HELP! PTO quit mid-job!

[smartguyz]

Hi guys, I avoid using "HELP" in all caps unless it warrants it.

Today my trusty PT425 was happily mowing the yard when the PTO quit. I need advice on what to do to diagnose, fix, etc. (Note: Power-Trac Service Department is out for the week for Independence Day).

1. Was using the 48" fine-cut mower, flat ground, grass with some weeds, nothing unusual. PT was operating normally.
2. I turned off the PTO (to get off the tractor and move some lawn furniture out of the way).
3. I got back on the tractor and flipped the PTO switch. Nothing happened. Mower did NOT start spinning.
4. Flipped the switch on and off. Nothing.
5. I turned off the tractor and checked the belt and the blades for free movement. Everything turns freely, belt is fine.
6. Started tractor again. Flipped PTO switch. No movement.
7. Swapped over to the field mower to see if it was an implement failure. Field mower also does not turn. Therefore I think it is likely the PT pump itself.
8. Note: I do have a spare hydro filter, and I am due for the filter change.

What should I investigate next?

Thanks so much,

Rob

 

[johara1]

I would check the switch first.....See if you have power to the switch, then trace the wire down to to PTO. and see if you have power there... jim

 

[marrt]

I assume the engine does not bog down when flipping the PTO switch. I also assume you know where the PTO valve is located in the engine compartment.

1. Check battery. A low battery will cause this behavior even though the tractor will still start and run fine. Power Trac batteries have a short life in the hot engine compartment. This is most likely the problem.

2. If battery is good, check to see if PTO solenoid is getting power when PTO switch is flipped.

3. If above is OK, removed the large nut on the PTO solenoid and check for any rust or contamination on the PTO solenoid assembly (lift the large round outer assembly off after removing the nut). Clean, lightly lubricate with penetrating oil and replace. DO NOT overtighten large nut. It calls for 10 ft. lbs...which is finger tight plus a little more with a wrench.

4. If it still doesn't work, you can tap it lightly with the PTO switch flipped on.

5. If all that doesn't work, put the battery on a charger and let the tractor cool off completely and try it again.

Report back.

 

[smartguyz]

Thank you marrt. Battery is definitely low. I had to jump-start to get it started. I will replace the battery and report back.

WHY does the battery level affect the PTO circuit? Doesn't the fact that the alternator is charging the electrical system overcome a low battery?

-Rob

 

[marrt]

Thank you marrt. Battery is definitely low. I had to jump-start to get it started. I will replace the battery and report back.

WHY does the battery level affect the PTO circuit? Doesn't the fact that the alternator is charging the electrical system overcome a low battery?

-Rob

The short answer is no. On small engines, the alternator is like a trickle charger. It produces enough to keep the engine running, for example, but that doesn't take much. The PTO solenoid is electromagnetically operated and the inrush current requirement is significant. If the battery is weak, it doesn't have enough surplus current to actuate the solenoid...even though the alternator can supply enough to keep the tractor running.

As a side note for others, it's not good practice to rely on an alternator to recharge a battery (even on a full size vehicle). On a small engine in particular, a weak battery can require (pull) enough amperage to overload the relatively small alternator and burn it up. Therefore, if you have to "jump" the tractor to get it started, it's always best to stop and hook the battery to a charger before continuing. If this occurs frequently, it's a sign the battery may be at the end of its service life. I mentioned before that batteries have a tough time in a Power Trac machine due to the very high temps in the engine compartment. That doesn't mean they won't last long. It means it's important to keep and eye on them as they may fail sooner than expected.

 

[agjones]

+1 on the voltage. Great info above.

I've definitely been through a few switches for the pto. And once, the wire running between the two halves of the machine shorted... But I've stuffed more in that sleeve (extra hydraulic circuit) than the factory so that's not likely your issue.

 

[smartguyz]

GIANT SHOUT OUT to marrt!

marrt, your diagnosis was spot-on accurate. After replacing the battery, everything is back to normal! I owe you one!

THANK YOU!

-Rob

 

[agjones]

Great forum, great people.