MTD Deck Belt Keeps Coming Off

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If your MTD deck belt keeps coming off, it might be due to a shredded belt, worn belt, loose pulleys, defective belt keepers or worn idler tensioner bracket.

In this article, I reveal 11 reasons why your MTD deck belt might continue to come off. And some proven fixes to help you solve the issue. 

Reasons Your MTD Deck Belt Keeps Coming Off

Some of the reasons why your MTD deck belt keeps coming off include:

  • Defective belt keeper
  • Loose or Worn deck belt
  • Defective bearings in the pulleys or spindle housings
  • Worn idler tensioner bracket
  • Oil and rust on the belt

Tools You Need For This Job

Some tools you may need to diagnose and fix your deck belt include:

  • Hammer
  • Work gloves
  • Vice grips
  • New belt

MTD Mower Belt Keeps Coming Off: Possible Causes And Fixes

1. Loose or Worn MTD Belt

This is one of the reasons why your MTD deck belt continues to come off. 

Check the belt and ensure that it is well-fitted. If it is loose, it may be that it is getting stretched or worn from normal use. This will further affect the performance of your MTD lawn mower.

Diagnosis

  • If the belt has a shiny or glazed appearance, or it is starting to show signs of looseness, wear or cracking, it shows that it needs replacement.

Fix

  • Replace the old belt with a new one. 

How to Change the Deck Belt of an MTD Riding Mower

Here are some tips on how to change the deck belt on your MTD riding mower:

  • Shut the engine off, take off the ignition key and detach the spark plug cable (s) to avoid unintentional starting while you are working on your riding lawn mower.
  • Use your deck lift lever to lower the deck to its lowest setting.
  • Remove the deck guards by removing the screws that fasten them to your mower deck.
  • Take off the belt keeper rod from the area of the engine pulley.
  • Loosen but do take off the mower’s idler pulley nuts. This will ensure easy belt removal from the idler pulleys.
  • Use your cellphone or digital camera to take a photo of how the belt is routed before you take it off.
  • Remove the deck belt from around all pulleys including the deck idler pulleys. Do not put your fingers between the belt and any of the pulleys or on the idler spring while removing the belt. Your fingers could get pinched and injured
  • Route your new deck belt in the same way as your old belt.  You can refer to the picture that you snapped earlier or check your operator’s manual.
  • Tighten the loosened idler pulley nuts and place the belt keeper rod back in its right position and around the engine pulley.
  • Remount the belt guards, raise the deck to its highest setting, and reconnect your spark plug cable (s)
  • Put the key back on the ignition switch and start the unit. Allow this unit to warm up a little before you try to engage the mower deck.
  • Set your throttle control to full throttle and engage your cutting deck. Disengage your cutting deck and wait for the blade to stop completely.
  • Engage the mower deck again and check for abnormal noise.
  • Disengage your cutting deck, bring the throttle down to the idle, and shut your riding mower off.
  • Take off the ignition key and detach your spark plug cable. Ground the spark plug cable against the engine to avoid accidental starting before checking the belt.
  • Lower the mower deck to its lowest position and check the belt to be sure that it is properly running through all the pulleys and that there are no signs of damage.
  • Once you have replaced the mower belt and you have inspected other tasks, you can now re-install the spark plug cable back on the spark plug and you are good to go!

Please note: Keep in mind that the instructions for replacing the deck belt of your mower may be slightly different from your model.

2. Defective Belt Keeper

The function of belt keepers is to keep the belt in place. They can become bent, slack and defective, allowing the belt to come out of place. 

Diagnosis:

  • If you notice an extra slack or the belt keeper does not sit close to the belt, it indicates that the belt keepers are defective.

Fix:

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

3. Shredded Belt

A shredded belt can become weak and may break, causing the belt to come off the deck of your lawn mower. Furthermore, an improper belt installation can also cause it to shred. 

Diagnosis

  • Inspect the edges of your belt for signs of shredding and check if your deck belt is properly routed around your pulleys.
  • If the belt is correctly routed, check if the part of the belt guide makes contact with your belt.
  • A shiny or smooth spot on the metal can also indicate that the belt is shredded.

