Mower belt keeps breaking. 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.”

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.

Zero Turn Mower Belt Keeps Slipping from Guide

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.

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.

Bearings

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.

STOP Your Mower BELT From Coming Off (HERE’S HOW)

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.

Tools

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!

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.

And the best part. it’s free!

Reasons Craftsman Riding Mower Deck Belt Keeps Coming Off

Nothing is more aggravating than having to halt mowing in the middle just because your Craftsman deck belt keeps falling off. But what drives the Craftsman mower belt to keep coming off?

4 most common causes behind such a commotion are:

• Wrong size/type or incorrect installation of Deck Belt.
• Improper tension on the Blades or Belt.
• The Deck Wheels or Pulleys are misaligned.
• wear and tear on the Belt or Pulleys.

Aside from the causes mentioned, other potential conditions can cause your Craftsman Riding mower deck belt to come off. Hence, keep reading to find out more about them and how to solve the problem.

6 Additional Reasons Why Craftsman Deck Belt Keeps Coming Off:

• Bent or Damaged Deck Belt Keeper
• Loose, Stretched, or Shredded Deck Belt
• Damaged Bearings or Spindle Housings
• Worn-out Idler Tensioner Bracket or Spring
• Built-up Debris, Oil, or Rust on Your mower Deck Belt

Things to Consider If Your Craftsman Riding Mower Deck Belt Keeps Coming Off:

Immediately check the following fault areas to find out the exact problem_

Choose the Correct Deck Belt Size/Type Installed it Accordingly:

You can always get cheaper aftermarket parts whenever you need to replace the current one. But these aftermarket options cannot beat the quality of an OEM belt.

Because OEM options last longer and minimize safety concerns.

Make sure that the belt you select can withstand the stress exerted by the mower.

Standard V-belts are usually good. However, depending on the model of your mower, more options are available.

To select the right size of deck belt for your Craftsman, you need to know the make and model number of your mower, which is available in your user manual.

If you do not have the user manual, check on the deckle under the mower hood, you will see the part number there.

Or use a belt measuring tool to measure the current deck belt to choose the new one.

Also, make sure that you have installed it correctly.

Look For Improper Tension on the Deck Belt

If the deck belt on your Craftsman riding mower is not properly tensioned, it will come off during mowing.

Once you are sure that you need to adjust the belt tension to prevent it from slipping, inspect the swing arm first.

Then, disengage the blades to adjust the belt tension correctly.

Note: before you start performing the adjustment make sure that no cracks or big chunks are missing from the belt. Otherwise, you must replace the belt.

Check For Misalignment

If the deck, deck wheels, or pulley is not aligned correctly, the Craftsman deck belt will not stay in place and keep coming off unless you adjust the alignments as needed.

The mower deck:

If the deck has a wrong alignment, you need to adjust the blade height and level to adjust the alignment.

• Set the blade at its highest setting.
• Measure 3 inches from the ground in four separate places around the outside of the mower deck.
• Compare those measurements.
• If they are not similar, adjust either one or both front and rear adjustment screws until they become equal.

Mower deck wheels:

Follow the below instructions to align the deck wheels accurately_

• Park your Craftsman on a level surface and turn off the engine.
• Lift the mower hood to locate the adjustment screws for each wheel.
• Turn each screw clockwise to increase or decrease its height until all four wheels look leveled from all angles.
• Once you have achieved the desired alignment of the wheels, tighten down all adjustment screws securely.

Follow the below instructions to align the misaligned pulley_

• Lift the mower hood to locate the pulley.
• Check whether all tension springs or idler arm components are tensioned properly or need adjustment.
• Loosen their mounting bolts slightly to adjust them accordingly if needed.
• Make sure all components are securely tightened.
• Check the Condition of the Deck Belt Keeper:

The small rod-shaped poles sitting next to the pulley on your Craftsman riding mower are known as the belt keepers.

These keepers mainly guide the belt to keep it in place.

But these keepers might bend outward or move out of place and allow the deck belt to jump out of the pulley due to excess slack in the belt or when the belt snaps.

So, take the pulley off and bend this tab to get the keeper closer to the pulley.

Check and do the same thing to confirm that all the keepers are as close to the engine pulley as possible.

If any belt keepers have turned too bad to fix like that, replace them.

Make sure That the Deck Belt Is in Good Condition

Your Craftsman deck belt tends to come off when it has become loose. It can become loose when the belt has worn out or stretched over time.

You can also notice shredded marks on the belt. When the belt rubs against a bracket or your belt keepers, it leaves shredded marks.

It occurs due to improper adjustment of the brackets and belt keepers.

