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How to Test a PTO Clutch

by Chris Stevenson

The power takeoff clutch, or PTO, on a small engine uses electricity to engage a clutch to the main engine crankshaft. PTO clutches transfer rotational torque and power, typically used on small tractors to activate mower blades or tillers. The battery sends voltage to a magnetic armature and rotor, which engages the clutch and plate, allowing full contact. Problems arise when the clutch jams solid, slips excessively or the voltage becomes lost. A tractor owner can initiate a few tests to see if his PTO clutch functions properly, engaging and disengaging at the proper time.

Lift the utility vehicle up with a floor jack. Place two jack stands under the front frame and two jack stands under the rear frame, so the wheels sit above the pavement. Provide enough clearance to look under the mower deck and see the clutch drive assembly. Refer to your owner's manual for the battery location. Some riding seats tilt up for battery access. Place the positive lead of a voltmeter on the red, positive post on the battery.

Place the negative voltmeter lead on a good engine source. Read the volts. If the battery output indicates 12.5 volts or below, charge the battery. The PTO clutch will not engage without sufficient voltage.

Look for the in-line fuse between the electrical wiring harness from the lever switch to the PTO clutch assembly under the deck. Unscrew the cap wires to the fuse and look at the fuse filament. If the fuse appears black or the filament has blown, replace the fuse with the same ampere rating as the original.

Start the engine and let it warm up. Activate the lever to engage the clutch. From a distance, look underneath the deck and check for mower blade operation. If you hear a squealing noise, shut the engine off and remove the ignition key. Disconnect the negative battery cable with a socket.

Slide under the mower deck and remove any broken branches, twigs or other obstacles that might have jammed between the pulley and drive belt. Check the belt for tension by engaging the lever and feeling the tension on the belt. Replace any frayed, cut or worn drive pulley belts. Make the sure the idler pulley moves freely back and forth on its swivel.

Reconnect the negative battery cable with a socket. Insert the ignition key. Start the engine. Activate the PTO engagement lever, then disengage it. Turn it on and off several times. If you do not hear a disengagement noise or see the power takeoff pulley stopping or slowing down at any time, it indicates the clutch and plates have galled together from excessive heat, or the slip ring has jammed. This will necessitate a clutch removal and internal inspection.

Pull off the main power wire that goes to the PTO clutch assembly. This is located on the clutch side. Turn the wire jack toward you, but pull yourself back away from the deck as far as possible. With the battery connected and engine turned off, place the negative alligator lead of a test light to a ground source. Place the probe of the test light inside the wire connector, attaching it to the red lead that leads to the PTO clutch.

Activate the PTO clutch lever and look for the bulb to illuminate from the test light. No illumination means the engagement switch has failed at the lever-switch position. If the battery voltage reads correctly and the in-line fuse checks out, the lever switch will be the problem.

Use wire strippers to cut a length of jumper wire that will reach from the positive post on the battery to the red power lead inside the PTO wire jack. Make sure you connect the battery cables. Connect one end of the jumper wire to the positive side of the battery and the other end to the positive, red wire inside the PTO wire jack.

Listen for the click of engagement. If you can hear nothing, the problem lies within the electrical circuit of the PTO clutch assembly, most likely at the rotor and armature location.

Warning

  • Be very careful when running the engine and engaging the clutch for testing purposes. The clutch will spin the mower blades, and you do not want your head or hair anywhere near the underside of the mower deck. Observe from a distance, or summon the help of an assistant to turn your key and clutch engagement lever on, while you watch clutch operation.

Items you will need

About the Author

Chris Stevenson has been writing since 1988. His automotive vocation has spanned more than 35 years and he authored the auto repair manual "Auto Repair Shams and Scams" in 1990. Stevenson holds a P.D.S Toyota certificate, ASE brake certification, Clean Air Act certification and a California smog license.

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