Fix

  • After getting the area that is causing the belt to shred, adjust the bracket or keeper properly to prevent the belt from rubbing.
  • Replace the shredded belt after putting the keepers and brackets in their proper positions. 

4. Defective Bearings in The MTD Pulleys or Spindle Housings

Defective bearings in the pulleys or spindle housings may be one of the reasons why your deck belt keeps coming off. 

Ensure that you check each one of your pulleys and see if they are running parallel and flat to the mower deck.

The pulleys shouldn’t be sitting higher off the deck on one side than the other. 

If they are not running flat, the deck belt can slip off the pulley. This means that there is a defective bearing in the pulley.

The problem may also arise from the spindle housing assembly. An issue with the spindle housing can cause your MTD mower to vibrate and knock the deck belt off the pulley.

Diagnosis

  • Check the idler pulley for any bad bearing. The mower’s idler pulleys come with a sealed bearing and this requires the entire pulley to be replaced.
  • Inspect your housing and make sure that you wear a pair of work gloves to shield your hands from the sharp mower blades.
  • For safety, make sure that you take off the ignition key and spark plug boots.

Fix

  • Replace the entire pulley to fix the issue of defective bearings in the pulleys.
  • Take the spindle housing apart and inspect for a defective bearing. Some spindle housings are sealed and require the entire assembly to be replaced while others can be rebuilt. 

5. Idler Tensioner Bracket or Spring is Worn

The bracket can hold idler pulleys in line. If the spring is weak, it may cause your deck belt to come off.

Furthermore, the tensioner bracket’s hole where the spring attaches may deteriorate and enlarge with use. This can cause your MTD mower to vibrate. 

Diagnosis:

  • Locate the pulley on one side of the bracket and the spring on the other side.
  • Check the bracket’s bushing if it is worn or not well greased. 
  • If the spring appears weak or the tensioner bracket (where the spring attaches) is worn, it needs replacement.

Fix:

  • Grease the idler bushing.
  • Replace the spring.
  • Replace damaged or worn parts of the tensioner bracket

6. Rust or Oil on Your MTD Belt

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 break, dry out or crack.

Diagnosis

  • Check for signs of rust on the belt and pulleys.
  • A low oil level may indicate that you have an oil leak.

Fix

  • 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. Using The Wrong MTD Deck Belt

This is also one of the reasons why your deck belt can come off. Failure to use the ideal belt for your mower can pose problems and safety concerns.

Diagnosis

  • Inspect the belt if it is the right one for your MTD mower model

Fix

  • Ensure that you confirm the part number for the replacement you purchased matches the one listed in the “replacement parts” section of your MTD mower manual.

9. Debris in the Grooves of Your MTD 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.

10. Debris Interfering With Proper Tension On Your MTD Mowing Machine

Your mower belt can become loose and come off the engine as a result of debris build-up. The accumulation of debris on your deck can cause the tension pulley not to move.

This means that there won’t be proper tension on the belt, causing the deck belt to come off. 

Diagnosis

  • Check the mower deck for debris.

Fix

  • Ensure that the deck is clean. 

11. MTD Deck Belt Breaks or Gets Heated Up

This is one of the problems why your MTD deck belt may come off. If the belt breaks, it will come off the mower deck.

Diagnosis

  • If you detect unsatisfactory cuts, turn off the engine of your MTD 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.

12. Extreme Weather And Temperature Can Cause your Deck Belt To Come Off

Your MTD mower belt may continue 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.

Tips to Extend The Lifespan of Your MTD Deck Belt

Here are some tips to follow to elongate the life of your MTD deck belt:

  • Replace damaged belt keepers or brackets.
  • Always clean your MTD 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 factors such as shredded belt, loose pulleys, faulty bearing in the spindle and loose or worn belt can cause your MTD deck belt to continue coming off. 

I hope these recommended fixes will help you solve the issue. If you have tried these troubleshooting tips and the problem persists, it is advisable to call a technician.