If your deck belt has become loose due to wear and tear or stretching, you should replace it. If you have a shredded belt, determine where the markings are coming from and correctly adjust that location to avoid rubbing.

Inspect the Idler Tensioner Bracket or Spring

Your deck belt can also keep falling from its position due to a worn-out idler tensioner bracket or spring.

Therefore, visually inspect and look for any signs of corrosion, cracking, or other hints that indicate either the tensioner bracket or the spring is worn.

Also, test the tensioner by pushing on it, and if there is any excess play or movement, it’s time to replace the idler tensioner bracket or spring.

Inspect the Bearings or Spindle Housings

You also need to check the bearings located in the idler pulley and spindle housing because if one of those bearings fails, it will gradually cause the belt to fall off.

If the pulleys are rotating straight rather than flat, one of the bearings has failed.

Similarly, follow this easy tutorial to check the bearings located in the spindle and replace them if necessary.

Maintaining a beautiful lawn can be a daunting task, especially if you lack the appropriate know-how and tools to handle the challenges that may crop up. Fortunately, LawnAsk is here to offer you an all-encompassing resource that covers everything you need to know about lawn care.

Recent Posts

When to Replace Lawn Mower Belt (Drive Deck Belts)

The lawnmower belt(s) is the main component that helps drive the power from the engine to drive the propeller which cuts the grass.

Over time, general wear and tear will occur and the belt(s) will eventually wear out and potentially break or not be able to cut your grass as efficiently.

But when is the best time to replace it? We will also review how long they last and ways to make the belt last longer whether it be on a push, self-propelled or riding lawn mower.

When to Replace Lawn Mower Belt?

There are two different types of belts; a drive and deck belt. The deck belt is the main belt which helps drive the propeller to cut the grass. The drive belt is what helps move the mower on its own (self propelled or riding mowers).

If you have a push lawnmower (electric or petrol) this will only have a deck belt. The belt should last the lifetime of a typical lawn mower (8-10 years, if used in ideal conditions and properly maintained). However if in the situation the deck belt needs to be replaced you will find out the propeller doesn’t run and not cut the grass where this is the most obvious symptom (other symptoms are explained later).

If you have a self-propelled or riding mower, you will find an additional belt which is the drive belt. As it states in the name, this helps drive the wheels of the mower to move and will help drive the other components for the deck belt. These belts last between 3-4 years (again depends on the amount of use of the lawnmower) and should be replaced within this time period, but of course if the mower is still running as it should, the replacement will be put off but there are various signs and symptoms to indicate if the belt should be replaced which is explained in the next section.

How to tell if a mower belt is too worn?

There are easy tell-tale signs which show a worn mower belt, but how do you tell the difference between a worn (still ok to use for a fair few sessions) or a very worn belt (will most likely break in the next one or two sessions).

The best way to check is to visually inspect the belt and the upcoming signs are of belts which need replacing.

One obvious sign is whether the belt is shiny and completely flat with little to no ridges or bumps (depending on belt design) on the surface which fits into the grooves of the pulley system. Then this is the obvious sign of a worn belt that needs replacing.

Other signs are cracks in the actual belt itself. If you bend the belt the other way from its natural position and it splits open then the belt has been cracked and it won’t be long until it snaps.

If you find the belt quite slack between each pulley, this is also a sign of old age or wear and tear. This will not efficiently run the mower and will be more prone to slipping when mower is on. Don’t get confused if you have a feature to un-tension the belt on the mower which is normal depending on the design of your mower.

If it is particularly difficult to access the belt or you want a quick way to notice the belt is too worn, keep particular attention to your next mowing session. Some signs may include:

General signs:

• Mower stops/stutters at times (as it has lost traction to drive the wheels)
• Excessive vibration through the mower

When to replace self-propelled lawn mower belt

One key design of the self-propelled lawn mower is that it helps move the mower along which prevents you from having to push the mower, only requiring you to steer it in the direction of where you want to cut your grass. If you suddenly feel that you need to exert more force into pushing the mower or if the drive is slower than usual it is time to replace the drive belt. The last thing you want is the belt to snap as this can cause problems elsewhere if it gets caught or hits other components.

When to replace riding lawn mower belt

Similarly to a self-propelled lawn mower, you will need to replace the drive belt from time to time, you will find similar symptoms to the self propelled lawn mower where the mower may not drive very well, the belt may slip and mower may feel it is stuttering while driving.

Why does my lawn mower belt keep breaking?

If you have recently broken your mower belt or just replaced your mower belt and the belt has broken in no time, there are reasons why this has happened.

