The PTO clutch is an essential part for your lawn mower’s function. Without the clutch, or with a poorly functioning clutch, your riding mower will be nothing but a slow, one-seater vehicle. While this may be useful for teaching your teenage kid to drive, it will be useless for mowing the lawn. The clutch is needed to transfer power from the motor to the blades, so that you can cut grass! Luckily, it’s pretty easy to tell if you have a bad clutch. We will go over some ways to diagnose and fix lawn mower clutch problems here.
How to Spot Common Riding Lawn Mower Clutch Problems:
If you are activating your PTO switch on the mower, and you don’t hear it engage or hear the blades start turning, there is probably a problem with either the engagement mechanism or the clutch. The electric solenoid can go bad, the clutch can be worn out and slipping, or the clutch can be fused together by excessive heat. There may also be a safety system malfunction, which may not let the blades engage.
With the first problem, nothing will happen when you activate the switch. This is a telltale sign of an electrical problem. If the clutch is damaged, you may hear it slipping while it tries to engage, or you might hear your PTO engage and then stop right away, as it is designed for the fuse to fail first if it cannot turn the clutch.
Most Common Riding Lawn Mower Clutch Problems:
The Electric PTO is Not Getting the Voltage Needed, or the PTO Solenoid is Toast
If the solenoid switch that controls the electromagnetic clutch engagement is bad, you will not hear anything happen when you activate the switch. There are three common reasons for this: There could be a bad fuse, which is the easiest fix. The solenoid may not be getting enough voltage from the battery to engage, in which case you will want to test the voltage coming from the battery. The other possibility is that the solenoid is bad, and in this case, you will want to head down to your local small engine repair shop to obtain a new one.
The Clutch is Slipping, Damaged, or Fused Together
If you activate your PTO switch and you hear a squealing, screeching sound, disengage the PTO and turn off the mower. You may have something in the blades that is keeping them from turning, your PTO belt may be worn out, or worst-case scenario, you may have a lawn mower clutch problem. Whatever you do, NEVER GO NEAR THE BLADES WHILE THEY ARE SPINNING, OR THE PTO IS ENGAGED. It’s best to completely turn off the mower and remove the key before trying to service any part of the PTO system.
A Safety Switch Somewhere Else is Causing the Blades Not to Engage
There is the possibility that another safety mechanism or switch is keeping the PTO from engaging. There are multiple switches in most mowers to ensure that you are safely seated on the mower when the blades start spinning. This may be a safety switch in the seat, or possibly a switch in the emergency brake or transmission. Try shifting your mower into neutral, engaging and disengaging the emergency brake, and make sure your weight is centered on the seat while engaging the PTO switch. Sometimes the switch under the seat may go bad or get dirty, and it will not sense your weight on the seat. Your lawn mower blades won’t engage if this is the case.
Symptoms of a Bad PTO Clutch on Your Lawn Mower (Mechanical):
These symptoms may indicate a mechanical problem with the actual clutch of the mower.
The Clutch Makes Noise When Engaged
If this is happening, your clutch may have a bad bearing, the surface of the flywheel may not be in good condition, or your PTO belt or pulley may need replacement. The belt slipping may cause the noise, so the first thing to check would be that the belt is tight and not damaged.
The Clutch Causes the Engine to Rev Higher
If the engine is revving up higher when you engage the PTO, it becomes evident that the power transfer from the engine to the blades is not working as it should. This may indicate some of the same things mentioned above. Your actual clutch may have a bad bearing and not be spinning smoothly, causing the engine to use more power. The PTO pulley may also have a bad bearing which would cause the engine to supply more power to get it moving.
The PTO Clutch Starts, Then Immediately Stops, and Fuse is Blown
If the fuse to your PTO switch blows right away when you activate it, that could still indicate a mechanical problem. This could mean that the clutch was impossible for the motor to move, and the motor had to try and supply so much power that it blew the fuse. Your clutch may be seized up completely, there may be something stuck in the blades, or your PTO pulley may be seized up. Either way, you won’t be mowing until you figure out the problem.
Symptoms of a Bad PTO Clutch (Electrical):
The PTO Switch Makes No Sound When Activated
This can indicate that the actual switch is bad or is not receiving enough power from the battery. You will need to do some electric PTO clutch troubleshooting to fix this problem. Listed below are the possible problems to check for if you experience this. You will likely need a multimeter to check for these.
Check the Fuse – The fuse for the PTO System is the easiest part to check and change. It should not be burnt, and you should be able to see that there is still a solid connection.
Battery Voltage – The battery may not be supplying enough voltage to activate the solenoid. This is a common problem, as lawn mower batteries can lose charge while sitting.
PTO Solenoid – This is the actual electromagnetic switch that controls the clutch, and replacing this part is a little more in-depth. You can check for its function with a multimeter.
