mower and check the mower deck carefully for any sign of belt breakage.

Fix:

To fix a broken belt, you need to clean your mower deck, adjust the pulleys and replace the belt.

11. Extreme Weather And Temperature Can Cause The Belt To Come Off

Your John Deere mower belt may keep coming off in extreme temperature changes. This issue is very common in very cold climes.

The reason is that the belt loses its shape in cold weather. If you continue to operate the mowing machine with this problem, It will produce cracks on the belt and break it.

Diagnosis:

Check for cracks on the belt to know if the belt is damaged.

Fix:

Do not operate the mower in extreme temperatures and weather.
Replace the cracked belt with a new one.

11. Loose Pulleys

The belt connects a series of pulleys in the mower deck, which enables the mower blades to engage and spin.

If the pulleys are loose, the entire system would be compromised if the pulleys become loose in their positions.

Diagnosis:

Check the pulleys if they are not loose in their positions
Examine other parts of the pulley-belt system. If the parts are damaged or lost over time, it means that the pulleys are loose and the mower belt won’t stay in place.

Fix:

It is advisable to seek the help of a trusted mechanic that can check the John Deere mower for defective or missing rear hanger clip pins and draft rods.

How To Tighten the Belt on a John Deere Lawn Mower

Here are some tips on how to tighten the belt on a John Deere lawn mower:

The first step to take before handling the mower deck is to turn off the motor. Disconnect the spark plug wires to ensure safety.
To disengage the mower belt, you need to pull the lift lever to disengage the mower belt. Depending on the model, the setting is usually labeled as “transport mode”.
Adjust the belt tensioner. To adjust the belt tensioner, you need to shift the position of the metal bracket to increase the pull of the tensioner cable on the belt.
Unscrew the bolt that joins the bracket to the deck. To lessen tensioner pull, move this bracket to the forward position (away from you). You can also move it backward (towards you) to tighten the pull.
Re-engage the lift lever, re-attach the spark plug and test your mowing machine.

Tips to Extend The Lifespan of Your John Deere Mower Belt

Here are some tips to follow to elongate the life of your John Deere lawn mower:

Replace damaged belt keepers or brackets.
Always clean your John Deere cutting deck after mowing to get rid of debris.
Inspect the spindle housings and pulleys for bearing failure at periodical intervals.
Keep rust and oil from forming on your belt.

Conclusion

Some of the possible reasons why the belt keeps coming off include bad bearing in the pulley, faulty bearing in the spindle housing, shredded belt, worn or loose belt and loose pulleys.

Follow the troubleshooting guide and recommended fixes in this article to identify and solve the issues.

If the problem persists, it is advisable to contact a technician to help you fix the problem.