One common problem is excessive cut grass clippings on the deck. These clippings can get caught in between the pulleys which the belts are directly driving. This will cause unwanted additional tension to belts and may cause stretching to the belt which will loosen and then more grass clippings could get caught and would eventually snap the belt.

Another problem could be an oil leak within the engine, this will simply destroy the belt. If you have recently replaced a belt and it has broken with little use of the mower, you should check for oil leaks.

Broken or faulty pulleys can also cause broken belts. The pulley is meant to spin freely as the belt gets pulled around it. If the pulley is not spinning freely, uneven or excessive friction will occur on the belt and consequently wear it out quicker. If the pulley doesn’t look broken it is worth checking the bearings as these may be worn and may need replacing.

If you have recently replaced your belts, it is important to tension the belt correctly according to your owner’s manual. If it has been over-tensioned, this will cause excessive strain on the belt when in use and will break quicker than usual. Misalignment of the belt to the sheave (groove(s) of the pulley) can also cause excessive wear, so make sure the belt grooves are aligned properly within the pulley, an easy way to check is if you spin one pulley the other pulley that the belt is wrapped around will move at the same time and frequency.

Checking the type of belt used in your mower is important especially if you are going away from what is stated in the owner’s manual. Factors such as the material, type of the belt and lengths are important and vital to ensure the belt lasts the intended lifetime they were made for. If you have purchased a belt that is not recommended within your owner manual but the design and lengths of the belt are correct the material is likely not to be the same as the original and most probably won’t be able to take the strain of the mower over its intended life.

It is worth noting some mowers only allow you to use the OEM (original equipment manufacturer) components, so no matter what belt you buy even if you match all the specifications of the OEM belt it may still not last as long as intended. However if in the case you can use other belts, use a belt which is made from Kevlar (often used in bulletproof vests), this is far more long lasting than the regular rubber reinforced with polyester cord belts. Although this is a more expensive option it might be worth using if it is particularly hard to change the belts depending on your mowers design.

How to keep lawn mower belt running for longer?

If you want to keep the replacement of the belts to a minimum these common procedures and guidance will keep the belt running for longer:

• Remove grass clippings at the end of every session (check the deck and in between the pulley belt)
• Use the mower for no longer than the recommended time, excessive heat will cause unnecessary wear the belt and weaken it over time
• Check the tension of the belt as often as possible and adjust where necessary as according to your manual
• Use the mower in the ideal conditions (dry and not completely over grown grass), if you are using it in conditions that are not ideal (wet and completely overgrown grass) it will wear the belt far quicker, if you do have very overgrown grass, trim it down first and complete the lawn in 2 sessions

The advice above is generic and covers all the mowers but of course refer to your owner’s manual and the recommendations of maintaining the mower as there may be extra/special features which may not be on regular mower that may need special attention which may affect the belts if not properly maintained.

Related Questions.

Do you have to remove mower deck to replace belt?

This will depend on the type of mower you have. On a riding mower the belt should be accessible at the deck when it has been lowered to its lowest position or if you can lift the mower to access underneath the deck. However, if you have a self-propelled or push mower, this may be more difficult as this is often covered and protected by casing, so yes you may have to remove the deck to replace the belt. A drive belt is more difficult to replace and you are more likely to need to remove the mower deck on older models. Newer models may be designed so that the drive and deck belts are accessible once the cutting deck has been lowered into the lowest position. Again with any maintenance ,check your owner’s manual.

How many belts does a riding lawn mower have?

Some texts state that a riding lawn mower will have 2 belts (drive and deck belt) whereas some refer to 3 belts (Power Take-off Belt (PTO) or Power clutch belt, Arbor belt and Drive belt). The PTO and Arbor belt is often referred to as the ‘deck belt’ as these are found within the deck which help drives the cutting propellers. These are different belts which is found in the same area but differ in lengths and use in the actual lawn mower. It is important to check your owner’s manual to ensure you differentiate between the two otherwise the mower won’t run as it should.

Why Belt Keeps Coming Off Riding Mower

The belt on your mowing deck is a crucial component that must work correctly to enable your lawnmower to operate.

Unfortunately, the belt can fail, leaving the mower unable to drive the blades and cut grass. One such bothersome belt problem is when it keeps coming off.

Whenever this happens, it disconnects the blades from the crankshaft, making them unable to turn.

Thankfully, you can fix most of the reasons why the belt keeps coming off riding mower without the help of a technician.

This article discusses nine problems that can cause your mower’s belt to come off and how you can address each problem.

