Lawn tractor mower belts. Mower Deck Belt Replacement – Step by step

Mower Deck Belt Replacement – Step by step

Replacing belts on your mower is like replacing tires on your car; there are only so many miles in them. Replacing a deck belt can be a challenge, especially if the mower throws the belt and you don’t know the routing, but we’ll get it figured out!

Getting the correct belt is the first important step. Some manufacturers place a label detailing the belt part number and belt routing. Try under the hood or under the footrest; if not, check out “Belt routing.”

How To Change The Deck Belt On A Troy-Bilt Riding Lawn Mower

Deck types vary. Some are easy to work on, some not so much. It’s important to check over the deck looking for any damaged or loose components, especially if your old belt was damaged and not just worn out. You don’t want to damage the new belt needlessly.

Most mowers won’t require deck removal to fit the belt; others will. So take some time and consider the routing, don’t put extra work on yourself. Take lots of photos; it saves time and head-scratching later.

What’s Involved?

Fitting the new belt means removing some plastic protective covers. And in most cases, it involves wrapping the belt around the pulleys and making sure the belt guide (guide not on all pulleys) is on the outside of the belt. The last pulley to fit is the crank pulley (engine pulley).

Tensioned or Not

A tension-ed belt is a deck drive belt that is always tight on the pulleys. Push-button blade engages type mowers usually run an always tension-ed belt. Replacing it will require manhandling the belt onto the side of the crank pulley, then turning the crank pulley clockwise by hand until the belt slips on.

If your mower has a lever, then you likely have a slack belt which is then tensioned by moving the blade to engage the lever. This type of belt is easier to replace and will take no time at all.

Tensioned – This type of belt is always tight on the pulleys.

Un-Tensioned – This type of belt setup is slack on the pulleys until you engage the blades.

What Deck Type?

Cutting deck setup types vary from side discharge; rear discharge; mulching decks; front decks; cutting, and sweeping.

They may have features such as single-blade; twin-blade; tri-blade; tensioned belt; manual tensioned belt; electromagnetic blade engagement; fan assisted deck; timed overlapping blades, and so on.

The one thing they all have in common – is the deck drive belt. It’s how engine power is transferred into cutting power.

Timed Deck

A timed deck means both your mower blades are set at a fixed angle in relation to each other. The toothed belt maintains the blade position; this allows the blades to overlap.

Some say the overlapping blades give a superior cut; I like the lawn finished with the overlapping twin cut, especially the smaller decks.

This deck type is also referred to as an interference deck. They call it Interference because if the blades go out of time, they’ll smack each other.

Resetting the timing of the blades or replacing the belt is a job that can be done without much difficulty, but it does require removing the deck, tension assembly, and various plastic guards. No special tools are needed.

Rear – Rear discharge is great at collecting grass but doesn’t like long grass so much.

Timed – Timed deck has a toothed belt that can break or slip out of time. Timing the blades allows them to overlap.

Mulching – Some decks will have a flap that closes off the chute when the operator wants to mulch.

Side Discharge – Side discharge is great for tall grass and rough terrain.

Measuring The Belt

A belt will be marked with a type code, length, and part number. Belts are usually measured by their inside length (Li) or outside length (La); if you can find this info on the side of your old belt, great! But usually, it’s worn away.

Some mowers like Husqvarna place a sticker inside the hood with a list of helpful part numbers like belts, filters, plugs, etc.

What Belt Width? – The width and depth of a belt are also very important. A new V belt should fit snugly into a v pulley; the belt should sit just proud of the pulley’s shoulder. A belt that sits further down into the pulley is worn out.

What Belt Length? – If your belt was shredded, then you’ll need your make and model number to order the correct belt. An easy way to measure an old belt – use a string to follow the outside of the belt; now measure the string.

This measurement will be marked on belts by the letters La (outside measurement); alternatively, run the string around the inside of the belt; this measurement is the Li measurement.

A faster way to measure an intact belt is to make a circle of the belt and measure inside to inside, then multiply by 3.14. The result is the Li belt size.

Sizing – Sometimes easier said than done!

