Whether you have an old mower, new mower, tractor mower, or zero-turn, you can run into the problem that the mower blades won’t disengage. I’ve run into this situation myself a couple of times, either after finishing a cut and wanting to turn the blades off or when trying to start my lawn mower and the blades are already engaged. After researching countless owner manuals and tinkering with my lawn mowers, I’ve discovered several possibilities why mower blades won’t disengage.
Why Won’t My Riding Mower Blades Disengage? (The Short Answer)
Firstly, a faulty clutch system caused by either a damaged clutch or broken switch and wiring could cause the lawn mower blades not to disengage. Secondly, the idler could have a damaged part in the mechanism, causing the idler pulley to stay engaged.
9 Potential Causes of Riding Mower Blades Not Disengaging
What type of mechanism does your lawn mower use to engage the blades? If you have a lever that mechanically moves cables and pulleys, you have an idler system. Whereas if you use an electronic switch, you have a clutch system.
What Can Go Wrong With an Idler System
Taking a Craftsman LT Series Tractor or a Troy Bilt Pony Tractor as examples, these mowers use an idling system to engage the deck. The system consists of the engagement lever, cable, mounting points, spring, arm, and pulley. Any faulty part of the system can cause the mower blade not to disengage. Consequently, the system can fail in the “on” position. Let’s break down what each component does and what problems they can cause.
Engagement Lever Might be Loose
The engagement lever is the device you use to activate and deactivate the blades. The lever should be securely fixed to the lawn mower’s frame with the idler cable in place. The lever’s function is to extend and contract the attached cable/rod to engage and disengage the idler arm and pulley. If the lever isn’t functioning correctly, it may be unable to disengage the blades. If anything looks loose or broken, you’ll need to carry out a repair.
Idler Cable & Idler Rod Could be Stretched or Bent
When selecting to engage the blades, the idler cable transfers the motion of the lever to the idler arm. You’ll see that the cable is attached and mounted at both ends. The inner cable is attached to the lever and idler arm, whereas the outer cable sleeve is attached at both ends, usually to the mounting structures. Similar to the cable, you may find that you have a solid rod that attaches to the lever and the idler arm.
Again, check to see if this is correctly connected and not damaged. If it is, it could get caught up and restrict movement. Finally, both cables and rods have adjustments. If incorrectly set, it could stop the idler arm from returning. You should see that the mechanism is activated by pulling the lever backward and forwards. A repair or adjustment is required if anything looks out of place.
Idler Arm Could Be Worn Down
You’ll usually find the idler arm attached to the lawn mower deck. Connected to the arm is the idle pulley. This pulley completes the circuit of the belt to run the blades. Engage the idler using the lever and observe the action. If you disengage the blades and the idler arm doesn’t return, you’ll know there is a problem.
With extended use, the idler arm can become worn. As a result, it’s very common for a groove to appear in the arm that causes it to get caught up. So first, check to see if the idler arm is bent or broken, then check if it’s worn down and has a groove. After that, you’ll have to replace or fix the part depending on the damage or wear.
Mounting Points Could Have taken a Knock
One of the quickest tasks in diagnosing why your mower blades won’t disengage is checking the mounting points. First, look around the lawn mower at all the places where the mechanism is attached. Next, check for any bent or broken area causing the idler to get stuck. If there is, you’ll be getting out your tools.
Idler Return Spring Could be Missing
The spring is designed to keep the belt’s idler arm and pulley clear when the blades are disengaged. This spring should be connected to the idler arm and the deck. Additionally, it should be able to recoil. Hopefully, the spring is as it should be, not stretched or bent.
In the worst-case scenario, you may find the spring is missing entirely. If you diagnose any suspicious problems or it’s gone walkies, you’ll have to make a trip down to the parts supplier.
There’s a chance that your particular mower may have a spring attached to the end of the idler cable. If this is the case, check it the same way you would a stand-alone spring, making sure it’s functioning correctly.
