What To Do If Your PTO Won’t Engage (Answered)

Written by Mathew Booe in Grass

Modern lawnmowers and garden tractors are chockful of technological features that make them safer and more efficient than ever. Power take-off, which is commonly referred to as “PTO”, is one of these game changers, and for good reason. But what if your PTO won’t engage?

For a PTO that won’t engage on your mower or tractor, testing and or replacing one of the three parts of the system could fix the issue. Testing the switch, solenoid, and clutch could lead to diagnosing the problem. Replacement is the most common fix for each issue.

In today’s article, we take a look at some of the problems that can affect your mower’s PTO system, with a particular focus on the switch mechanism. What causes a PTO to fail and, more importantly, what can you do to remedy (or prevent) such issues?

Contents

What Is A PTO On Lawn Tractors?

Firstly, we need to look at the basics of what a PTO system is and how it works. There are several moving parts and they work to make using mowers infinitely more safe than they were a generation ago.

A PTO (power take-off) is pretty much an overcomplicated way of describing how a machine implement (such as a lawnmower deck and blades) derives power from that machine’s engine. In the case of a lawnmower, PTO is what enables you to engage or disengage the mower blades while the engine is running.

Before this technology came on the scene, blades on rotary mowers would keep spinning for as long as the engine was running…something which is as dangerous as it sounds.

A quick glance at current lawnmower accident statistics (at a time when PTO is now the norm) hints that the pre-PTO era must have witnessed more than its fair share of landscaping carnage.

According to the National Institutes of Health (NIH) and the U.S. Consumer Product Safety Commission’s National Electronic Injury Surveillance System (NEISS) there were 934,394 lawn mower related injuries between 2005 and 2015. This equates to an average of 84,944 each year.

In a study done by researchers from the University of Chicago and the University of Virginia, the numbers were not significantly decreasing over this period. Yet, without a PTO system installed, these injuries would be much higher and admittance to hospitals would far exceed the 8.5% of incidents currently.

How Do PTO Systems Work On Lawn Mowers?

A PTO system is comprised of a PTO implement, a clutch, and a switch. All three of these parts work together to control the functionality of the blade spin.

A PTO system on a lawn mower works to control the ability of the blade under the mowing deck to spin. It is essentially a switch that turns on a magnetic pull from the solenoid via the clutch. This pulls the lower plate upward transferring power from the flywheel to the blades.

The clutch itself is comprised of upper and lower plates. The upper plate houses an electromagnet known as a solenoid. The lower plate is attached to the mower deck pulley and, ultimately, the blades themselves. Between the two plates is a flywheel that is attached to a shaft that is driven by the engine’s drive system.  

When the machine operator engages the switch, signals are sent to the clutch via electrical cables. This activates the solenoid’s magnetic pull, which attracts the lower plate towards the upper plate. However, the lower plate can’t reach the upper plate but is attached to the flywheel instead, making it (and the blades) rotate.

When the switch is disengaged, the signals are cut-off. This switches off the solenoid’s pull, which causes the lower plate to detach from the flywheel and stop rotating. Naturally, the blades will also stop spinning.

Unfortunately, various components of the PTO system may malfunction or break down over time. As one of the moving pieces in this equation, the switch is especially prone to this.

How Do I Know If My PTO Switch Is Bad?

If you suspect a wonky PTO switch, the only way to be certain is to remove it and test it. There are tools that can help you get an accurate reading on your switches operation.

To find out if your PTO switch is bad, you will need a multimeter that is set to the Ohms setting. The aim is to assess resistance levels between the switch’s pins. PTO switches feature pins that are plugged into a socket that is hooked up to the electrical cables linking to the clutch.

There are usually eight pins arranged in three rows. One end of the rows is known as the “normally closed” (NC) side and the other end is the “normally open” (NO) side. These sides are often labeled.

In simple terms, NO means the circuit is open by default, allowing the current to pass as long as the switch is set to on. The circuit is cut off when the switch is set to off. 

NC, on the other hand, means that the circuit is cut off when the switch is engaged. Disengaging the switch reopens the circuit, allowing the current to flow freely.

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How Do You Test A PTO Switch?

Since testing a PTO switch is the main way to diagnose the problem, how exactly is this done? Most issues revolve around the switch and it should be the first thing tested.

Step 1: Check Resistance With Switch Off

The first step of a PTO switch test involves placing one of the multimeters leads on an NO pin. The other lead must be placed on the corresponding NC pin in that row. Note that the PTO switch must be in the “off” position. If there is continuity between the two pins, the multimeter will beep and display a resistance reading.

After this, repeat the process for all corresponding outer pins. Again, if you get beeps and readings, you’re good…so far.

I recommend this inexpensive and popular multimeter from Amazon to accurately check your PTO switch.

Step 2: Resistance Check With PTO Switch On

The next phase of the test requires you to set the switch to the “on” position.

Now, you will be testing your NC pins against their corresponding middle pins. The NO pins are irrelevant for this part. Again, you will be looking for beeps and readings on the multimeter display.