Markings – Check under the hood of your mower; you may get lucky with a part number sticker, but be cautious with the Husqvarna labeling; they are often wrong belt part numbers.

Check your old belt for markings; if none, get the tape and some string. These belts are measured in mm.

Pulley – The new belt will be the full width of the pulley. Worn belts usually stretch in length and become narrow in width.

Check Belt Routing

Belt routing, needless to say, is important. On some mowers, it’s possible to put a belt on the backways, which makes the blades turn backward. Not much use for yard work.

If you can, make a diagram or take some pictures of the old belt in place. First, you’ll need to remove both plastic protection pulley covers, one on each side. Some mowers have a handy sticker showing the deck belt routing under the footrest.

That’s great advice, but what if your belt has snapped or derailed? Then you’ll need to check out the links below. Bear in mind, even if you don’t see your maker in the list, check the link out anyway because lots of make share the same decks.

Look at the pulley configuration to see if yours looks similar.

Belt Routing Links

The following link to Google belt routing pictures:

Sticker – Check under the footrest of your mower; some models have a belt routing sticker. This sticker is on a Husqvarna tractor.

Check out the Amazon link below for deck belts.

What Belt Type?

Belts are belts, right? Well, No. The correct belt is crucial. An ill-fitting or wrong-type belt will cause endless trouble. Throwing the belt, vibration, poor cutting, and collecting, and because the belt doesn’t fit correctly, it won’t last very long. I had one customer who fitted a belt that was so tight it broke the end of the crankshaft. Ouch!!

There are many different types of belts; however, when it comes to lawnmowers, they are usually fitted with a standard V-type belt. Other belts used are AA belts, timed belts, and poly V belts.

Sure, you can fit a basic quality belt with a polyester cord, but it’s going to wear out quickly; for durability, you’ll want Kevlar; they cost more but last a lot longer. Some models will only work well with OEM belts, like John Deere and MTD.

I recommend fitting only OEM (Original Equipment Manufacturer). Fitting a belt can be a challenge. Reassembling and discovering what doesn’t work right can be demoralizing.

V Belts

V belts are so-called because of their cross-section shape (wider at the top than the bottom). They are used almost exclusively to drive power from lawn tractor engines to their transmissions. They are also used to drive deck blades. The V belt drives power from one side of the belt only.

They come in different heights/widths and are marked type A, B, C, D. The most common V belts used on mowers are the A and B types, and obviously, they come in a long list of lengths.

lawn, tractor, mower, belts, deck, belt

Each belt is marked by type and belt length; it may also have a part number. Unfortunately, the markings usually wear off, making the ID process difficult.

AA Hex Belts

The AA belt is a double-sided hexagonal belt; it is mostly used on tractor mower decks to drive the blades. The belts are unique as they have the ability to drive from either side of the belt.

AA Hex Type – This is a double-faced belt; it gives greater flexibility to deck design, as it allows both sides of the belt to drive. It’s used on higher-end tractor decks.

Toothed (Timed) Belts

A mower-toothed or timed belt does two jobs, it transfers power and, at the same time, keeps the mower blades from hitting each other. The toothed belt is a very exact belt in that the teeth of the belt must match that of the mower cogs.

Timed Belt – This type of belt has become more popular in recent years. It’s fitted to mower decks with overlapping blades.

A Type

A Type.This is the most common type of lawn tractor belt; it’s used by many lawn tractor drive systems and most decks too.

B Type

The B-type belt is a heavy-duty A belt; it’s an older well-fed brother.

Check Belt Wear

Belts have a difficult job and can be the cause of various issues. Regular inspection will tell you if your belt is at the end of its life. Things to look for are flat-spotting, glazing, cracking, fraying, and contamination.

As you know, a V belt should sit just proud of the pulley shoulder; if it’s a lot lower than the shoulder of the pulley, it’s worn out.

How Long Do They Last?

The life of a belt is hard to gauge, it really depends on how much grass you’re cutting and how heavy the workload is, but usually, we’re talking years. Typically a belt should be changed after 3-4 years, but we know this doesn’t happen.

A worn or damaged pulley can shorten the life of your belt. An engine or transmission oil leak can destroy the belt, you can try cleaning it, but it causes slip. A derailing belt can get twisted and damaged, and a mower that throws belts regularly probably has a worn or damaged pulley.