Pulley May Have Got Damaged
Finally, you’ll need to inspect the pulley. The pulley is the final part of the idler system before tension is given to the belt. Try to give this a spin and a shake to see that it’s working correctly. A seized pulley isn’t going to stop you from disengaging the idler, but if it’s bent and out of place, it could obstruct the idler’s arms movement and affect its ability to return.
In addition, some pulleys are adjustable on the mounting plate. Again, like a seized pulley, it’s not going to keep the blades from moving, but it can apply enough pressure to maintain contact with the belt to wear it down. So, just look out for this. If you find an issue with the pulley, you’ll need to reach for your wrenches.
What Can Go Wrong With a Clutch System
Tractors such as the John Deere Z Series and Husqvarna TS Series use clutches to engage their blades. These lawn mowers use a centrifugal electromagnetic clutch using voltage provided by the mower’s electrical system. This clutch can fail by seizing due to wear or corrosion. Additionally, an engagement switch can break internally, resulting in the control remaining in the “ON” position regardless of where it’s set. Another possibility could be something at fault with the cable to the switch. If the cable has a short circuit, it will remain energized and stay in the “ON” position, causing the clutch to be continuously engaged.
Last but not least, there is the clutch brake. The brake stops the clutch pulley from turning once the blades are disengaged. If this is worn or damaged, the blades continue spinning for a period until momentum is lost. This won’t stop the mower blades from disengaging, but it has similar symptoms of a failing clutch, so it’s good to look out for.
Let’s investigate these parts and better understand how to diagnose what could be going on.
Blade Engagement Switch Broken & Electrical Cables Could Have a Short
Let’s start by diagnosing if there is a problem with the electrical system as a whole.
Like with most mowers, if not all, safety features stop the blades if the mower isn’t being used correctly. The primary safety feature is a safety switch under the seat. You will probably notice that the mower will cut off if you get off a mower with the blades running or if the brake isn’t applied.
So, take a seat on the lawn mower seat with the brake on. Give the key a turn to ON, then OFF. If there is a switch or electrical cabling fault, the clutch will engage as soon as it receives power by turning the key. You will be able to hear a clicking sound coming from the clutch as it engages and disengages. If you hear the clutch as it engages and disengages, you need to investigate whether it’s the switch or the cable at fault.
Testing if it’s the Switch that’s Gone Bad or the Wiring
With the ignition switch set to the “OFF” position, remove the connection for the switch.
You might need to remove the switch from the mower to do this. Once the switch is disconnected, wrap some electrical tape around the loose wires so they can’t touch. Now you can go ahead and switch the mower ON and then back OFF, remembering to be in your seat with the brake on and not starting the mower. If the clutch continues to come ON and OFF, you have located the fault in the wiring.
If it doesn’t, then the switch is at fault. To confirm the switch is at fault, you can test it with a multimeter by checking if power still runs through it when set to OFF. If power can still pass through when switched OFF, you’ll know the switch is at fault, and it’s time for a new one.
Checking if the Clutch is Burnt Out
When testing a clutch, it’s easiest to remove the deck belt. As a result, this will give you easy access to the clutch with the ability to turn it manually. Try turning the clutch pulley with the belt removed and the battery disconnected. With the battery disconnected, the clutch has no possibility of being energized, and it should move freely. If you find any restrictions or hear a bad sound, you’ll discover that your clutch has gone bad.
While down there, check to see that the clutch brake isn’t stuck. Again, this isn’t going to keep the blade from disengaging, but it will allow the blade to spin much longer once it is switched off, and you could get confused.
How to Fix a Riding Mower with a Blade that Won’t Disengage
We’ll delve into how to perform your repair now that you have diagnosed the cause. So, let’s run through all the necessary steps and tools, plus the parts you’ll have to get.