How to Test the PTO Clutch on Your Mower
For the purpose of testing the PTO clutch on your mower, you will need to use a multimeter. It doesn’t have to be anything fancy, it just needs the ability to check voltage, resistance, and amperage.
Testing the PTO Clutch (Mechanical)
First, perform a mechanical test on the clutch just to rule out any physical problems with the clutch. You will need to turn on your mower. Make sure the mower is in neutral or park, and that the emergency brake is engaged. Some mowers have differing safety features, and you may need to disengage the emergency brake to start the PTO.
With the mower running at full throttle, try engaging the PTO switch or lever. If you hear the blades try to start up, you can rule out the PTO solenoid. If the clutch is squealing or the mower engine starts revving higher, disengage the PTO and turn off the engine. You may have a bad bearing in the clutch, a bad contact surface on the flywheel, or a bad PTO pulley.
Also, check the belt for the PTO and make sure that it is not loose, frayed, cracked, or otherwise worn out. You can find replacement pulleys, belts, and clutch assembly parts at your local small engine repair shop. If you activate the PTO switch and your blades turn on without incident, Congratulations! You have a functional PTO clutch and you can mow away!
Testing the PTO Clutch (Electrical)
If you tried to activate the PTO in the last step and nothing happened, it’s time to check some electrical connections.
1) Fuse – First, look for the wire that goes to the PTO mechanism. There should be a small fuse box containing the fuse for the switch. If the fuse is blown, you will be able to see it. The metal connection inside the fuse will be melted, broken, or burnt-looking. This means that the clutch was trying to draw too much amperage for some reason, and it usually points to some sort of mechanical problem (bad bearing, etc.). Replacement fuses are cheap, and you can replace it with the same amperage fuse that was in there. Usually, they are 10 or 15A.
2) Battery – If the fuse is good, the next thing to check would be the battery. You want to make sure the battery is supplying the correct voltage to the parts of the mower. Take your multimeter, switch it to Volts, and place the positive (red) probe on the positive terminal of the mower battery. Take the negative (black) probe and place it on a metal part of the engine. If your battery is putting out the correct voltage, the meter should read about 12.6 volts. Anything under that and your battery will need a charge. If this checks out, all that is left to check is the function of the solenoid.
3) Solenoid Function – You will want to find the clutch assembly under the mower, with the mower turned off, and unplug the wire that comes from the PTO switch. Put the key in the mower and turn it only to the first click. You don’t want to start the mower up, you just want the battery turned on. You will need to switch your multimeter to Amperage and connect the black probe to a grounded metal piece. Next, you will need to insert the red probe into the wiring harness coming from the switch. Activate the PTO switch and this should give you a reading of about 4 amps. If there is no reading, it is likely that the switch is bad. You may need to contact the manufacturer to get the part number for that PTO switch.
If you checked for these lawnmower PTO clutch problems and everything worked, your clutch is in working condition and you are ready to mow!
Hi mate, I’m Farud. I have a Mcculloch m175h38rb ride on mower. How can I tell if the clutch is bad and if it is, can I still mow?
Hi Farud,
First, driving with a bad or “failed” clutch on a mower isn’t particularly dangerous or likely to damage more than the clutch itself, but it’s unlikely that you will be able to mow for very long. Any breaking mechanisms may also be worn down more while driving with a bad clutch than they would be otherwise.
Further, if your clutch is failing, it may “stick” in the on position and make it difficult to disengage the blades. If this happens, turn off the mower and remove the key. The clutch will need to be repaired or replaced before using the mower again.
To know if you have a failed clutch, look for the following signs:
– Is your clutch hard to use? If the clutch fails to engage or disengage without more than a reasonable amount of effort, your clutch could be failing.
– Does your engine rev every time you engage the clutch? If so, your clutch could be faulty.
If either of these criteria is true, you likely have a clutch with a mechanical problem that needs to be repaired or replaced. If neither of these is true, there may be a problem elsewhere that is interfering with how the clutch operates. This usually means a problem with the wiring to the clutch, your mower’s battery, the solenoid related to your clutch if your mower has one, or a fuse attached to the clutch.
I hope that helps 🙂
My husband purchased an old Craftsman DYT 4000 from a guy he works with last summer. We replaced the carb and it ran good and cut great last summer. We used it for the first time this spring last week. Now the blades are turning but not really fast like normal. It isn’t cutting the grass, just pushing it over. It doesn’t sound like the electric PTO is engaging correctly, but the blades are turning. Switch or electric clutch?
Hi Brenda 🙂
It sounds to me like that would be an issue with your clutch. If the blades engage at all, the switch should be working fine. Since your blades aren’t spinning as fast as they should I would guess that the clutch isn’t functioning properly, or that the f belt is worn out.