But the real killer of belts – tall, heavy grass jams the blades, which causes flat spots on the belt. The flat spot will then cause a lot of vibration, which in turn can throw the belt.

Belt damage is usually caused on the first cut of the season when the grass is heavy. So if your grass is tall and heavy, just take a little off on the first pass and make a second pass with the deck a notch lower. Yes, it’s twice the mowing, but it’s better for your mower and your lawn.

Flat Spot – Flat spotting is usually caused when the blade jams, but the engine pulley keeps running. This has a grinding effect on the belt.

The flat spot will cause excessive vibration in the mowing deck. The fix is – Replace the belt.

Blistering – This can happen when a belt gets old, and the material starts to break down. Your mower won’t cut or collect very well. Better to take care of it now, before it breaks.

Glazing – This belt has a shiny hard surface that is not much good for traction. A belt like this will cause horrible vibration in the mowing deck.

Frayed – Wear and tear, this belt is at the end of its useful life.

Cracked – Natural wear and tear

Check Pulley Wear

A pulley’s job is to route the belt around the chassis of the mower or mowing deck and transfer power from the engine pulley to the driven pulleys. As a rough guide, pulleys usually wear out at the same time as a belt, so best to check them while you have the belt removed.

Tension and idler pulleys should move freely, be quiet when spun, and should feel smooth when turned. If they’re worn, now’s the time to take care of it; when a pulley bearing breaks, it will likely damage the belt.

Spin To Test

You don’t need to remove them to check. Spin them while the belt is off; they should be smooth and quiet. Changing them now is easy.


Most pulleys come with the new bearings pressed in place; the exceptions are driven pulleys (Mandrel, engine, or transmission pulleys).

Pulley Types

Pulleys come in all sizes, some metal and some plastic. Tensioners and idlers will have a bearing fitted, and when it wears out, the whole pulley is replaced. Pulleys are usually broken into two main types, flat or V.

A flat pulley is not a driven pulley; it runs on the back of the belt, which isn’t powered (unless it’s on a AA belt).

A V pulley can be driving, driven, tensioner, or idler. A V pulley is described as a driven pulley if it’s connected directly to the output, such as a transmission or a blade Mandrel.

The driving pulley is the engine pulley; it’s the pulley supplying the power. Both the driven and driving pulleys are fixed to shafts using a key and key-way.

A tensioner pulley is part of a moving arm, which, when operated, applies tension to a belt. A tensioner pulley can be a flat or V pulley.

A stationary pulley is usually known as an idler, and its job is to route the belt around the chassis of the mower or mower deck; they can be flat or V-type.

Pulleys – Metal or plastic, V type or flat, driven or idle. So many choices.

V Pulley – This is a V pulley; the driving side of the belt is making contact with the pulley.

Flat Pulley – A flat pulley on a V belt setup is never a driven pulley. Its job is to change the direction of the belt and guide it to the next pulley.

Fitting A Belt

Fitting a cutting blade deck belt that is just worn is the easiest, as you can see the routing of the old belt, and make a diagram or take pictures. Removing the old one also gives you an idea of how challenging fitting the new one will be.

As you know, there are a few variations of deck belt setups; most mowers will have one belt to drive the blades that are either a tension-ed or a un tension-ed belt. The belt can be fitted to both of these types of setups without removing the deck from the mower.

The timed belt setup is a little more involved but not complicated. It has two belts as do so some of the larger John Deere mowers. They can be a challenge as they have many pulleys, and you’ll need to remove the deck.

Pulley Covers

Likely you’ll have already removed the two plastic pulley protection covers, one on each side of the deck. Usually, 2 or 3 screws on each side. They’re not there to protect the pulley. They’re there to protect us from catching body parts in the pulleys.

The latest generation mowers are far more challenging to access as the nice people in the health and safety dept. have been working nights and weekends to find new ways to challenge us.

Removing Belt

Here’s a quick run-through of what we’ll be doing, but it’s all covered in the steps below with pictures. With the covers removed, start by removing the belt from the engine pulley. Often the engine pulley will have a belt guide; its job is to prevent the belt from derailing. Depending on the type of belt guide (if fitted), you may need to remove them first.