Ultimately, if you get readings all the way through, it means there is continuity between pins, which is what a functional switch should have.

Step 3: Diagnose A Faulty PTO Switch

If at any point, you do not get beeps or readings, you can repeat the test (using different multimeters if you can). If it’s still no dice, then that’s a sure sign of a faulty switch.

You might be able to fix a PTO switch but these components are so cheap that replacement is usually less of a hassle.

Then there is the solenoid that creates the magnetic pull to bring the power to the flywheel. There are times this can be faulty.

How Do You Test A PTO Solenoid?

The solenoid in a PTO system is essentially an electromagnet that pulls the lower plate hooked to the blades upward toward the flywheel providing kinetic energy from the engine. There are several things that can cause it to stop working.

Step 1: Check Solenoid With Multimeter

The first thing that needs to be determined is if this electronic portion of the PTO assembly is working properly. To do this a multimeter is again your tool. Yet, there is another simple trick to test your mower’s selenoid.

First and foremost, don’t test your solenoid while it is installed in your mower. Take it out to protect other parts from power surges.

This next part is a great tip for any who have or have not tried this before. You don’t need special equipment, only a battery charger that can be hooked up to the proper poles on the solenoid. Then you can check the functionality in a few simple steps.

Step 2: Check For Debris

Though these magnets are fairly strong and can be relied upon to work through some harsh conditions, as they age debris can have more and more of an adverse affect on their functionality. This can even come in the form of metal shavings or objects along with built up debris from normal usage.

Clearing out objects and buildup can restore much of the functionality of the solenoid. Though on a newer mower this is less likely, on mowers with many hours of use this could be an issue.

If you have already checked the switch, this should be the next step.

Step 3: Look For Bent Parts

The spacing for the proper operation of a solenoid is crucial. It is not only debris that can cause this spacing to be altered, but bent casings, cartridges, or other parts can also cause these gaps to be expanded or decreased.

The issue here is the ability of the average owner to be able to fix this issue themselves. Though it can be done, most manufacturers suggest replacing the solenoid assembly.

How Much Does A PTO Clutch Cost?

With the clutch handling much of the operation of a PTO system, it is put to use quite a bit. This can cause it to be one of the needed replacements over the years of use for many mowers.

The cost of a mower PTO clutch ranges from $100 to $300 for the assembly alone. Most residential PTO clutch assemblies cost from $100 to $170. This is not including the installation charges that could take the replacement from a couple hundred dollars to closer to $1000.

To reduce the cost of installation, those comfortable with repairing and replacing parts on their own equipment can save quite a bit. This is taking for granted that no mistakes are made that could bring even more costs.

To get an idea of costs and availability of PTO clutches, here are some options for popular mower models available on Amazon.

What Else Would Cause A PTO Not To Engage?

Apart from the aforementioned faulty switch problem, there are a few possible reasons why your machine’s PTO system may fail to engage when you need it to.

Electrical Connections

The first reason is a disruption in the electrical connection. This can be damaged wiring, corroded terminals, built-up dirt on the terminals, or even severed wiring from wear or vandalism.

No Voltage To The Clutch

Another common problem with electric PTO systems is a lack of voltage at the clutch end. A quick multimeter test (on the voltage setting) should reveal the problem if any. The clutch solenoid required 12 volts to work correctly, so that’s the value you should get when you hook the leads up to the PTO cable end that connects to it.

Electromagnet Issues

If the voltage is there, but you’re still not getting any engagement, you might want to test the electromagnet itself.

This test is a resistance test using a multimeter on the Ohms setting. Place a lead on both poles of the electromagnet and observe the device display. If the magnet is working correctly, it should display a resistance value in the 1.5-3.0 range. Any lower or higher, and you’ve got problems.

Hand Levers

For mechanical PTO systems, we highly recommend that you inspect the linkage between your hand lever and the clutch. Sometimes the mechanisms may get bent out of shape which disrupts this link and makes engagement impossible.

The Final Touches On When A PTO Won’t Engage…

Problems with a PTO system can be frustrating, but like anything when we know how to go about solving the problem the stress melts away. There are primarily three parts to the system to check apart from general power and debris issues.

The simple fix for any one of these parts is to replace it. Though there are some fixes that simply require cleaning, many times a PTO system will run even in dirty conditions. Replacement parts are usually the way to go.

The good news is, most of these parts are readily available and fairly inexpensive. If you are not experienced in small engine repair, it is best to find a qualified expert you trust. They can do the job in a fraction of the time and make sure it is done right.

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References

https://www.adamstauffer.com/electric-pto-wont-engage-on-my-riding-mower.htm

https://www.munciepower.com/cms/files/Products/Literature/Documents/Troubleshooting/TRG08-04.pdf

Mathew Booe

Mathew has worked in landscaping professionally for over 10 years. He is a grandpa and frequently interviews other experienced landscapers and lawn care experts who are also grandpas for these articles.

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