Aside from that, I would also recommend taking a look at the blade itself. Make sure that it is tightened securely, and that all grass and grime buildup has been cleaned from the blade and deck.
The only other thing that would cause the blades not to spin properly would be lack of power from the engine. However, if you’ve got a suspicion that the clutch is faulty I would check that out first.
Let me know how you get on!
I need to know how to put the clutch belt on
Hi Ted,
The process of belt replacement will vary depending on the type of mower you have, but generally speaking there are a few things you can expect to do. First, you will have to loosen or remove your variable speed pulley. In order to get some slack in the belt you can almost always expect to pull out a pulley or two. This is usually done by pulling out a handful of mounting screws around its edges, or by taking out its center bolt and fully disassembling it.
Now, with tension released, you can remove the old belt and then thread the new one in. Just be sure to route it the same way it came out. There will be some other parts that you’ll likely need to remove when doing this to free up space, but it really depends on the type of riding mower you have.
As long as you keep track of all the parts involved, you should be able to get your new belt on just by noticing how the old one is installed.
Good luck!
Tom.
I have a Cub Cadet 1515 which is having issues with the pto clutch. Last fall the blades quit spinning while cutting grass. I pulled the pto switch out and pushed in several times and the clutch would still not engage. So today I found the air gap on the clutch to be .035 inches which I thought might be the problem (too large). I removed the deck and started the engine and pulled out pto switch and clutch did not engage (pulley was not spinning). A few hours later I started the engine again and the pulley started spinning immediately without pulling out the PTO knob. So, I pulled out and pushed in the PTO switch several times and the pulley kept spinning. I checked the continuity on the PTO switch pushed in: Com a=.89, com b=1, com c=1 and pto switch pulled out: Com a=1, com b=0, com c=0. I think the PTO switch is OK. With the engine running the battery was putting out 13.40 volts and the voltage to the clutch was 14.05 volts. The resistance to the clutch was 5.9 ohms and the continuity was 0. Any ideas on what the problem may be?
Hi Doug 🙂
While I’m not a trained small engine mechanic, I can definitely offer my perspective.
You’re right that your clutch’s gap is off. From what I understand, the average gap is meant to be about half that wide (.016 inches). I’m having a hard time finding the specification from Cub Cadet, but I’ve been reading that other 1515 owners use a gap of 0.012”.
Your test results do seem to indicate that the PTO switch still works, and if the pulley can spin, I would assume engagement is the problem here. Try and adjust/shim your gap first. It seems like that should be your issue since you’ve had good readings from the electrical system.
If that doesn’t help the problem, make sure you’ve checked your brake switch and safety shut-down circuit too. If these are out of whack it could prevent your PTO switch from doing its job. If all else fails, you might want to consider going for a new PTO and belts. Hope this helps!
Tom.
Hi.. we have a Husquvarna zero turn CZ4817. Every time we try to engage the blades it rips through my wires on my clutch. I can’t find any information on this and how to fix? Some talk of a anti-rotation bracket but again I can’t find any information on that either?
Please help.
Hi Donita,
There is a part you need called a clutch tie-down. If you search on the internet for the following – Husqvarna CZ4817 CLUTCH TIE DOWN – you’ll find what you need. It’s a small $15-$25 bracket that bolts to the underside of where the engine sits. It slots between a cut-out on the clutch and stops it from spinning. If someone changed the clutch for you, they could have forgotten to put it back on. If the wires were just ripped out, then it probably fell off.
If you search on the internet, you’ll find some images that will show you exactly where it goes.
I hope you find the part you’re looking for.
Thanks, Tom.
I have a 1996 Toro Pro-line model # 30182-690727. While mowing the blades disengaged. Everything was within specification, so I suspected the delay module. I bypassed it and kept the relay for power transfer. I connected the wiring to a 12-volt battery to prove the wiring and everything worked. The system works directly from the alternator which puts out 28 volts ac. The regulator puts out varying voltage between 7.2 and 13 volts dc. When back probing the hot wire going to the clutch, I got 7amps and the clutch engaged. When I remove the meter it disengaged. I cleaned all my grounds and bought a new regulator for the hell of it. It still does not work. Any ideas? I’m stumped.
Hi Matthew,
Well, it seems you know your way around electrical systems better than I do. But I did come across a case where the inside of a clutch was shorted out but would still engage. The problem is that it was burning out switches. Now, I’m not sure if this would have anything to do with your case, but it could be something similar. Checking the resistance through the clutch with a multimeter might shed some light on the matter.
Also, I’ve heard of starter solenoids causing strange issues with clutches engaging and erratically disengaging.
I hope you get things sorted out.
Cheers, Tom.
The PTO clutch will stop the engine. The Engine stops when the PTO clutch is in “ON” position. Electrical switch under clutch? What should I look at?