As you know, some belts will be tensioned all the time. By tension-ed, I mean the belt is tight around the engine pulley all the time.

The belt tensioner will allow for movement (it’s spring-loaded) so the easiest way to do this is by pulling the belt over the side of the engine pulley and then, with both hands, turning the engine pulley until the belt falls off (Removing the spark plug makes turning the pulley easy).

With the belt off the engine pulley, it’s easy to guide it off the other pulleys. Check your old belt against your new belt, just to be sure.

The un-tensioned belt is simple to fit, and by un-tensioned, I mean the belt is loose around the engine pulley until you engage the blades. The belt can usually be maneuvered around the guides without much trouble.

As with the tension-ed belt, remove the belt from the engine pulley first.

Fitting Belt

Reference your diagram or pictures of routing. Refitting the belt is identical except in reverse order, fitting the engine pulley last by pulling the belt onto the side of the pulley and turning the engine over.

Timed Belt

Most mowers have a simple deck belt setup, like the one covered in this guide is more complex. The demo mower used here has two deck belts driving the mowing deck.

The first one is the main input belt which is powered directly by the engine. This belt is easy to replace, and you don’t need to remove the deck, just some plastic covers.

The second belt is the output belt, and it turns both blades in time. This allows the cutting blades to overlap and catch that annoying tuft of grass you sometimes see in the middle of your cutting strip.

To replace the output belt also known as a toothed belt or timed belt, we need to remove the deck from the mower. It’s not difficult to do, and the whole job shouldn’t take more than an hour.

This guide covers a timed deck belt replacement procedure. Most timed decks will look something similar. It’s more complex than other deck belt setups but not difficult to work on. In this guide, I will: remove the deck; inspect belts; replace the belt; tension the belt; set the timing of the blades.


No special tools are needed on this mission, but an impact gun would make life a lot easier. When you try to open bolts attached to pulleys, they tend to spin, which is a real pain. Sure, you can wedge it or grab it with grips, but you risk damaging the face of the pulley, and that in turn can damage your new belt. Nooo!

The impact makes small work of pulley bolts, and the better brands have a torque setting built-in which makes reassembly a gift. It’s a super tool to have in the trunk of your car; it makes changing a wheel look NASCAR slick. So treat yourself or drop a few hints before fathers day.

Chute – On this model mower, the chute is fitted through the center of the mower. Not all mowers will have a chute like this. If your mower is side discharge, then you don’t have one.

Remove – As said earlier, you may not need to remove your deck to fit a belt. On this model mower, removing to fit the belt just makes life a little easier.

Pins – Locate the deck arms. Most mowers will have one at each of the four corners. The deck will be fixed to the deck arms with Cotter pins. (Some may have nuts and bolts) Remove the two front pins and the two rear pins.

Slide – The deck will be free to move forward, which allows you to remove the deck drive belt from the engine drive pulley. In some cases, you may have a cable to remove; this depends on the blade engage type.

Push – With all pins removed and belt off, just push the deck sideways and it will pop off the arm bushing mounts. Apply some grease when refitting. Hey, I make that sound easy!

Inspect – Go ahead and turn the deck over to inspect the blades and blade boss (blade attachment). It’s likely that the blades are damaged; if they are, replace them.

Bent – If your blades are bent or worn, now is the time to take care of them. Replacement blades are easy to fit when the deck is off.

Boss – When your blade hits something hard, the blade boss pins are designed to break; this saves damaging more expensive components.

Replace – Check washers and bolts for damage. Blade bolts and washers are specially designed, so only use the original kit.

Remove – Remove plastic protection covers.

Pulley – Remove the drive belt tension assembly.

Key – Remove and store the key and the spacer ring safely.

Remove – Remove the timed belt protective cover.

Belt – Remove the broken belt, and check for damage.

Loosen – Loosen both pulley bolts; the bolts are positioned on the underside of the pulley.

Remove – Remove the two guide bolts. Remember to fit these after fitting the belt, but tighten them last.

Loosen – Loosen the two guide bolts.