The first thing you will want to do is get the mower on some level ground. I’d suggest working in your garage or workshop. Then place some sturdy items against the tires so the mower can’t roll away. Anything heavy enough will do. Finally, remove the key or disconnect the battery. I’d also disconnect the battery to be extra safe.
Engagement Lever
Here you will have to remove the plastic surround on the mower that the lever passes through; a screwdriver should work fine for this. Just be careful with the paintwork. This is, of course, if you have a surround. Alternatively, you may be able to gain access from the backside and not have to worry about removing any surrounds or covers.
Now, with access to the lever mounting bolts, you’ll be able to tighten them up if they have come loose. With the lever mounted correctly, give the mechanism a try. You should be able to use the lever with free movement and without hitting the lawn mower’s body.
Tools
- Screwdriver pry tool
- Socket Set
Idler Cable & Idler Rod
Idler cables come in two types: a cable or a cable with a spring attached. Let’s see how you can repair each of them.
Idler Cable Without Spring Attached
First, start by removing the cable clips. Each end of the cable is mounted using a clip to keep it in place. Take a set of pliers and remove the clips. You’ll find the first clip attached to the lever and the other attached to the deck.
Once these are removed, you should be able to unclip the cable. Then, follow along the cable and remove any clip that holds the cable to the lawn mower’s structure. These are just clips that keep the cable from dangling around. With all the mounting clips removed, you should now be able to remove the cable from the mower.
Once the cable is removed, you can check that the idler arm can move. It will be a little challenging to move as it will have the idler spring attached, but you should be able to move it back and forwards.
Now take your replacement cable and install it by reversing the previous steps. Install the ends of the cable first, then attach the mounting clips. Once the cable is in place, try to engage the blades. If you find the lever is either engaging too much or disengaging too much, then use the adjustment point on the cable until you find a happy medium.
Idler Cable With Spring Attached
If you need to replace an idler cable with a spring attached, you will follow the same process as before, just that this time one end of the cable will have a spring attached. When installing this cable, install the lever end before the spring. You will find it much easier doing it this way. Then, when you have the cable installed, you can apply any adjustment you need.
Once complete, you can test the idler system and confirm the repair is done.
Tools & Parts
- Pliers
- Screwdriver/Socket set to remove clips.
- New cable
Idler Rod
An idler rod does the same job as the idler cable. The difference is that they are made of a solid piece of metal. The idler rod is mounted to the mechanism with nuts. These nuts will need to be removed from each end to allow you to remove the rod.
Take a wrench and locate your idler rod. Start by removing the outer nut from each end of the rod. You may find either a double nut or a nut with an internal plastic washer. Whichever you discover, you’ll need to remove all of them. Now you can remove the idler rod.
You will notice that your old idler rod still has nuts and washers. These will need to be removed and placed onto the new rod. First, put both idler rods inline with one another and transfer the position of the nuts onto the new rod. You need to ensure that these are installed at the exact location on the new rod since they are used as the adjustment of the idler. I like to use some electrical tape to mark the positions on the new rod as this tends to stay in place and doesn’t rub off as a marker pen does.
Transfer the bolts and washers onto the new rod inline will your markings and install the rod into the idler systems. With it in place, you can go ahead and install the remaining nuts and washers. Like when installing an idler cable, you can check the adjustment by engaging and disengaging the lever.
If you need to adjust, move the bolts up or down the rod. Once you find the perfect spot, tighten up all the bolts nice and tight.
Tools & Parts
- Wrenches
- New Idler Rod
Idler Arm
You need to remove the lawn mower’s deck to carry out any work on the idler arm. Start by removing the belt. With the belt removed, you will need to remove the deck. The deck is clipped onto mounting points on the lifting mechanism, usually with four pins. Start by lowering the deck to its lowest setting, then locate the pins. Grab a set of pliers and remove the pins. Once the pins are removed, you can lift off each mounting bracket. Be very careful at this point, as these are holding the deck up.
