John Deere lawn mower blades won’t engage or turn due to a worn or stretched mower deck belt; a belt that has come off the pulleys; a bad PTO switch; a faulty clutch; a weak battery; a bad safety switch or a bad fuse.
Take all precautions to safely work on your mower. Remove the ignition key and spark plug wire. Wait for all parts to stop moving.
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Follow all safety instructions provided in your equipment operator’s manual before diagnosing, repairing, or operating. Consult a professional if you don’t have the skills, or knowledge or are not in the condition to perform the repair safely.
John Deere Mower Blades Won’t Turn On or Engage
Worn Deck Belt
When the mower blades won’t turn, check the mower deck belt. Over time the belt can wear and fail to turn the mower blades.
A worn or bad John Deere deck belt is one that has cracks, wear, fraying, or a shiny glazed appearance. A worn deck belt may also sit deep in the pulley grooves.
Replace a worn belt. Even if the belt isn’t the main reason why your blades won’t engage, you must replace it when it begins to show signs of wearing.
The belt gripping the pulleys affects blade speed. A fast blade speed is required to create suction under the deck to lift the grass and give it a nice even cut.
Belt Came Off the Pulleys
If the belt has fallen off the pulleys, it will no longer turn them to move the mower blades. In addition to a worn belt, look for a stretched belt, bad pulley, worn tensioner arm, or missing spring.
You can find a list of items that will cause the John Deere belt to keep falling off the mower deck here.
Worn Idler Tensioner Arm & Spring
You will find a tensioner arm and spring used to hold the idler pulleys inline. On most mower decks, the pulley will be on one side of the bracket and the spring will be on the other side.
The hole in the bracket where the spring is attached can become worn or the spring itself can become worn. This can cause the belt to become loose and vibrate off the pulleys.
Worn Pulley Bearing
You will find a bearing in each pulley. The bearing can wear so the pulley no longer sits parallel to the mower deck. The worn bearing will allow movement in the pulley so it wobbles.
One side of the pulley may be sitting higher off the deck than the other side. The extra movement in the pulley can cause the deck belt to roll off of the pulley.
Not only will movement indicate a bad bearing, but you can also find a failing bearing by rotating the pulley slowly by hand. Feel for restriction or listen for a bearing noise indicating the bearing is going bad.
Replace a pulley assembly where the bearing is found to be bad. You may be able to replace the bearings in some idler pulleys.
Faulty PTO Switch (Electric Clutch)
The PTO switch is usually a knob installed on the mower that allows voltage from the battery to power the clutch. When the switch fails, the blades won’t turn on.
Check for continuity in the switch. Replace a switch with a break in continuity.
The PTO (Power Take Off) clutch transfers power from the engine to the blades by engaging the drive belt. A clutch that is worn or faulty must be replaced when it fails to power the blades.
For more details on clutches, check out A Look into How Lawn Mower Clutches Work.
Worn Clutch Cable on a John Deere (Manual Clutch)
You will find a clutch lever and cable on a mower with a manual engagement clutch.
Check the condition of the clutch lever, cable, spring, bushings, and linkages to make sure the clutch is being engaged and the parts are not worn
Replace any worn parts.
A John Deere electric clutch uses power from the battery. When the battery is weak, it is unable to provide sufficient power to the clutch solenoid to engage the mower blades.
Check the voltage of the battery using a multimeter. A fully charged 12-volt battery should give you a reading of about 12.7 volts.
Charge the battery when you get a reading less than this. If your battery continues to die you can find common things that are causing this in 5 Things That Are Draining the Life of Your Lawn Mower Battery.
Charge a Battery: Use a battery charger to charge a battery. Before you continue, wear protective gear to protect your skin from electrical shock and protect your eyes. Follow these steps to charge your riding mower or zero-turn battery with a charger:
- Access the battery and terminals. You may need to use a screwdriver to uncover the battery. You will find the battery under the hood or under the seat. Do not remove the battery from the casing.
- Connect the battery charger cables beginning with the positive cable first. This is the red cable or the one with the plus sign. Place the cable on the positive battery terminal.
- Attach the negative cable to the negative battery terminal. This is the black cable or the one with the negative sign.
- Do not touch anything that doesn’t have a rubber coating to prevent electrocution.
- Set the charger’s voltage and amperage level to the desired level. The average volt level for lawn mower batteries is usually 12 volts. More amperage charges the battery faster. Start with two amps and work up to no more than 10 amps. A slow charge is best.
If you find the battery won’t hold a charge, you must replace it with a new one. You can find 12-volt lawn mower batteries at your local hardware or automotive store. You may also find batteries at your local lawn mower dealership.
Bring the old battery with you. Most places will charge you a core fee unless you provide them with your old battery. Core fees average $20.
Bad Safety Switch
Safety switches are put in place to add protection for the operator. One of these safety switches is the seat switch.
This switch is engaged when the operator is in the seat. When the seat switch is not engaged, the mower blades will not turn off.
For example, when I was younger, I mowed our family lawn with a John Deere lawn tractor. The ground wasn’t very smooth so every time I hit a bump, the mower deck would shut off because I would bounce off the seat and the seat switch would no longer be engaged.
When your seat switch is acting up and no longer recognizes the operator in the seat, the mower blades will fail to turn on.
Test the seat switch using a multimeter or you can temporarily bypass the safety switch to identify a bad switch. Do not operate a mower without the safety switch installed for your safety.
Always have safety switches installed and working on your equipment.
A fuse is used to protect the mower’s electrical system. When you aren’t getting power, you may have blown a fuse.
Replace a blown fuse with the same amperage fuse. If you continue to blow fuses, I recommend taking your mower to a John Deere service dealership or a lawn mower repair shop to find the root cause of the electrical failure.
Still Having Problems with Your John Deere Lawn Mower?
As a John Deere owner, you will encounter a variety of problems over the life of the equipment. These can include problems with starting, dying while mowing, vibrating, cutting unevenly, and not moving.
To help you identify the reasons your mower is having problems, I put together a handy guide to help you troubleshoot your mower. Check out Common John Deere Lawn Mower Problems and Solutions.