Loosen – Loosen the lock-nut on the adjusting bolt, and thread it all the way out.

Push – Now push the tensioning assembly in all the way so it hits the adjusting bolt.

Set to 90° – Set the deck blades at 90° to each other.

Mark – Now mark the two main blade pulleys and the deck body as per the picture. Marking them with paint gives us a clear reference point when fitting the new belt.

Align – Keep your paint marks aligned and fit the belt to the tension assembly last.

Check – Check your paint marks again; it’s OK if you’re out by one or two teeth.

Routing – This is a typical timed belt routing.

Adjust – Adjust belt tension first, and tighten down the lock-nut. Do not tighten pulley bolts or guide bolts at this stage.

Check – Check belt tension as you adjust. Leave some play in the belt; it should deflect by about 1/2″ at its longest run.

Check 90° – Check that the blades are at 90 degrees. If all is OK, go ahead and fit the guide bolts, but don’t tighten them yet. Tighten the two pulley bolts, and now tighten the four guides.

Rebuild covers and fit the deck in reverse order; that wasn’t so bad!

How to easily change deck belt on John Deere X300 M154621

Related Questions

Why does my deck belt keep breaking? Common reasons new belts keep breaking:

Why does my mower deck shake? Mower decks commonly shake because:

  • Engine not at the correct rpm
  • Engine not running correctly
  • Blades damaged
  • Deck belt damaged or worn
  • Spindle bearing damaged or broken

As you’re a MacGyver type, you’ll likely find the Riding mower troubleshooting and the Video repair library useful.

Hey, I’m John, and I’m a Red Seal Qualified Service Technician with over twenty-five years experience.

I’ve worked on all types of mechanical equipment, from cars to grass machinery, and this site is where I share fluff-free hacks, tips, and insider know-how.

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Riding Mower Belt Keeps Coming Off: Reasons and Fixes

If your riding mower belt keeps coming off every time you take it out for grass cutting, it might be indicative of a more serious problem. This is included in the list of most common problems with lawn tractor-type riding mowers.

Instead of wasting time putting the deck belt back each time, you need to uncover what is causing this frequent slippage to occur. This complete guide will discuss why a belt repeatedly keeps coming off and how to fix each cause.

  • Why Does Your Riding Mower Belt Keep Coming Off?
lawn, tractor, mower, belts, deck, belt
  • – The Belt is Damaged
  • – Belt is Full of Dirt
  • – A Shredded Belt Comes off Easily
  • – The Wrong Belt Has Been Installed
  • – An Oil Leak Might Cause It To Slip
  • – The Mower’s Pulleys Are Damaged
  • – The Bearings Are Damaged
  • – The Bracket Below the Pulleys Is Damaged
  • – The Belt Is Misaligned
  • – The Belt Is Stretched
  • – Replace a Damaged Belt
  • – Keep the Deck in Perfect Condition
  • – Get the Wrong Belt Replaced
  • – Replace Faulty Bearings
  • – Fix the Pulleys if They Are Damaged
  • – Weld a Split Belt Bracket

Why Does Your Riding Mower Belt Keep Coming Off?

Your riding mower belt keeps coming off because of several possible causes such as a damaged, dirty, or incorrectly installed belt. This problem can also be due to an oil leak, damaged mower pulleys, damaged bearings, or a misaligned or stretched out belt.

As you can see, there are several potential reasons why the mower belt keeps coming off every time you use a riding mower. Here are some other potential reasons to check out. It is important to diagnose the root problem first before planning on a solution.

– The Belt is Damaged

You can take only so much work from the belt of a riding lawn mower before it gives up. We appreciate it if you lend your precious mowers, like the cub cadet mower, to neighbors and friends.

However, the mower is more likely to be used improperly and its parts damaged. Once the belt is damaged, it struggles to stay on the belt keeper and tends to come off at the slightest inconvenience.

– Belt is Full of Dirt

Dirt will inevitably accumulate over the belt of the riding mower or under the pulleys as time passes. The belt and its pulleys are close to the ground and on the receiving end of debris as you ride the lawn mower across the lawn.