I have a Stiga Villa mower.
Hi Aleks,
First, you want to make sure that the clutch can spin when the mower is switched off. If it’s seized, then it could trigger the engine to shut down.
Then, take a look at the safety switches to make sure that they are connected and working. Your mower could have a safety switch that requires you to have your foot on the brake to engage the PTO. If this is malfunctioning, then it will kill the engine.
Next, I would want to check the clutch itself. It could have shorted out and caused the engine to cut out when you tried to engage the PTO. You can test for the resistance through the clutch using a multimeter. At the same time, you can check the switch with the meter. By the sound of it, the switch seems to be working.
I hope this gives you some idea of where to look. Good luck!
Cheers, Tom.
MY SIMPLICITY CORONET 1694288 had a bad solenoid and I replaced and now starts fine. But when I release the clutch, it shuts down. What did I do wrong?
Hi George,
Well, I wouldn’t say you did anything wrong. It could just be a coincidence that when the starter solenoid went bad, so did something else. Or something else caused the clutch to go bad. Here are a few items that could be worth looking into.
Check the Safety Switches
First, run through the mower’s safety features. I’m sure you know that micro switches around the mower will cut the engine if safety isn’t followed as per the manufacturer’s design, such as sitting in the seat when you engage the PTO switch. Next, check that the switches are working correctly and are still connected to the wiring harness. These could have been disconnected when the solenoid was being replaced.
Check the Wiring Harness for Damage
Next, check the wiring harness for any damage. There could be a damaged cable causing a short and resulting in the mower cutting out once you engage the clutch. Once you’re confident that these are working correctly, move on to the clutch.
Checking the Clutch
First, set the ignition to ON (not start) with the mower’s engine off and engage the clutch. So you should hear the clutch click on and off as you move the switch. If it engages, then the switch should be ok. Next, you want to check the clutch. I’m not sure if you are handy with a multimeter, but if you are, you could test the resistance through the clutch. If the clutch is shorted out internally, it could be drawing too many amps from the battery. You can test the switch to see how many amps run through the circuit or how many ohms pass through the clutch. If the clutch is burned out, it could be drawing too much power and killing the engine. A clutch can still operate even if it is burned out electrically.
I hope this information can point you in the right direction.
Tom.
I have a Craftsman zero turn mower about 10 years old. Model 247.25001 42″ deck. The last year or two I’ve been having an intermittent problem with my PTO switch. I start the mower, turn on the switch and the blades engage fine. After about 30 minutes or so, sometimes longer (takes me about an hour or so to mow the lawn) I may stop the mower and blades to get off and clear the deck off, or move something (its setup for mulching). I’ll get back on the mower, engage the switch and nothing happens. However, if I leave the switch in the on position in about 3 – 5 minutes the blades will start up again. I changed the switch and it was a little better, but still doing the same thing. I had read something about overheating of the PTO switch and I see where they now sell 10 amp switches versus the 5 amp that came with the machine. Any ideas what this could be?.
Hi Robert,
It sounds like there could be an issue with the actual PTO clutch. Inside the clutch, there is an electromagnet that has windings. As these windings degrade, they can cause a short, which in turn changes the resistance through the PTO. What can happen is the PTO switch can overheat and damage the switch.
Basically, the change in resistance can cause an increased pull of amps and melt the switch. So, the fact that you changed the switch from a 5 amp to a 10 amp probably masked the issue for a while. I recommend disconnecting the electrical connector from the PTO and testing it with a multimeter. If you set your multimeter to ohms and connect the two probes to the clutch, you will be able to check the resistance.
Typically a PTO clutch will have a resistance between 2-4ohm. If your clutch is outside of this range, then this is likely the cause of the problem. You should be able to find the specific resistance for your PTO in your manual.
I hope this gives you an idea of what to check.
Thanks for the question.
Tom.
Hi Tom,
I have a Scag walk behind. There is a high pitched noise when I disengage the blades. Also I noticed when I spin the blades the clutch moves back and forth. Any thoughts? Are these issues related?
Thanks!
Hi Travis,
The clutch should be locked in place with a small metal bar/bracket. So the clutch should only move a tiny amount between the bracket. Now inside the clutch, there are a few bearings that allow the clutch to spin. I’m thinking that the bearings could be worn and are causing the noise, or the clutch isn’t properly installed, and it could have come loose. I would take a closer listen to see where the noise is actually coming from. It could be coming from the clutch, or it could be belt noise as the belt slips when the blades are disengaged.
First, I recommend that you inspect the clutch to make sure the bearings are ok and that the clutch is correctly installed. Then I would take a look at the belt and pulley system. If you are only having a problem when the blades engage/disengage, then it must have something to do with the driveshaft, clutch, belt, pulleys/spindles, or the deck.
I hope this gives you a few ideas.
Tom.