Once the brackets are removed, the deck should be on the floor with just maybe one more mount left at the front of the mower. Depending on your lawn mower, this may be bolted on, or it could be resting on hooks. If you need to reach for your wrenches, then do so. Finally, you’ll need to remove either the idler cable or the idler rod. So, either unclip the idler cable or remove the nuts on the idler rod. Finally, the deck should be free from the cable/rod, belt, and mounting brackets. Once you confirm this, you can pull the deck out from the side of the lawn mower.
Now it’s time to remove the idler from the deck. Thankfully, this isn’t difficult. Take a screwdriver and remove the idler spring. You should be able to just pop this off. Then, take a wrench and remove the bolt that holds the arm in place. With the idler arm removed, you should be able to see where there has been a groove worn into the surface. Depending on how much of a groove has been worn down, you might be able to file the groove out. I recommend replacing it if it’s a deep groove, say over ¼ inch. Whichever route you choose to take, you’ll need to remove the pulley. Take your wrenches and remove the pulley so it can be used later. Just be aware that a stuck lawn mower pulley is not uncommon and they can sometimes take a bit of “persuading” to come off. I’m speaking from personal experience here.
Tools
- Wrenches
- Pliers
Repairing the Idler Arm & Pulley
If you have chosen to repair the idler arm, place it in a vice with the groove facing upwards. Take a metal file or an angle grinder and work out the groove. Ensure that you form a nice flat surface, not a dip when working out the groove. A dip will cause the idler to get hung up again. Once you have completed your filing, check that you haven’t removed so much metal that the idler arm has lost its strength. I’ve seen these snap before, even without filing any metal off. If you have any concerns, replace the part with a new one.
With either your repaired or replacement idler arm in hand, you can go ahead and install the pulley and the idler arm to the deck. Before you install the pulley, check it. This is the perfect time to change it if you see that it’s worn or damaged.
Once installed, move the arm back and forth to check it’s moving freely. This time the arm should no longer be getting caught up as there is no longer a groove. With the repair complete, you can reinstall the deck and belt and give the mechanism another try. You should be ready to start cutting if everything was done correctly.
Tools & Parts
- Wrenches
- Socket Set
- Metal File/Angle Grinder
- Vice
- New Idler Arm
Mounting Points
If you happen to have a damaged mounting point obstructing the idler system’s movement, you’ll need to straighten them out. Your approach to the repair can vary depending on the severity of the damage and the thickness of the metal.
If it’s a lightweight mount, you might be able to straighten it out with a pair of grips. A hammer could be necessary if it’s something more substantial. Anytime I need to use a hammer, I like to place a piece of wood against the mount first. Banging with a hammer can misshape what you’re trying to fix. So, approach with caution.
A word of warning – the heavier mounts are sometimes welded to the mower, so you have to be careful. You may remove the bracket and break the weld if you bang too hard. Therefore avoid any continuous backward and forward striking against the weld. Straighten the mount and test the idler system using your tools. If you need to do this multiple times, just repeat the process.
Tools
- Grips
- Wooden Block
- Hammer
Idler Return Spring
Idler springs are hooked onto the idler arm and then to the deck. Start by disengaging the blades. Since the spring isn’t working correctly, you may need to move these parts by hand. With a pair of pliers, you can lift the spring off of the deck. Just be careful that it doesn’t go flying.
If your spring is already gone, you don’t have to worry about this. Take a new spring, hook it to the idler arm, and then onto the deck. I would suggest using your pliers. With the new spring in place, give the mechanism a try. The new spring should retract the idler arm, and you should be good to go.
Tools
- Pliers
- New Idler Spring
Blade Engagement Switch
If you found the switch faulty during your diagnosis, you’ll need to replace it with a new one. Then, all you need to do is connect the new switch and fix it back into place. Before connecting the switch, check that the wire connectors are in good shape. I like to give them a quick rub with a tiny metal file to remove any corrosion and dirt.