When the belt accumulates dust, grass clipping, wood chips, and stones, the pulley has a harder time moving across the mower deck. The result is that the belt keeps coming off repeatedly every time the mower is used.

That is why cleaning the mower and removing potentially hazardous solid objects from the ground before use is very important. It might surprise you, but something as trivial as dirt on the mower belt might damage it.

– A Shredded Belt Comes off Easily

Shredding is common among belt problems, especially if the mower is too old. This happens when the belt regularly rubs against the belt keeper or bracket. When the mower hits a particularly rough spot, the belts get a bit displaced, after which it keeps rubbing against the belt keeper more forcefully.

The segment of the belt that is shredding will appear shinier than the rest of the belt. There will also be shiny spots on the belt keeper and the bracket. See whether aligning the belt back in place helps with this problem. You might have to adjust the parts against which the belt keeps rubbing into.

The shredding mostly happens because of an out-of-place belt bracket. The bracket can be salvaged if its brushings are still intact. However, if the brushings have been damaged, the bracket will have to be replaced.

– The Wrong Belt Has Been Installed

You could have bought an incorrect belt when replacing your last mower belt with the current one. It is common to get the wrong belt type, which then fits poorly and keeps coming off. We see this problem happening more when people order their belts off the internet.

There could be many reasons you have ended up with the wrong belt for the mower. You may have been trying to save money and bought a cheap alternative for your branded John Deere, or the one you ordered may need to be bigger for your mower’s engine.

– An Oil Leak Might Cause It To Slip

If an oil leak occurs in your lawn mower, most spilled oil will fall over the rotating mower belt. The belt will naturally slip over the belt keeper or the pulleys repeatedly until the oil is cleaned and the leak stops.

Oil leakage from the fuel tank occurs either because it has been overfilled or improperly sealed. Sometimes the spill might occur because of damage to internal parts and will need a professional mechanic to fix it.

– The Mower’s Pulleys Are Damaged

When the pulleys need to be fixed, the belt will keep slipping off repeatedly. Two pulleys keep the belt of a riding mower running between them. These pulleys always need to be on the same level so that the belt stays in place.

Unfortunately, it is very common for one or both pulleys to become damaged over time. This creates an imbalanced surface for the belt from which it keeps sliding. To confirm that the pulleys are damaged, you must remove the belt first. Only then will you get a better look at the condition of the pulleys, along with what needs to be done to correct them.

– The Bearings Are Damaged

For most rider belts, such as the cub cadet mower, faulty bearings within its pulley apparatus might cause the belt to slip. Even if a single one of the bearings are damaged, this will cause the pulleys to become loose or uneven on either side of the belt.

Again, you will have to turn the mower off, disengage the spark plug and remove the deck to inspect the bearing; if you are not that experienced in the technical know-how, then it is best to refer to someone who is.

– The Bracket Below the Pulleys Is Damaged

Once you have checked the belt and the pulleys and found no problem, a less common culprit might be the idle tensioner bracket or the plates below the pulleys. To observe them, you must fully expose the deck by removing the belt.

Carefully inspect the bracket and the plates to see if they are bent, cracked, or have incurred any other damage. Remember that these are very sensitive parts, so when they get damaged, the balance of the pulleys becomes off and the belt gets removed every time.

– The Belt Is Misaligned

This is the easiest problem to fix when a mower deck belt keeps getting loose for no apparent reason. When you get your mower checked or do something to it by yourself, the belt might get accidentally misaligned.

Even if it is slightly out of place, it immediately comes off during use. This problem will immediately be fixed by getting a professional to align the belt on the pulleys. Make sure you do not attempt to disassemble or take apart your lawn mower unless you know exactly what you’re doing. Making a mistake can lead you to more costly repairs down the line.

– The Belt Is Stretched

Sometimes the belt stretches too much when used for a long time. We are talking about good-quality lawnmowers that have been used for several years. Again, you can only find this out once you have gained access to the deck and inspected both the belt and the pulleys extensively.

A stretched belt will be too large to stay in place with the required belt tension and will frequently become loose. A stretched belt cannot be prevented, and you will have to replace it with a new one.

What To Do if Your Riding Mower Belt Keeps Coming Off?