Why Belt Keeps Coming Off Riding Mower

A lawnmower belt may keep coming off if the belt keeper is crooked or damaged or due to bent pulleys or bad bearings. Using the wrong mowing belt or worn-out belt can also cause the problem. The other common culprits include accumulated debris and incorrect belt routing.

When the belt on your mower keeps coming off, any one or more of these problems can be responsible.

Knowing what to look for and how to diagnose the problem can help you identify and fix the issue.

Before troubleshooting the problem with your mower, always ensure your safety first. Wear eye protection and protective gloves.

Next, pull out the spark plug wires and ground them against your engine to keep the motor from accidentally starting while you are working.

Once that is done, proceed based on the problem you are addressing out of the following nice:

Damaged or Bent Belt Keeper

The belt on your mower goes around a system of pulleys, each with belt keepers at specific locations around it to help maintain the belt in position.

If these belt keepers or belt guides become crooked, they may not perform their role properly.

As a result, the belt may come off the pulley and drop onto the deck while raising and lowering the deck.

The belt keeper is supposed to lock the belt in place, but a crooked one allows the belt some space to pass through and fall off the pulley.

You must fix or straighten the crooked keeper or belt guide to stop the mower belt from falling off.

What to do

Closely examine the belt keepers around each pulley on your deck for any signs of crookedness. If any keeper is bent away from the pulley, it may be the point where the belt falls off.

You will likely need to unscrew the bolt holding the pulley and remove the pulley to straighten the belt keeper before reinstalling the pulley.

While straightening a crooked keeper, ensure you do not bring it too close to the pulley so that it prevents the pulley from rotating freely.

Ideally, the rod should sit about 1/8 to ¼ inches from the pulley.

Accumulated Debris Under the Pulleys and Tensioners

Over time, grass, wood chips, twigs, and stones may form a mass of debris jammed in the space beneath the tensioners or in the pulley grooves.

When this happens, the accumulated debris competes for space with the belt. As the belt moves, the debris may push it out of place, forcing it to fall off the mower’s pulleys system.

In serious cases, the dirt and debris can nip the belt, causing it to break and fall off.

Solution

If accumulated dirt and debris under your mower dislodges the belt from its track, you must remove the buildup to stop the problem from occurring.

After that, you can prevent similar future buildups by cleaning the mower deck and the area around the pulleys system after every mowing session.

Removing solid particles and pieces from this area once you finish mowing will go a long way in preventing them from accumulating and creating a buildup that displaces the mower belt in the future.

Worn or Slacked Mower Belt

After using your mower for a while, the belt may become worn out or loose.

Worn mower belts may lose entire fragments, remaining with thin sections that can easily pass through the small space between the belt keepers and the pulleys and fall off.

A worn-out belt may also be slacked and stretched, losing its ability to maintain its position within the pulley grooves.

When slack, the riding mower belt can easily slip from time to time. Additionally, it can also create friction that could endanger your machine.

What to do

Inspect the belt for any signs of fraying, slackness, separation from the rest of the pulley assembly, or cracks.

If the belt is old and frayed, you should see the damaged parts or looseness if it has lost the required tension.

The only solution for a damaged mower belt is to replace OEM belt with a new one.

Incorrect Belt or Belt Size

The belt assembly and track are designed to fit a specific belt. Using the wrong belt would mean a mismatch that could create issues.

For instance, the wrong belt may be too long, resulting in slackness. As already mentioned, looseness endangers your mower and may lead to slipping off of the belt as the mower runs.

The wrong belt may also be too small, allowing it to pass through the small space between the pulley and the belt keepers.

These problems can cause the belt to fall off occasionally while mowing or lowering and raising the deck.

Possible fix

When replacing the belt on your mower, check your lawn mower model number and order the correct belt with matching specifications or dimensions.

Without checking these details, you could end up with the wrong belt that causes problems for your mower.

If the wrong belt is the problem, check your mower’s details and order the correct belt size to resolve the issue.

Once you have the right belt, fit it out and try running the mower to see if the problem is solved.

Damaged Bearings in the Spindle Housings

The spindles on your lawn mower transfer the engine’s rotational force to the blade through the system of pulleys on the mower.

The engine rotates the pulley on one end of the spindle, which spins the blade on the other end. Inside the spindle housing assembly are bearings that enable this high-torque, high-speed process.

If these bearings get damaged, they can wobble and cause the belt to slip off while operating.

You can tell if the bearings are damaged from the excessive vibration the spindle will create while rotating.

What to do

Examine the idler pulleys on your mower, feeling them with your hands to see if they are firm and parallel to the deck. The spindle pulley should run flat and parallel to the deck surface.