You always want to get a good strong connection. Then, you can reconnect the battery and test your repair with the new switch installed.
Tools & Parts
- Pliers
- Replacement Switch
Electrical Cables
Once you have located your damaged cable, you need to decide if it needs to be replaced or rejoined. If the cable has been pinched, a join will be fine, but if it’s damaged over a few inches, you’ll need to replace the section. What you don’t want to be doing is making a repair that puts tension on the cables.
First, disconnect the battery. Then cut out the damaged section of wiring. If you are unsure of cable sizing, it’s best to take the removed section to the store and have a professional tell you the gauge.
Then, prepare the ends of the cable that are left in place by removing a ½ inch of the insulation. Slide on a heat shrink tube that is sized correctly for your connector. I like to insulate each connection separately and then insulate both connections together. So you’ll need two different size heat-shrink insulator sleeves.
With the sleeves in place, take a butt connector and insert the exposed cables, ensuring you have the correct wires, and crimp the connector. I find that a crimping tool works much better than any other tool. Other tools, like pliers, just don’t give the connector the bight it needs, and the connector ends up falling off. If you need to extend the wires, follow the same process, but use your additional wire between the connection.
With the connection complete, you need to heat the heat shrink tubing to mold it around your connection. I have a heat gun for this, but you could use a hairdryer. I wouldn’t use a lighter or direct flame though.
Finally, protect the repair with some flexible, split conduit. You’ll see this is the same product the manufacturers used to protect the cable in the first place. Now you can reconnect the battery and test your completed repair. You should be able to hear the clutch engage and disengage with the switch.
Tools & Parts
Wire Cutters
Crimping Tool
Heat Gun
Additional Electrical Wire
Butt Crimp Connector
Heat Shrink Sleeving x2 Sizes
Split Conduit
Clutch
Good news: I saved the best till last. Changing a clutch can either be straightforward, or it can be a problem. This depends on how bad the clutch is. It could be stuck if it’s burned out and became extremely hot. On the other hand, if you caught it early, then it should come off fairly simply.
Start by disconnecting the battery and the clutch connector on the clutch. Then, remove the belts. If you’re working on a mower with a hydrostatic drive, you might need to remove both the deck and drive belts for access.
Remove the cover from the flywheel cover located on the top of the engine to expose the flywheel nut. Then remove the center mounting nut/bolt from the clutch while holding the flywheel nut. I would get some help with this as doing it by yourself will be very difficult. Once you remove the clutch mounting nut/bolt, the clutch should drop out of place.
This is where things can get tricky. The clutch more than likely isn’t going to fall out of place. Instead, it’s going to need some help. A clutch puller tool is the safest way to remove a stuck clutch without damaging your engine. Start by spraying a penetrating oil or lubricant to the center hole and allow it to soak in.
Next, take your clutch puller and tighten it until the clutch comes away from the mount. If you have difficulty removing the clutch, you may need professional help. Definitely don’t reach for your hammer. If the clutch became very hot, it could be nearly impossible for you to remove. A professional will probably have to use a heat torch to remove it, and this should be left to the experts.
Once the clutch is removed, the new one can be installed. Take your new clutch and align it to the key on the engine shaft and to the bushing on the pulley. The shaft isn’t completely round, nor is the pulley. These parts need to be aligned to fit together. Once aligned, you can slide on the clutch a little bit, and then you’ll need to align the mounting slot on the frame with the clutch. Once everything is aligned, you can slide the clutch on completely.
Follow this by inserting the bolt/nut and tighten it up. Again, get your helper to hold the flywheel nut and tighten the clutch fully. With the clutch installed, you can go ahead and connect the clutch power, install the belts and replace the flywheel cover. Finally, reconnect the battery, and you’re done.
Tools & Parts
- Screwdriver
- Wrenches
- Socket Set
- Clutch Puller
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