If your riding mower belt keeps coming off repeatedly, you first need to find out the cause and then fix that problem. Replace the belt and its bearings if they are damaged and make sure to repair the other parts that have been affected.

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Other methods you can try include keeping the deck in perfect condition, fixing the pulleys if they have been damaged, and doing some welding if the belt bracket has been split.

– Replace a Damaged Belt

If the belt has been damaged from overuse or improper use, it will simply have to be replaced. Unfortunately, there is no process or way to repair or fix a damaged belt. Replacement belts are easily available in the market at various price ranges.

Our advice would be to steer clear of cheap ones because they only last so long. Instead, increase your budget and go for the slightly pricier OEM belt that will last longer. Cheap belts will usually break down much faster than those that are made with higher quality materials. Purchasing cheap belts might be more affordable for now, but it will cost you more in the long run.

– Keep the Deck in Perfect Condition

If the belts keep coming off and you notice dirt and dust accumulated on the mower deck, then this is your cue to clean it right then and there. For thorough cleaning, it is best to remove the blade first. This way, you will have unrestricted access to the entirety of the deck for cleaning.

Whether you make your cleaning solution using soap and water or buy one from the market is totally up to you. First, use a metal putty knife or a wire brush to scrape off the dirt that seems strongly stuck to the surfaces. Then use a hose with the cleaning solution to clean the deck. You can also keep the blade on while cleaning the deck and use a long-handled brush to reach the corners.

It might seem like a hassle, but you must clean the lawn mower’s deck after every use. This can be accomplished within five minutes and will prevent dust from sticking stubbornly on the belt.

– Get the Wrong Belt Replaced

It isn’t very pleasant to buy a mower deck twice if you made an honest mistake the first time. See if you can exchange the wrong one with the new one to save a few bucks. This time, make sure only to buy the right size and best-quality belt from an authentic seller. It helps if you have a trusted mechanic or hardware store owner who can give you professional advice in this case.

– Replace Faulty Bearings

Once it has been established that the fault lies in damaged bearings within the pulley apparatus, you will have to replace it. If your mower has an idler type of sealed pulley, the whole pulley will have to be replaced due to a faulty bearing. In case of an unsealed pulley, you can replace the bearing and keep the pulley.

– Fix the Pulleys if They Are Damaged

Before you get to fix the pulleys, you have to remove the belt first. Start by removing both the right and the left side covers of the belt. The spring connecting the pulleys to the PTO needs to be removed next. After this, you can easily remove the mower belt and inspect the pulleys.

In a lot of cases, what happens is that the pulleys get bent after bumping into hard objects on the ground. Try to bend them back into shape and see that both pulleys are on the same level.

Sometimes, the pulleys are so damaged that nothing can fix them; in that case, replacing them is going to be the only option. This time, go for idler pulleys because they are better at keeping the belt in place.

– Weld a Split Belt Bracket

It is common to see the belt’s bracket split into two parts upon inspection. In most cases, this happens when the mower hits a particularly hard spot on the ground or a stone accidentally enters the deck.

Don’t worry because a split bracket can easily be welded back together. Because most of us do not keep a welding torch at home, a mechanic nearby can help you do this job better.


In the upcoming section, let us conclude this extensive guide on the reasons behind a loose lawn mower belt. Make sure that your safety is always the first priority — wear protective clothing such as safety goggles and long sleeved shirts when working on machinery like this.

  • It is only natural that the belt will become loose over time from prolonged mower use and will have to be replaced by a new one.
  • See if the pulleys are misaligned or have faulty bearings, which also cause belt slippage. While faulty pulleys can be fixed easily, faulty bearings will most definitely have to be replaced.
  • Sometimes the belt keeps coming off because of oil slippage or a misaligned belt, which have to be fixed as soon as possible.
  • Other times, even accumulation of dirt on the deck or the belt causes the belt to split repeatedly.
  • Make sure to keep the lawn mower’s deck in perfect condition to prevent dust from sticking to the belt.

As someone who is seriously invested in lawn care, you will eventually have to deal with a slipping mower belt sooner or later. Our extensive guide discusses all the reasons why this might happen and helps you fix the problem immediately.

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