If the pulley is angled differently, it may be the reason your deck belt starts to come off. Ensure you wear sturdy leather gloves when approaching this part.

Rock the mower blade up and down while listening in for any knocking sounds to tell whether the spindle housing has damaged bearings.

If movement is inside the spindle housing, disassemble it and inspect for damaged components.

Replace only the bearing if the housing is unsealed. However, if it is sealed, replace the entire spindle housing.

Misalignment or Incorrect Belt Routing

Looping the belt incorrectly around the pulleys can cause problems leading to its coming off the assembly.

What to do

When taking off your belt to service the deck, consider taking pictures before unlooping the belt to ensure you get it correctly when returning the belt.

Also, ensure the belt goes through all the belt guides. Looping the belt incorrectly or failing to pass it through all the belt guides may keep it out of place, letting it off the pulleys.

Improperly Mounted Deck

The deck carries the pulley assembly. It needs to be mounted correctly to stay balanced. Otherwise, it may create problems when engaging the blades.

An off-balance mower deck may affect the belt orientation, potentially causing it to fall off when raising or lowering it.

What to do

You can fix this problem by checking how the mowing deck hangs. Refer to your owner’s manual for the correct way of mounting the deck.

If anything is off, correct it to ensure the deck is mounted properly. This may include replacing any missing parts likely to keep the deck from being balanced.

Bent or Damaged Belt Pulleys

Belt pulleys should spin freely if they are sound. If any is bent, it can affect the blade’s movement, allowing it to slip off.

Solution

Unloop the belt and check the deck for damaged or bent pulleys by rotating and inspecting each.

Try using a hammer to straighten any bent pulleys or replace them if they are in bad shape.

Torn Bracket/pulley Plate

Sometimes the pulleys may be okay, but the bracket on which they are mounted is not.

Over time, the plate or bracket holding the pulleys can get torn, affecting the belt orientation and potentially causing it to slip off.

Solution

Check the idler tensioner bracket for any noticeable damage and weld any split parts likely to cause the belt to slip off its track. You could also replace it if it is badly damaged.

Why Specific Mower Models Belts Keep Coming Off

Why Craftsman riding mower deck belt keeps coming off

Craftsman riding mowers may keep coming off due to a damaged, worn, or stretched belt. The problem can also occur due to bent belt keepers or damaged pulleys.

Why Troy Bilt deck belt keeps coming off

Troy Bilt deck belt can keep coming off if the belt is damaged, stretched, or worn out. They can also slip off the idler pulley system due to faulty spindle bearings in the spindle housing or bent pulleys.

Husqvarna mower deck belt keeps coming off

If your Husqvarna mower deck belt keeps coming off, the mower may have damaged pulleys, belt keepers, and bearings in the spindle housing.

John Deere mower deck belt keeps coming off

John Deere mower deck belt may keep coming off if the lawnmower has an incorrect or shredded belt on its deck. Damaged pulleys or bearings in the spindle housing can also cause the problem.

Zero-turn drive belt keeps coming off

Your zero-turn drive belt can keep coming off if the bracket holding the pulleys on the deck is split or torn. The problem can also occur if the belt keepers are crooked or the pulleys are damaged.

MTD deck belt keeps coming off

MTD deck belts can slip off the pulleys due to bent belt keepers, damaged pulleys, or faulty bearings in the spindle assembly housing.

Why does my Serpentine belt keep coming off?

The reasons your Serpentine belt keeps coming off may include stretched lawn mower belt, incorrect mower belt, damaged pulleys, or bent belt keepers.

What causes the belt to come off of Cub Cadet Mower

The deck belt may come off Cub Cadet Mower due to damaged pulleys, crooked belt keepers, an imbalanced deck, bad bearings in the spindle assembly housing, and incorrect belt looping.

How do I know if my lawn mower pulley is bad?

You can check if your lawnmower pulley is bad by spinning all the pulleys on deck one at a time. Good pulleys will spin freely, while the bad ones will have some play or resistance. You can also see signs of wear and damage inside any bad pulleys.

Final Thoughts

A mower belt that keeps falling off can waste a considerable amount of your time. Thankfully, you can fix most of these problems if you know where and what to look for.

This article provides a detailed account of the common problems likely to cause your mower belt to come off. It also suggests the solutions for each problem.

We hope this post helps you get your mower back up and running quickly. Let us know your thoughts in the Комментарии и мнения владельцев.

Rhys Charles

Rhys is a passionate landscaper, a self-proclaimed barbecue expert and the author of this site. He combines his lawnmowing expertise with his engineering background to teach you about how to not just take care of grass, but also the equipment you use.

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